Skip to main content
EERE » BTO » Building America » Solution Center Home » Guides A-Z » Air Sealed, Insulated Basements

Air Sealed, Insulated Basements

Print
Scope
The basement walls are covered with a dimpled plastic water barrier then wrapped with 3 inches of XPS rigid foam with seams taped to keep out water.
The basement walls are covered with a dimpled plastic water barrier then wrapped with 3 inches of XPS rigid foam with seams taped to keep out water.
Scope

Insulate a basement to improve the overall thermal performance of the building and provide more dry, usable conditioned space for home occupants and HVAC equipment.

  • Address site drainage and plan for water/moisture management.
  • Assess risks posed by insects and other pests. (See the International Code Council’s (ICC's) guide, Pest Prevention by Design). 
  • Assess and address radon issues. (See the EPA’s guide Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes, Also see Building Science Corporation’s (BSC's) information sheet on Soil Gas Control.)  
  • Design and install safe combustion systems in the home. (See the pre-retrofit assessment guide on combustion appliances.)
    • Sealed combustion equipment is strongly recommended.
    • Include carbon monoxide detectors.
  • Determine code, program, and/or other goals and requirements for basement insulation.
  • Consider insulating the foundation walls using exterior rigid insulation, insulated concrete forms, or prefabricated insulated concrete panels. If these are impractical (due to pest issues or because it’s an existing building), consider interior insulation systems.
  • Install systems per code requirements and manufacturer specifications.
  • Verify systems (such as drainage systems, combustion appliances, etc.) are installed properly and operating safely.
  • Ensure the ground surface slopes away from the foundation. Ensure good vertical drainage along the foundation wall by backfilling with free-draining soil or installing geotextile drainage mat or dimpled plastic drain mat on the exterior of the foundation wall, and provide horizontal drainage with an exterior footing drain pipe. This is especially important in cold climates where there are concerns with frost heave.

See the Compliance Tab for links to related codes and standards and voluntary federal energy-efficiency program requirements.

Description
Description

Because basements are largely below grade and winter ground temperatures are often warmer than winter air temperatures, the potential for heat loss from a basement is smaller than from the above-grade portions of a home’s envelope. While insulation levels below grade need not be as high as those of above-grade walls, insulating basements is critical to achieve the energy and comfort goals of high-performance homes. Figure 1 shows a basement insulated with insulated concrete forms (ICF), one of several options available for highly insulated basement walls.

The basement slab is wrapped in a blanket of insulation including R-27 of closed-cell spray foam under the slab and R-22 ICF blocks wrapping the slab edges.
The basement slab is wrapped in a blanket of insulation including R-27 of closed-cell spray foam under the slab and R-22 ICF blocks wrapping the slab edges.
The basement slab is wrapped in a blanket of insulation including R-27 of closed-cell spray foam under the slab and R-22 ICF blocks wrapping the slab edges.
View Image Download
Figure 1. The basement slab is wrapped in a blanket of insulation including R-27 of closed-cell spray foam under the slab and R-22 ICF blocks wrapping the slab edges (Source: Courtesy Of Greenhill Contracting).

This guide describes good practices for insulating basements in new and existing homes. This is by no means an exhaustive list; rather, it is a short list of systems that can work well, can comply with current codes, and can be practically implemented by builders and contractors. For multifamily construction, consider also the Solution Center guide Air Sealing and Compartmentalization in Multifamily Buildings, 

Before insulating a basement, be sure to assess (and address if necessary) key health, safety and durability issues. These include:

Where to Insulate

Foundation Walls or First Floor?

One of the first questions to answer when determining a basement insulation strategy iswhether to include the basement in the building envelope? If the basement will be part of the conditioned living space of the home, the insulation will be installed on the basement walls (either on the interior or exterior side of the walls). If the basement will not be part of the conditioned space than the insulation will be installed as part of the floor assembly of the first floor (usually between the floor joists). 

 

Insulating at the Walls

In most cases insulating the basement walls and slab results in better overall thermal performance of the home rather than excluding the basement from the conditioned space of the home. Insulating the basement walls, rather than under the first floor, brings the basement within the thermal envelope or conditioned space of the home and connects the basement thermally to the rest of the house. This will keep the basement warmer during the winter. In the summer, a conditioned basement will usually be dryer than an unconditioned basement. A warmer, dryer basement can have much more value as a functional, usable space. It also provides better conditions for HVAC equipment.

In extremely cold climates, insulating the basement walls may be critical to keep basement temperatures above freezing. This is especially important if there is mechanical equipment or plumbing in the basement, e.g., a boiler, furnace, water heater, ducts, and/or piping, Connecting the basement to the conditioned space will reduce the cooling load during the summer months because the ground is generally cooler than the air within the home. It’s true that good basement wall insulation will limit this cooling effect, but even a home with a well-insulated basement will generally require less air conditioning energy than the same home with an unconditioned basement and insulation installed only beneath the first floor.

 

Insulating Under the First Floor

Insulating under the first floor, rather than along the walls will result in an uninsulated basement that is outside the home’s thermal envelope. While insulating only beneath the first floor may result in reduced performance compared to a fully- insulated basement, there are some scenarios where this strategy is chosen. Reasons could include:

  • Water management. If moisture management strategies do not keep the basement consistently dry (e.g., if the area is prone to seasonal flooding), insulating at the first floor may be the best option to avoid repeated damage to water-susceptible materials.
  • Combustion safety. It is strongly recommended that airtight buildings exclude natural-draft combustion appliances from the insulated enclosure. If natural-draft appliances are located in the basement and are not likely to be replaced with non-combustion or sealed-combustion direct-vent appliances in the near future, air-sealing and insulating at the first floor may be a safer option than air-sealing and insulating the basement walls and floor. For information on assessing combustion safety see these guides:

  • Cost. While insulating the basement walls generally results in better performance, this strategy is often more expensive, because more insulation will be needed to cover the walls and labor costs will be higher. Some choose to insulate at the floor for cost reasons, especially for retrofit projects.

     

Inside or Outside of Foundation Walls?

If the basement will be part of the conditioned area or living space of the home, the  basement walls can be insulated along either the inside surface or the outside surface of the exterior walls. Insulating on the outside of a foundation wall is usually only a practical option in new construction due to the excavation costs associated with an exterior installation. Most retrofit strategies involve installing insulation on the inside of the foundation walls unless major excavation is already necessary for foundation repair or site water management.

In most cases, insulating on the outside can result in better moisture management of the foundation assembly, but there are challenges with protecting the insulation at and above grade. These challenges lead many designers and builders of new homes to choose interior basement insulation. Examples of both strategies—as well as challenges and limitations of each—are discussed below.

 

Systems Described

While there are many viable basement insulation strategies, common systems include:

  • Exterior rigid insulation on concrete walls
  • Insulated Concrete Forms (ICFs)
  • Precast foundations
  • Interior insulation:
    • Foil-faced rigid foam left exposed
    • Rigid foam covered with drywall

    • Spray foam covered with drywall.

       

Exterior Rigid Insulation on Block or Poured Concrete Walls

Rigid insulation board is attached to the exterior of the concrete from the base of the above-grade wall down to the footer. The board should be installed over a paint-on water proofing membrane. A dimpled plastic drainage sheet product can be installed over the membrane to provide hydrostatic pressure relief. The rigid insulation board can be installed in one or more layers (Figure 2), each one or more inches thick depending on the insulation level required for the climate zone. Seams should be taped and if more than one layer is installed the seams should be staggered to reduce the risk of water intrusion. Extruded polystyrene (XPS) foam, rigid fiberglass, and mineral wool boards are the most common materials for insulating the exterior of foundation walls. None of these materials retains water, so long-term thermal properties should not be significantly affected by moisture.

Right - The basement walls are wrapped with 3 inches of XPS rigid foam that will be taped at the seams then covered with a dimpled plastic water barrier.
Right - The basement walls are wrapped with 3 inches of XPS rigid foam that will be taped at the seams then covered with a dimpled plastic water barrier.
Right - The basement walls are wrapped with 3 inches of XPS rigid foam that will be taped at the seams then covered with a dimpled plastic water barrier.
View Image Download
Figure 2. The basement walls are wrapped with 3 inches of XPS rigid foam that will be taped at the seams then covered with a dimpled plastic water barrier (Source: Courtesy Of BrightLeaf Homes).

Rigid fiberglass and mineral wool boards have a thermal resistance of approximately R-4 per inch (ft2hr°F/Btu-in). To achieve the same R-value as XPS insulation, the thickness of these insulations must be approximately 25% greater than XPS (which is R-5 per inch).

In most cases, insulation on the exterior of basement walls can result in drier foundation assemblies and basement conditions. Because of the difficulty of accessing the foundation exterior in existing buildings, exterior foundation insulation is usually only practical for new construction. Other key challenges for exterior insulation systems are:

One common—though unacceptable—solution to protecting insulation at and above grade is simply to not insulate above-grade sections of the foundation wall (Figure 3). In this scenario, the un-insulated portion of the foundation wall (at grade and above) is exposed to the coldest temperatures. (Figure 4 shows an inside view of the wall shown in Figure 3; condensation and ice have formed on the inside surface of the wall.). Research has shown that insulating the top portion of the wall is by far the most critical for thermal performance; insulating only below-grade portions of the wall is ineffective in stopping heat transfer and leaves the thermal envelope incomplete.

Exterior fiberglass insulation on this new home was (incorrectly) cut to terminate below-grade after backfill, which will expose the above-grade portions of the foundation wall to cold temperatures
Exterior fiberglass insulation on this new home was (incorrectly) cut to terminate below-grade after backfill, which will expose the above-grade portions of the foundation wall to cold temperatures
Exterior fiberglass insulation on this new home was (incorrectly) cut to terminate below-grade after backfill, which will expose the above-grade portions of the foundation wall to cold temperatures
View Image Download
Figure 3. Exterior fiberglass insulation on this new home was (incorrectly) cut to terminate below-grade after backfill, which will expose the above-grade portions of the foundation wall to cold temperatures (Source: Measure Guideline: Basement Insulation Basics 2012). 
Because the above-grade potions of the wall lack exterior insulation, condensation and even ice form during cold winter conditions
Because the above-grade potions of the wall lack exterior insulation, condensation and even ice form during cold winter conditions
Because the above-grade potions of the wall lack exterior insulation, condensation and even ice form during cold winter conditions
View Image Download
Figure 4. Because the above-grade potions of the wall lack exterior insulation, condensation and even ice form during cold winter conditions (Source: Measure Guideline: Basement Insulation Basics 2012). 

Insulation must be extended to the top of the foundation wall to provide a seamless thermal barrier in conjunction with the above-grade walls (Figure 5). This above-ground insulation must be protected with a durable material that can withstand environmental wear including weather, sunlight, pests, and physical impacts (Figure 6). Protective materials can include stucco, fiber-cement boards, fiberglass panels, vinyl sheets, aluminum coil stock, or even pressure-treated plywood. (For more options see this article, How to Finish Exterior Foundation Insulation).

Exterior XPS basement insulation is correctly installed to completely cover the foundation wall
Exterior XPS basement insulation is correctly installed to completely cover the foundation wall
Exterior XPS basement insulation is correctly installed to completely cover the foundation wall
View Image Download
Figure 5. Exterior XPS basement insulation is correctly installed to completely cover the foundation wall (Source: Measure Guideline: Basement Insulation Basics 2012). 
Rolled fiberglass sheets are installed to protect exterior XPS at and above grade.
Figure 6. Rolled fiberglass sheets are installed to protect exterior XPS at and above grade (Source: Measure Guideline: Basement Insulation Basics 2012). 

Another potentially tricky detail is integrating the extra dimension of the foundation insulation into the above-grade walls. Two possible solutions are presented here. In Figure 7, above-grade walls also incorporate rigid exterior insulation. In this case, there is usually little difference between the two planes. However, if the above-grade walls do not have exterior insulation, there must be a curb, flashing, or transition that protects the insulation, manages drainage well, and is aesthetically acceptable. One possible solution is presented in Figure 6.

The exterior foundation walls and above-grade frame walls are both covered with exterior rigid insulation.
Figure 7. The exterior foundation walls and above-grade frame walls are both covered with exterior rigid insulation (Source: Courtesy of Steven Winter Associates). 
ICF bricks are stacked to form hollow walls that are reinforced with steel rebar before the concrete is poured in
ICF bricks are stacked to form hollow walls that are reinforced with steel rebar before the concrete is poured in
ICF bricks are stacked to form hollow walls that are reinforced with steel rebar before the concrete is poured in
View Image Download
Figure 8. ICF bricks are stacked to form hollow walls that are reinforced with steel rebar before the concrete is poured in (Source: Measure Guideline: Basement Insulation Basics 2012). 

When considering external foundation insulation strategies, it is critical to consider insects and pest management. While termites and other pests do not eat foam, they can easily tunnel through foam to reach wooden building components. Many insect management strategies incorporate a “vision strip,” typically a 3-inch gap in the insulation extending across the top of the foundation wall that exposes the concrete, so termite activity is visible. Another strategy is a termite “shield,” typically a piece of metal flashing that extends from the sill or insulation transition over the top of the foundation wall. These strategies do not necessarily stop termites, but the devices will force bugs out of the insulation where their presence can be noticed. See more information in the “Insect and Pest Management” section in the Success tab.

 

Insulated Concrete Forms (ICFs)

When making poured concrete foundation walls, builders typically use wood or metal forms to hold the concrete in place until it hardens. Another option is to use insulated concrete forms (ICFs) where the forms consist of hollow rigid foam blocks that stay in place after the concrete is poured to form a lasting layer of insulation on the inside and outside surface of the concrete wall. The rigid polystyrene foam (either EPS or XPS) is connected by polymer spacers to form large (e.g., 9”x18”) hollow blocks that are stacked in courses to form a hollow wall (Figure 8). The wall is reinforced with steel rebar that is run horizontally and vertically through the spacers then the hollow space is filled with concrete (Figure 8). Many ICF systems include vertical plastic or metal nailing strips to which interior and exterior finishings can be attached. See the guide Insulated Concrete Forms for more information.

ICFs can be used below and above grade to construct the entire wall.
Figure 9. ICFs can be used below and above grade to construct the entire wall (Source: Measure Guideline: Basement Insulation Basics 2012). 

Instead of “sandwiching” concrete between the foam layers, another system sandwiches the rigid foam insulation between two layers of concrete. This approach can solve concerns about thermal barriers, some moisture issues, and possibly pest management concerns.

 

PreCast Foundation Walls

Precast concrete foundations have a significant presence in several regional markets, in particular in the Northeast and Midwest. Both of these regions are dominated by full basement foundations in residential construction, and both regions have robust pre-cast concrete industries. Precast foundations are factory-produced concrete panels designed for a specific project, shipped to the job site, and set up with a crane. Some panels consist of a layer of rigid insulation sandwiched between two layers of concrete. Other products use a thinner concrete shell with molded concrete ribs every 16 or 24 inches. The panels are monolithically poured with top bond-beams, bottom footers, and the evenly spaced concrete ribs. These thin-shelled rib systems can come from the factory with a layer of rigid insulation adhered to the interior side of the shell and wrapped around the ribs. The ribs are usually faced with sheet metal which is placed over the rigid foam to serve as a nailing surface for the ribs, which act like walls studs. The cavities between the ribs can be filled with additional blown or batt insulation.
 
Pre-cast panels are typically set on a compacted crushed stone base with no additional footing needed (Figure 10). The crushed stone base is placed and compacted uniformly over the entire foundation area (including under the slab). The first panel is meticulously located to pre-surveyed points, and the remaining panels are positioned in reference to it. Joints between panels are typically treated with two large beads of poly-butyl caulk with come-along bolt connections used to draw the panels together, then the below-grade surface is treated with one of a variety of damp-proofing or moisture-proofing techniques.

Pre-cast foundations can be set in a single day. Panel bracing is critical prior to backfilling, so the floor deck will have to be installed with limited at-grade access. The time savings are also labor savings, but material costs for pre-cast foundations are generally higher. Total installed costs are similar to those of poured concrete foundations (especially near precast plants) and are dependent on local market conditions.

A precast insulated concrete panel foundation is set in place on a base of crushed rock.
Figure 10. A precast insulated concrete panel foundation is set in place on a base of crushed rock (Source: Measure Guideline: Basement Insulation Basics 2012). 

 

Insulation on Interior of Foundation Walls

Interior basement insulation is often the only practical option in existing homes. Even in new construction, challenges with protecting insulation at and above grade and with integrating the extra dimensions of exterior insulation may lead some builders to install interior insulation. Building America researchers have found that the best interior basement wall insulation strategies have several key features:

  • Non-fibrous insulation is installed directly in contact with the basement wall and there is no channel for air movement between the insulation and the concrete
  • The assembly is air sealed so that basement air (and the moisture in it) cannot move into the insulation assembly

  • No moisture-sensitive materials are in contact with the concrete walls or floor (this is often addressed by building codes).

     

Exposed, Foil-Faced, Polyisocyanurate Board

Polyisocyanurate has an R-value of approximately R-6 per inch (ft2hr°F/Btu-in), although typically one inch is installed to meet R-5 requirements, two inches are installed to reach R-10, and three inches are installed to reach R-15. The rigid polyiso boards may be fastened to the concrete with either construction adhesive or with mechanical fasteners. Figure 11 shows insulation attached using 1x strapping as a base for the fasteners. The polyiso boards should be completely sealed to each other and to the concrete wall (Figure 12). There should be no avenue for air movement between the foam and the foundation wall. Insulation seams can be sealed with caulk, foam, foil tape, or polypropylene tape. Caulk or foam should be used at the edges of the insulation (near the sill, the slab, around windows or doors, etc.).

The International Residential Code requires foam insulation to be covered with a thermal barrier for fire resistance (2015, 2021 IRC, Section R316.4). The most common type of barrier is drywall. Attaching drywall over foam can be costly; however, it is often already factored into project costs if the basement will be finished for living space.  At least one manufacturer of foil-faced polyisocyanurate board insulation has a product that is allowed to remain exposed if installed in a space not typically used as living space, per an International Code Council (ICC) Evaluation Services report (ICC 2006, NER-681). In many jurisdictions, this product can be left exposed against basement walls without drywall or an additional thermal barrier.

As with most systems described here, spray foam can be a good option to seal and insulate the sill and band joist areas. Many codes allow for this small area of foam to be left exposed in these locations (2015 IRC, Section R316.5.11).

Foil-faced polyiso foam is held in place along the interior of a basement wall with nails or screws through the furring strips. Seams are sealed with foil tape and all edges are sealed with caulk or foam.
Figure 11. Foil-faced polyiso foam is held in place along the interior of a basement wall with nails or screws through the furring strips. Seams are sealed with foil tape and all edges are sealed with caulk or foam (Source: Measure Guideline: Basement Insulation Basics 2012). 
Foil-faced polyiso insulation is sealed to the interior of the concrete foundation wall with caulk or adhesive.
Figure 12. Foil-faced polyiso insulation is sealed to the interior of the concrete foundation wall (Source: Courtesy of Steven Winter Associates). 

 

Polystyrene Board with Drywall

Both unfaced expanded polystyrene (EPS) and extruded polystyrene (XPS) rigid foam are common basement insulation materials, but they cannot be left exposed without a thermal barrier for fire protection (2015, 2021 IRC Section R316.4). The most common such barrier is ½-in. drywall.

Of these two foams (EPS and XPS), XPS is more commonly used because it has a higher R-value (R-5 per in. rather than R-4). One commonly cited drawback of XPS is that its blowing agent is a potent greenhouse gas, although product options with lower global warming potential are now available. As with the polyisocyanurate foam insulation systems, XPS foam can be attached to the wall with construction adhesive or with mechanical fasteners. Seams in the foam should be sealed, and the top and bottom edges should be sealed to the concrete with caulk or foam. In one method of mechanical attachment, fasteners are attached through 1x furring strips, which serve as a base for attaching drywall with screws. Using these furring strips against irregular walls can be more challenging, as concrete surfaces are not always smooth and the drywall may follow any irregularities in the furring or wall shape. While electrical wires can be run in the gap between the drywall and the foam, electrical boxes (when installed) must be recessed into the foam. The foam edges around these penetrations should also be air-sealed with caulk, foam, or tape.

Some builders choose to install a conventional framed wall to the inside of the rigid foam (Figure 13) to avoid wall irregularity. These framing cavities can be filled with batts or other appropriate cavity insulation. With the addition of a framed wall with cavity insulation, less rigid foam may be needed to meet target R-values. 

XPS is installed along basement walls before constructing a framed wall.
Figure 13. XPS is installed along concrete basement walls before constructing a framed wall (Source: Measure Guideline: Basement Insulation Basics 2012). 

 

Spray Foam with Framing and Drywall

Sprayed polyurethane foam can provide excellent air sealing and thermal resistance in many envelope systems. The chief drawback to the product is cost, as it is usually more expensive to install than rigid foam boards. Like unfaced foam boards, spray foam must be covered with a thermal barrier. While spray foam can be effective in many types of foundation walls, it is especially excellent for improving the thermal and moisture performance of irregular walls (such as stone foundations). As open-cell spray foam can absorb and retain water (up to 40% of its volume), closed-cell foam is recommended for most foundation wall applications.

A recommended spray-foam system for a poured-concrete or block wall is shown in Figure 14. Framing is installed at least one or two inches away from the interior surface of the foundation wall to allow space for a continuous layer of spray foam to be blown in behind the framing. Drywall is attached to the 2x4 framing and provides the thermal barrier. As with the XPS system discussed above, it’s possible to use a hybrid system with spray foam directly against the foundation wall and cavity insulation within the framing. It may also be practical to use 2x3 framing or steel framing in some applications.

Closed-cell spray foam insulates the inside surface of a foundation wall and provides a thermal break between the concrete and a 2x4 framed wall. The remaining cavity space can be filled with fiberglass or mineral wool insulation; the stud wall must be covered with drywall to provide the code-required thermal barrier.
Figure 14. Closed-cell spray foam insulates the inside surface of a foundation wall and provides a thermal break between the concrete and a 2x4 framed wall. The remaining cavity space can be filled with fiberglass or mineral wool insulation, and the stud wall must be covered with drywall to provide the code-required thermal barrier (Source: Courtesy of Steven Winter Associates). 

It bears repeating that proper moisture management is critical for basements. The figures in these sections show examples of moisture control strategies that may or may not be appropriate for a specific home. Proper water management should be assessed on a case-by-case basis. For a much more extensive description of water management, insulation, and air-sealing of basements, together with numerous detailed construction drawings, see the report Foundation Design Handbook by Oak Ridge National Laboratory and the University of Minnesota (2014).

 

Success
Ensuring Success

MOISTURE MANAGEMENT

Basements are essentially holes in the ground. As such, they are susceptible to filling with water. Water management is critical in providing for overall durability and healthy basement conditions. Water issues can be related to rain or storm water run-off, ground water intrusion, movement of moist air, water vapor movement, or bulk water leaks from inside the basement (e.g., plumbing leaks). Insulating basement walls without adequately addressing moisture management can simply mask problems down the road. In some cases, insulation can trap water in assemblies and cause more severe problems.

Moisture management MUST be addressed before insulating a basement. There is a great deal of information in the Solution Center on this topic.

 

INSECT AND PEST MANAGEMENT

Insect problems vary tremendously from region to region and even locally. Termites eat wood, and precautions should be taken for any wood assemblies located near grade. Termites do not eat most insulation products (such as foams and fiberglass), but they can tunnel through these materials to reach food sources in the building.

Termites are not generally visible when they tunnel through insulation. Some codes require a “vision strip,” which is a gap in the insulation that force pests to come out into the open. Vision strips do not stop insects, but they make them more noticeable. In areas with a high likelihood of termites, regular inspections should be conducted. If termites are present, their mud tunnels will likely be visible where they cross the vision strip in search of food. When other pests are identified, other control measures must be taken.

Vision strips have a significant drawback: they require gaps in the insulation. These gaps are generally near grade where insulation is most important thermally because of larger temperature differentials. Where possible, it is recommended to use termite shields rather than insulation gaps in insulation (Figure 1). A termite shield usually consists of a strip of metal flashing that is laid over the top of the foundation wall and below the sill plate. The metal extends out at least 3/4 (0.75) inch from the wall and/or the top of the rigid insulation installed on the interior or exterior surface of the foundation wall. It won’t necessarily stop termites from getting up into the wood framing but, because they can’t chew through the metal, they will have to come out of the insulation to go around it. The mud tunnels they leave on the metal shield will be a visible indicator that they are present. Once detected other pest treatment steps can be taken. 

 

A termite shield extends over the top of the foundation wall and the exterior rigid foundation insulation. The shield separates the insulation on the foundation wall from the exterior rigid insulation on the above-grade frame walls.
Figure 1. A termite shield extends over the top of the foundation wall and the exterior rigid foundation insulation. The shield separates the insulation on the foundation wall from the exterior rigid insulation on the above-grade frame walls Source: Steven Winter Associates).

 

There are also insulation products available including some XPS foam boards with pesticides incorporated into them. Manufacturers of these products often recommend termite shields or similar barriers be used as well.

Termites can represent a substantial durability risk in some areas. Where termites are present, termite shields or other measures should be included in the insulation strategy. If effective pest management cannot be incorporated effectively into the foundation insulation systems, other strategies should be considered, such as insulating beneath the first floor. For more guidance, see "Pests" under "Disaster Resistance" in the Solution Center.

 

Combustion safety

Basements are often home to combustion appliances such as boilers, furnaces, and water heaters. Atmospherically vented appliances (where exhaust gases are drawn up a flue by natural convection) require substantial amounts of air in the room in which the appliance is located (referred to as the combustion appliance zone or CAZ). When the appliance is located in an uninsulated basement, that air is often drawn through cracks and air leaks around windows and at rim joists. If the basement is later insulated and air sealed, those air sources will be sealed off, which can cause problems with proper combustion and can potentially lead to dangerous conditions like back drafting. Ensure that combustion appliances are operating appropriately and safely before and after sealing and insulating a basement. 

The best way to avoid combustion problems is to install non-combustion equipment or sealed-combustion equipment. Sealed-combustion, direct-vented appliances draw air directly from outside through their own dedicated air inlet pipes and they exhaust air directly outside through sealed flues so they do not draw air from the CAZ. If combustion equipment other than sealed-combustion equipment is present in a home, have a qualified contractor assess combustion safety before and after retrofitting, as described in the guides Combustion Appliance Zone Testing and Pre-Retrofit Assessment of Combustion Appliances.

 

radon

Radon is a radioactive gas that occurs naturally in some soils and rocks and can cause health problems at higher concentrations. For more information on radon testing and mitigation, see this Solution Center guide on radon mitigation and the EPA website Radon-Resistant New Construction Builder/Contractor Resources.

Climate
Climate

During warm seasons in humid climates, humid air can leak into an air-sealed basement through cracks, such as around windows and rim joists. This humid air can condense on cooler surfaces such as floor joists or below-grade wall surfaces, causing moisture issues in the basement. In cold climates an uninsulated basement can expose HVAC equipment and plumbing located therein to excessively cold temperatures. 

Minimum insulation levels for basements are specified by climate zone in the International Energy Conservation Code (IECC). The insulation levels for the past several IECC and IRC code versions (2009, 12, 15, 18, and 21) are summarized in the Solution Center in the 2009-2021 IECC and IRC Minimum Insulation Requirements for New Homes. See the Compliance tab for relevant code information.
To determine your climate zone see the maps below or go to the 2021 IECC Climate-Specific Building Assemblies tool in the Solution Center and click on the “Help me find by Climate Zone”: button. The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the 2009, 12, 15, and 18 IECC. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. 

Consult with local code authorities regarding foundation inspection requirements for termites and requirements for radon mitigation. Also see the Description and Success tabs for more information and resources on these topics.

IECC climate zone map
IECC climate zone map
IECC climate zone map
View Image Download
Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18. (Source: 2012 IECC)
Climate Zone Map from IECC 2021
Climate Zone Map from IECC 2021
Climate Zone Map from IECC 2021
View Image Download
Figure 2. Climate Zone Map from IECC 2021. (Source: 2021 IECC)

 

Cold Climates

In all climates, but especially in cold climates where there are concerns about frost heave, ensure the ground surface slopes away from the foundation. Also ensure good vertical drainage along foundation wall by backfilling with free-draining soil or installing geotextile drainage mat on the exterior of foundation walls, and good horizontal drainage with exterior footing drain pipe. 

 

Pests

Where termite infestation is heavy (Figure 3), install termite shields at the top of the foundation wall beneath the sill plate that extend out of the wall at least 3/4 (0.75) inch on either side of the sill plate. If rigid foam is installed on the basement wall, leave a termite inspection strip or gap in the insulation to allow inspection of the wall for the presence of termite tunnels, as described in the Success tab.

Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
View Image Download
Figure 3. Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7) (Source: Courtesy of PNNL).
Training
Right and Wrong Images
Right – A dimpled-plastic rain mat was attached to the exterior below-ground walls to help minimize frost damage in cold climates.
Right – A dimpled-plastic rain mat was attached to the exterior below-ground walls to help minimize frost damage in cold climates.
Right – A dimpled-plastic rain mat was attached to the exterior below-ground walls to help minimize frost damage in cold climates.
View Image Download
Right – A termite inspection gap is left at the top of the rigid foam board basement wall insulation.
Right – A termite inspection gap is left at the top of the rigid foam board basement wall insulation.
Right – A termite inspection gap is left at the top of the rigid foam board basement wall insulation.
View Image Download
Right – After installing the insulated concrete foundation wall panels, the builder installed underslab rigid foam, which was topped by 4 inches of crushed rock then the poured slab.
Right – After installing the insulated concrete foundation wall panels, the builder installed underslab rigid foam, which was topped by 4 inches of crushed rock then the poured slab.
Right – After installing the insulated concrete foundation wall panels, the builder installed underslab rigid foam, which was topped by 4 inches of crushed rock then the poured slab.
View Image Download
Right - Basement slab with a capillary break of either gravel or a drainage mat.
Right - Basement slab with a capillary break of either gravel or a drainage mat.
Right - Basement slab with a capillary break of either gravel or a drainage mat.
View Image Download
Right - Basement with exterior XPS or EPS insulation and insulation under the basement slab.
Right - Basement with exterior XPS or EPS insulation and insulation under the basement slab.
Right - Basement with exterior XPS or EPS insulation and insulation under the basement slab.
View Image Download
Right - Basement with interior semi-permeable XPS or EPS insulation.
Right - Basement with interior semi-permeable XPS or EPS insulation.
Right - Basement with interior semi-permeable XPS or EPS insulation.
View Image Download
Right - Closed-cell spray foam is used to retrofit an existing rubble basement foundation wall.
Right - Closed-cell spray foam is used to retrofit an existing rubble basement foundation wall.
Right - Closed-cell spray foam is used to retrofit an existing rubble basement foundation wall.
View Image Download
Right - Concrete masonry unit (CMU) basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
Right - Concrete masonry unit (CMU) basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
Right - Concrete masonry unit (CMU) basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
View Image Download
Right – Construction adhesive is applied to the rigid foam panels that will be installed on the interior basement walls.
Right – Construction adhesive is applied to the rigid foam panels that will be installed on the interior basement walls.
Right – Construction adhesive is applied to the rigid foam panels that will be installed on the interior basement walls.
View Image Download
Right - Potential locations for basement insulation in new construction, slab insulation should always be underneath, with walls insulated (a) inside, (b) outside, (c) sandwiched inside, or (d) inside and outside of walls.
Right - Potential locations for basement insulation in new construction, slab insulation should always be underneath, with walls insulated (a) inside, (b) outside, (c) sandwiched inside, or (d) inside and outside of walls.
Right - Potential locations for basement insulation in new construction, slab insulation should always be underneath, with walls insulated (a) inside, (b) outside, (c) sandwiched inside, or (d) inside and outside of walls.
View Image Download
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the inside of the rigid foam.
View Image Download
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the outside of the rigid foam.
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the outside of the rigid foam.
Right - Poured concrete basement wall showing exterior insulation and sill detail; above-grade wall has sheathing to the outside of the rigid foam.
View Image Download
Right – Precast concrete basement walls come to the site with integrated insulation and steel-faced concrete studs.
Right – Precast concrete basement walls come to the site with integrated insulation and steel-faced concrete studs.
Right – Precast concrete basement walls come to the site with integrated insulation and steel-faced concrete studs.
View Image Download
Right - Precast concrete basement walls come to the site with integrated rigid foam insulation and steel-faced concrete studs.
Right - Precast concrete basement walls come to the site with integrated rigid foam insulation and steel-faced concrete studs.
Right - Precast concrete basement walls come to the site with integrated rigid foam insulation and steel-faced concrete studs.
View Image Download
Right - Prevent condensation in fibrous insulation-filled basement wall cavities by installing rigid or spray foam between the frame wall and the concrete foundation wall and by not installing a Class I vapor retarder over the framed wall.
Right - Prevent condensation in fibrous insulation-filled basement wall cavities by installing rigid or spray foam between the frame wall and the concrete foundation wall and by not installing a Class I vapor retarder over the framed wall.
Right - Prevent condensation in fibrous insulation-filled basement wall cavities by installing rigid or spray foam between the frame wall and the concrete foundation wall and by not installing a Class I vapor retarder over the framed wall.
View Image Download
Right - Retrofit of an existing basement slab by adding dimple plastic mat, rigid foam insulation, and a floating subfloor.
Right - Retrofit of an existing basement slab by adding dimple plastic mat, rigid foam insulation, and a floating subfloor.
Right - Retrofit of an existing basement slab by adding dimple plastic mat, rigid foam insulation, and a floating subfloor.
View Image Download
Right - Rigid foam insulation is taped at seams and installed over a drainage pad of aggregate to serve as a capillary break under the basement slab.
Right - Rigid foam insulation is taped at seams and installed over a drainage pad of aggregate to serve as a capillary break under the basement slab.
Right - Rigid foam insulation is taped at seams and installed over a drainage pad of aggregate to serve as a capillary break under the basement slab.
View Image Download
Right - Rigid foam is installed over a waterproofing membrane that has been applied to the basement foundation walls.
Right - Rigid foam is installed over a waterproofing membrane that has been applied to the basement foundation walls.
Right - Rigid foam is installed over a waterproofing membrane that has been applied to the basement foundation walls.
View Image Download
Right - Section view showing how to air-seal and insulate a basement wall with perforated blanket insulation by installing it over air-sealed rigid insulation board to reduce condensation risk in the fiberglass blanket.
Right - Section view showing how to air-seal and insulate a basement wall with perforated blanket insulation by installing it over air-sealed rigid insulation board to reduce condensation risk in the fiberglass blanket.
Right - Section view showing how to air-seal and insulate a basement wall with perforated blanket insulation by installing it over air-sealed rigid insulation board to reduce condensation risk in the fiberglass blanket.
View Image Download
Right - The basement foundation is insulated on the exterior and termite shield extends out past the top of the insulation.
Right - The basement foundation is insulated on the exterior and termite shield extends out past the top of the insulation.
Right - The basement foundation is insulated on the exterior and termite shield extends out past the top of the insulation.
View Image Download
Right – The basement of this cold-climate home is insulated along interior walls with 2 inches of foil-faced rigid foam; finished basement walls also have a 2x4 interior wall insulated with R-19 blown-in fiberglass insulation and a poly vapor barrier.
Right – The basement of this cold-climate home is insulated along interior walls with 2 inches of foil-faced rigid foam; finished basement walls also have a 2x4 interior wall insulated with R-19 blown-in fiberglass insulation and a poly vapor barrier.
Right – The basement of this cold-climate home is insulated along interior walls with 2 inches of foil-faced rigid foam; finished basement walls also have a 2x4 interior wall insulated with R-19 blown-in fiberglass insulation and a poly vapor barrier.
View Image Download
Right - The concrete basement wall is insulated on the interior with rigid foam; the footing detail is shown.
Right - The concrete basement wall is insulated on the interior with rigid foam; the footing detail is shown.
Right - The concrete basement wall is insulated on the interior with rigid foam; the footing detail is shown.
View Image Download
Concrete masonry unit (CMU) basement wall with exterior insulation, footing detail
Right - The concrete masonry unit (CMU) basement wall has exterior insulation; the footing details include interior and exterior footing drain pipe.
Right - The concrete masonry unit (CMU) basement wall has exterior insulation; the footing details include interior and exterior footing drain pipe.
View Image Download
Right - The conditioned basement is insulated on the interior with 1 inch of polyiso R-6.3 rigid insulation.
Right - The conditioned basement is insulated on the interior with 1 inch of polyiso R-6.3 rigid insulation.
Right - The conditioned basement is insulated on the interior with 1 inch of polyiso R-6.3 rigid insulation.
View Image Download
Right - The existing basement slab is retrofitted by installing a dimple plastic drainage mat, rigid foam insulation, and a floating subfloor.
Right - The existing basement slab is retrofitted by installing a dimple plastic drainage mat, rigid foam insulation, and a floating subfloor.
Right - The existing basement slab is retrofitted by installing a dimple plastic drainage mat, rigid foam insulation, and a floating subfloor.
View Image Download
Right - The poured concrete basement walls are insulated along the inside with 2.5 inches of extruded polystyrene insulation.
Right - The poured concrete basement walls are insulated along the inside with 2.5 inches of extruded polystyrene insulation.
Right - The poured concrete basement walls are insulated along the inside with 2.5 inches of extruded polystyrene insulation.
View Image Download
Right – The rim joists above the pre-insulated basement walls are sealed and insulated with spray foam to prevent air leakage at this juncture in the building envelope.
Right – The rim joists above the pre-insulated basement walls are sealed and insulated with spray foam to prevent air leakage at this juncture in the building envelope.
Right – The rim joists above the pre-insulated basement walls are sealed and insulated with spray foam to prevent air leakage at this juncture in the building envelope.
View Image Download
Right - The slab-edge insulation is finished with stucco.
Right - The slab-edge insulation is finished with stucco.
Right - The slab-edge insulation is finished with stucco.
View Image Download
Right - This concrete basement wall has exterior rigid insulation and comprehensive moisture management details.
Right - This concrete basement wall has exterior rigid insulation and comprehensive moisture management details.
Right - This concrete basement wall has exterior rigid insulation and comprehensive moisture management details.
View Image Download
Right - This concrete basement wall is insulated on the interior basement walls with spray foam and under the slab with rigid foam; footing details are shown.
Right - This concrete basement wall is insulated on the interior basement walls with spray foam and under the slab with rigid foam; footing details are shown.
Right - This concrete basement wall is insulated on the interior basement walls with spray foam and under the slab with rigid foam; footing details are shown.
View Image Download
Right - This concrete basement wall is insulated on the interior with rigid insulation; sill details are shown.
Right - This concrete basement wall is insulated on the interior with rigid insulation; sill details are shown.
Right - This concrete basement wall is insulated on the interior with rigid insulation; sill details are shown.
View Image Download
Right - This concrete basement wall is insulated on the interior with spray foam insulation; sill detail are shown.
Right - This concrete basement wall is insulated on the interior with spray foam insulation; sill detail are shown.
Right - This concrete basement wall is insulated on the interior with spray foam insulation; sill detail are shown.
View Image Download
Right - This poured concrete basement wall is insulated on the exterior and under the slab with rigid insulation; footing details include interior and exterior footing drain pipe.
Right - This poured concrete basement wall is insulated on the exterior and under the slab with rigid insulation; footing details include interior and exterior footing drain pipe.
Right - This poured concrete basement wall is insulated on the exterior and under the slab with rigid insulation; footing details include interior and exterior footing drain pipe.
View Image Download
Right – Two inches of rigid foam was installed on the ground before pouring the basement floor slab while precast, pre-insulated concrete panels comprise the basement walls.
Right – Two inches of rigid foam was installed on the ground before pouring the basement floor slab while precast, pre-insulated concrete panels comprise the basement walls.
Right – Two inches of rigid foam was installed on the ground before pouring the basement floor slab while precast, pre-insulated concrete panels comprise the basement walls.
View Image Download
Right - Workers installed rigid foam on the floor and the sill plates of these pre-cast, pre-insulated concrete wall panels to provide a continuous layer of insulation under and around the not-yet-poured basement floor slab.
Right - Workers installed rigid foam on the floor and the sill plates of these pre-cast, pre-insulated concrete wall panels to provide a continuous layer of insulation under and around the not-yet-poured basement floor slab.
Right - Workers installed rigid foam on the floor and the sill plates of these pre-cast, pre-insulated concrete wall panels to provide a continuous layer of insulation under and around the not-yet-poured basement floor slab.
View Image Download
Right – Workers pour the concrete for the basement floor slab over a vapor barrier installed over rigid foam.
Right – Workers pour the concrete for the basement floor slab over a vapor barrier installed over rigid foam.
Right – Workers pour the concrete for the basement floor slab over a vapor barrier installed over rigid foam.
View Image Download
Right - A continuous layer of rigid foam insulation is installed against the foundation, and the perforated fiberglass insulation blanket is installed over that and covered with a semipermeable facing.
Right - A continuous layer of rigid foam insulation is installed against the foundation, and the perforated fiberglass insulation blanket is installed over that and covered with a semipermeable facing.
Right - A continuous layer of rigid foam insulation is installed against the foundation, and the perforated fiberglass insulation blanket is installed over that and covered with a semipermeable facing.
View Image Download
Right - Air barrier is present and installed between the floor system and unconditioned space.
Right - Air barrier is present and installed between the floor system and unconditioned space.
Right - Air barrier is present and installed between the floor system and unconditioned space.
View Image Download
Right - Below-grade concrete has been properly sealed against moisture and is now having insulation installed.
Right - Below-grade concrete has been properly sealed against moisture and is now having insulation installed.
Right - Below-grade concrete has been properly sealed against moisture and is now having insulation installed.
View Image Download
Right - Closed-cell spray foam was applied to the interior of a foundation wall.
Right - Closed-cell spray foam was applied to the interior of a foundation wall.
Right - Closed-cell spray foam was applied to the interior of a foundation wall.
View Image Download
Right - Closed-cell spray foam covers the interior of the foundation wall and wall framing is placed to the inside of the spray foam.
Right - Closed-cell spray foam covers the interior of the foundation wall and wall framing is placed to the inside of the spray foam.
Right - Closed-cell spray foam covers the interior of the foundation wall and wall framing is placed to the inside of the spray foam.
View Image Download
Right - Reduce condensation risks to blanket insulation by installing perforated vapor retarder covered fiberglass blankets over rigid foam that is air-sealed at all edges; staple the blanket to nailers and top/bottom plates and tape over the seams.
Right - Reduce condensation risks to blanket insulation by installing perforated vapor retarder covered fiberglass blankets over rigid foam that is air-sealed at all edges; staple the blanket to nailers and top/bottom plates and tape over the seams.
Right - Reduce condensation risks to blanket insulation by installing perforated vapor retarder covered fiberglass blankets over rigid foam that is air-sealed at all edges; staple the blanket to nailers and top/bottom plates and tape over the seams.
View Image Download
Right - Rigid foam insulation is installed along the exterior edge of an existing foundation slab.
Right - Rigid foam insulation is installed along the exterior edge of an existing foundation slab.
Right - Rigid foam insulation is installed along the exterior edge of an existing foundation slab.
View Image Download
Right - Rigid foam slab edge insulation is installed along the exterior edge of a monolithic slab foundation.
Right - Rigid foam slab edge insulation is installed along the exterior edge of a monolithic slab foundation.
Right - Rigid foam slab edge insulation is installed along the exterior edge of a monolithic slab foundation.
View Image Download
Right - Foil-faced polyisocyanurate rigid foam board is tightly installed and sealed against a concrete foundation wall prior to installing fibrous blanket insulation.
Right - Foil-faced polyisocyanurate rigid foam board is tightly installed and sealed against a concrete foundation wall prior to installing fibrous blanket insulation.
Right - Foil-faced polyisocyanurate rigid foam board is tightly installed and sealed against a concrete foundation wall prior to installing fibrous blanket insulation.
View Image Download
Right - Sub-floor insulation is properly installed and supported.
Right - Sub-floor insulation is properly installed and supported.
Right - Sub-floor insulation is properly installed and supported.
View Image Download
Right - The blanket fiberglass insulation is installed over a continuous layer of rigid foam insulation; the fiberglass is covered with a vapor retarder that is tape sealed at the seams.
Right - The blanket fiberglass insulation is installed over a continuous layer of rigid foam insulation; the fiberglass is covered with a vapor retarder that is tape sealed at the seams.
Right - The blanket fiberglass insulation is installed over a continuous layer of rigid foam insulation; the fiberglass is covered with a vapor retarder that is tape sealed at the seams.
View Image Download
Right - The precast insulated concrete walls of the basement provide a conditioned space for the high-efficiency (18 SEER, 9.5 HSPF) air-source heat pump, with its variable-speed fan, five-stage compressor, and MERV 11 filter.
Right - The precast insulated concrete walls of the basement provide a conditioned space for the high-efficiency (18 SEER, 9.5 HSPF) air-source heat pump, with its variable-speed fan, five-stage compressor, and MERV 11 filter.
Right - The precast insulated concrete walls of the basement provide a conditioned space for the high-efficiency (18 SEER, 9.5 HSPF) air-source heat pump, with its variable-speed fan, five-stage compressor, and MERV 11 filter.
View Image Download
Right – The seam between the slab and the foundation wall is sealed with urethane caulk.
Right – The seam between the slab and the foundation wall is sealed with urethane caulk.
Right – The seam between the slab and the foundation wall is sealed with urethane caulk.
View Image Download
Right - XPS rigid foam board is tightly installed against a concrete foundation wall and seams are sealed with tape prior to installing fibrous blanket insulation.
Right - XPS rigid foam board is tightly installed against a concrete foundation wall and seams are sealed with tape prior to installing fibrous blanket insulation.
Right - XPS rigid foam board is tightly installed against a concrete foundation wall and seams are sealed with tape prior to installing fibrous blanket insulation.
View Image Download
Wrong - Air leakage from the conditioned space to the basement foundation wall can lead to condensation or moisture issues in a conventional blanket insulation installation.
Wrong - Air leakage from the conditioned space to the basement foundation wall can lead to condensation or moisture issues in a conventional blanket insulation installation.
Wrong - Air leakage from the conditioned space to the basement foundation wall can lead to condensation or moisture issues in a conventional blanket insulation installation.
View Image Download
Wrong - Basement rim joist not sealed.
Wrong - Basement rim joist not sealed.
Wrong - Basement rim joist not sealed.
View Image Download
Wrong - Basement window not sealed.
Wrong - Basement window not sealed.
Wrong - Basement window not sealed.
View Image Download
Wrong - Class I vapor retarder over framed basement walls can cause condensation, mold, and rotting because plastic prevents drying to the inside; the outside should have waterproofing and vertical drainage, and the framing should be spaced from the wall.
Wrong - Class I vapor retarder over framed basement walls can cause condensation, mold, and rotting because plastic prevents drying to the inside; the outside should have waterproofing and vertical drainage, and the framing should be spaced from the wall.
Wrong - Class I vapor retarder over framed basement walls can cause condensation, mold, and rotting because plastic prevents drying to the inside; the outside should have waterproofing and vertical drainage, and the framing should be spaced from the wall.
View Image Download
Wrong - Crawlspace hatches should have weatherstripping and insulation when excluding the crawlspace from the building thermal envelope.
Wrong - Crawlspace hatches should have weatherstripping and insulation when excluding the crawlspace from the building thermal envelope.
Wrong - Crawlspace hatches should have weatherstripping and insulation when excluding the crawlspace from the building thermal envelope.
View Image Download
Wrong - Do not install a Class I vapor retarder over vapor-permeable insulation on the interior of a foundation wall because the vapor retarder can trap moisture in the wall, which can lead to mold.
Wrong - Do not install a Class I vapor retarder over vapor-permeable insulation on the interior of a foundation wall because the vapor retarder can trap moisture in the wall, which can lead to mold.
Wrong - Do not install a Class I vapor retarder over vapor-permeable insulation on the interior of a foundation wall because the vapor retarder can trap moisture in the wall, which can lead to mold.
View Image Download
Wrong - Moisture from within the basement foundation wall can migrate into the insulation cavity in a conventional blanket insulation installation.
Wrong - Moisture from within the basement foundation wall can migrate into the insulation cavity in a conventional blanket insulation installation.
Wrong - Moisture from within the basement foundation wall can migrate into the insulation cavity in a conventional blanket insulation installation.
View Image Download
Wrong - No air barrier is present between the floor system and unconditioned space.
Wrong - No air barrier is present between the floor system and unconditioned space.
Wrong - No air barrier is present between the floor system and unconditioned space.
View Image Download
Wrong - Plastic-covered blanket insulation that is installed directly against concrete walls with no rigid foam or closed-cell spray foam covering the concrete could trap moisture coming through the concrete, leading to mold, moisture, and odor problems.
Wrong - Plastic-covered blanket insulation that is installed directly against concrete walls with no rigid foam or closed-cell spray foam covering the concrete could trap moisture coming through the concrete, leading to mold, moisture, and odor problems.
Wrong - Plastic-covered blanket insulation that is installed directly against concrete walls with no rigid foam or closed-cell spray foam covering the concrete could trap moisture coming through the concrete, leading to mold, moisture, and odor problems.
View Image Download
Wrong - Sub-floor insulation has gaps, compression, and misalignment.
Wrong - Sub-floor insulation has gaps, compression, and misalignment.
Wrong - Sub-floor insulation has gaps, compression, and misalignment.
View Image Download
Wrong - Sub-floor insulation is not properly installed or supported.
Wrong - Sub-floor insulation is not properly installed or supported.
Wrong - Sub-floor insulation is not properly installed or supported.
View Image Download
Wrong - The basement blanket insulation is loosely attached to the interior of the basement wall, does not cover the entire wall, is not sealed at the edges, and is not installed over rigid foam that covers the entire surface of the foundation walls.
Wrong - The basement blanket insulation is loosely attached to the interior of the basement wall, does not cover the entire wall, is not sealed at the edges, and is not installed over rigid foam that covers the entire surface of the foundation walls.
Wrong - The basement blanket insulation is loosely attached to the interior of the basement wall, does not cover the entire wall, is not sealed at the edges, and is not installed over rigid foam that covers the entire surface of the foundation walls.
View Image Download
Wrong - The below-grade concrete does not have the correct construction to be impermeable to moisture because the lumber is untreated and against the concrete that lacks waterproofing.
Wrong - The below-grade concrete does not have the correct construction to be impermeable to moisture because the lumber is untreated and against the concrete that lacks waterproofing.
Wrong - The below-grade concrete does not have the correct construction to be impermeable to moisture because the lumber is untreated and against the concrete that lacks waterproofing.
View Image Download
Wrong - The fiberglass blanket insulation has no perforated vapor retarder, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
Wrong - The fiberglass blanket insulation has no perforated vapor retarder, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
Wrong - The fiberglass blanket insulation has no perforated vapor retarder, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
View Image Download
Wrong - This batt insulation is not aligned with the subfloor and joists.
Wrong - This batt insulation is not aligned with the subfloor and joists.
Wrong - This batt insulation is not aligned with the subfloor and joists.
View Image Download
Wrong - This plastic-covered blanket insulation is not perforated, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
Wrong - This plastic-covered blanket insulation is not perforated, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
Wrong - This plastic-covered blanket insulation is not perforated, does not cover the entire basement wall, is not sealed at the edges, and is not installed over rigid foam.
View Image Download
An uninsulated (or existing insulated) basement slab is retrofitted to reduce moisture transmission by sealing with epoxy paint.
An uninsulated (or existing insulated) basement slab is retrofitted to reduce moisture transmission by sealing with epoxy paint.
An uninsulated (or existing insulated) basement slab is retrofitted to reduce moisture transmission by sealing with epoxy paint.
View Image Download
Basement foundation insulated on interior with rigid foam.
Basement foundation insulated on interior with rigid foam.
Basement foundation insulated on interior with rigid foam.
View Image Download
Spray foam extends down the foundation wall to the slab, which has been retrofitted by adding dimple plastic drainage mat and rigid foam insulation.
Spray foam extends down the foundation wall to the slab, which has been retrofitted by adding dimple plastic drainage mat and rigid foam insulation.
Spray foam extends down the foundation wall to the slab, which has been retrofitted by adding dimple plastic drainage mat and rigid foam insulation.
View Image Download
Spray foam extends down the inside of the foundation wall to the uninsulated slab; because the wall lacked exterior perimeter drainage, the slab was cut and an interior footing drain was installed.
Spray foam extends down the inside of the foundation wall to the uninsulated slab; because the wall lacked exterior perimeter drainage, the slab was cut and an interior footing drain was installed.
Spray foam extends down the inside of the foundation wall to the uninsulated slab; because the wall lacked exterior perimeter drainage, the slab was cut and an interior footing drain was installed.
View Image Download
Spray foam insulation extends down the foundation wall to the slab, which has been retrofitted by cutting the slab to install drainage mat against the wall and a new perimeter footing drain, along with rigid foam plastic above the slab.
Spray foam insulation extends down the foundation wall to the slab, which has been retrofitted by cutting the slab to install drainage mat against the wall and a new perimeter footing drain, along with rigid foam plastic above the slab.
Spray foam insulation extends down the foundation wall to the slab, which has been retrofitted by cutting the slab to install drainage mat against the wall and a new perimeter footing drain, along with rigid foam plastic above the slab.
View Image Download
The basement is constructed with precast concrete walls lined with R-21.3 foil-faced rigid foam while an R-10 layer of XPS rigid foam covers the ground under the slab.
The basement is constructed with precast concrete walls lined with R-21.3 foil-faced rigid foam while an R-10 layer of XPS rigid foam covers the ground under the slab.
The basement is constructed with precast concrete walls lined with R-21.3 foil-faced rigid foam while an R-10 layer of XPS rigid foam covers the ground under the slab.
View Image Download
The basement walls are covered with a dimpled plastic water barrier then wrapped with 3 inches of XPS rigid foam with seams taped to keep out water.
The basement walls are covered with a dimpled plastic water barrier then wrapped with 3 inches of XPS rigid foam with seams taped to keep out water.
The basement walls are covered with a dimpled plastic water barrier then wrapped with 3 inches of XPS rigid foam with seams taped to keep out water.
View Image Download
The basement walls’ interior framing is set in 3 inches from the concrete to allow space for closed-cell foam that is sprayed directly on the concrete, then blown cellulose is added to fill the wall cavity.
The basement walls’ interior framing is set in 3 inches from the concrete to allow space for closed-cell foam that is sprayed directly on the concrete, then blown cellulose is added to fill the wall cavity.
The basement walls’ interior framing is set in 3 inches from the concrete to allow space for closed-cell foam that is sprayed directly on the concrete, then blown cellulose is added to fill the wall cavity.
View Image Download
The below-grade wall assembly includes dampproofing, draining details, and insulation.
The below-grade wall assembly includes dampproofing, draining details, and insulation.
The below-grade wall assembly includes dampproofing, draining details, and insulation.
View Image Download
The existing slab is retrofitted by coating with epoxy paint, then installing rigid foam insulation and a floating subfloor.
The existing slab is retrofitted by coating with epoxy paint, then installing rigid foam insulation and a floating subfloor.
The existing slab is retrofitted by coating with epoxy paint, then installing rigid foam insulation and a floating subfloor.
View Image Download
The existing slab is retrofitted with epoxy paint, rigid foam insulation, sleepers (furring strips), and subfloor.
The existing slab is retrofitted with epoxy paint, rigid foam insulation, sleepers (furring strips), and subfloor.
The existing slab is retrofitted with epoxy paint, rigid foam insulation, sleepers (furring strips), and subfloor.
View Image Download
The rim band connecting the insulated precast concrete basement walls to the floor joists above is spray foamed to provide air-sealing and insulation in this hard-to-seal juncture.
The rim band connecting the insulated precast concrete basement walls to the floor joists above is spray foamed to provide air-sealing and insulation in this hard-to-seal juncture.
The rim band connecting the insulated precast concrete basement walls to the floor joists above is spray foamed to provide air-sealing and insulation in this hard-to-seal juncture.
View Image Download
This basement is insulated on the exterior with rigid foam over dampproofing, with granular backfill and footing drains to facilitate drainage away from the foundation, a termite shield to protect from pests, and cellular PVC to protect the rigid foam.
This basement is insulated on the exterior with rigid foam over dampproofing, with granular backfill and footing drains to facilitate drainage away from the foundation, a termite shield to protect from pests, and cellular PVC to protect the rigid foam.
This basement is insulated on the exterior with rigid foam over dampproofing, with granular backfill and footing drains to facilitate drainage away from the foundation, a termite shield to protect from pests, and cellular PVC to protect the rigid foam.
View Image Download
This exterior insulated slab-on-grade monolithic grade beam foundation is protected from pests by termite shield at the sill plate, borate-treated framing, flashing at end of wall insulation, brick veneer over slab-edge insulation, and rock ground cover.
This exterior insulated slab-on-grade monolithic grade beam foundation is protected from pests by termite shield at the sill plate, borate-treated framing, flashing at end of wall insulation, brick veneer over slab-edge insulation, and rock ground cover.
This exterior insulated slab-on-grade monolithic grade beam foundation is protected from pests by termite shield at the sill plate, borate-treated framing, flashing at end of wall insulation, brick veneer over slab-edge insulation, and rock ground cover.
View Image Download
Presentations

Dry Basements: A Builder's Success Story

Author(s)
Gord Cooke
Organization(s)
Terra View Custom Homes,
EEBA
Publication Date
Webinar from Gord Cooke of Terra View Custom Homes on better basement and below grade construction practices to eliminate present and future moisture issues. Free EEBA login required.
Videos

Assembly Sequence for Concrete Wall with Exterior Insulation

Publication Date
Author(s)
University of Minnesota
Organization(s)
ORNL,
Oak Ridge National Laboratory,
University of Minnesota
Video animation showing an assembly sequence for a concrete basement wall with exterior insulation

How to Insulate a Basement

Publication Date
Author(s)
This Old House
Organization(s)
This Old House
Video describing how to warm up a chilly concrete wall with This Old House general contractor Tom Silva.

Radon Mitigation in New Construction

Publication Date
Author(s)
Benesch
Organization(s)
Cold Climate Housing Research Center,
CCHRC
Video describing radon precautions taken for a construction project in a high-risk radon area in Alaska.

UMN NorthernSTAR: DOE Building America: Exterior Foundation Insulation

Publication Date
Author(s)
University of Minnesota,
NorthernSTAR
Organization(s)
UMN,
NSTAR
Video describing an “excavationless” retrofit technique developed by the University of Minnesota to install exterior insulation around the foundation of an existing home by using high-pressure water to cut a trench through the dirt along the edge of a concrete foundation, remove the mud with a...
CAD
CAD Files
Foundation wall exterior board insulation with above-grade wall insulation
Foundation wall exterior board insulation with above-grade wall insulation
Foundation wall exterior board insulation with above-grade wall insulation
Download: DWG PDF
Foundation Wall Exterior board insulation without above-grade wall insulation
Foundation Wall Exterior board insulation without above-grade wall insulation
Foundation Wall Exterior board insulation without above-grade wall insulation
Download: DWG PDF
Spray foam on a stone or rubble foundation
Spray foam on a stone or rubble foundation
Spray foam on a stone or rubble foundation
Download: DWG PDF
Foundation wall interior rigid insulation with framed wall
Foundation wall interior rigid insulation with framed wall
Foundation wall interior rigid insulation with framed wall
Download: DWG PDF
Foundation wall interior rigid insulation with furring strips
Foundation wall interior rigid insulation with furring strips
Foundation wall interior rigid insulation with furring strips
Download: DWG PDF
Spray foam on concrete foundation wall with framed interior wall
Spray foam on concrete foundation wall with framed interior wall
Spray foam on concrete foundation wall with framed interior wall
Download: DWG PDF
Termite shield with exterior rigid foam above and below
Termite shield with exterior rigid foam above and below
Termite shield with exterior rigid foam above and below
Download: DWG PDF
Compliance

Compliance

ENERGY STAR New Homes and Apartments

DOE Zero Energy Ready Home

EPA Indoor airPLUS

International Energy Conservation Code (IECC)

International Residential Code (IRC)

Retrofit

SCOPE

Before considering basement insulation for an existing home, it’s critical to examine several health and durability factors including:

Only when these factors are examined (and any problems are addressed) should basement insulation be implemented. See the Success tab for more information on these topics, the Compliance tab for other resources, or the following Building America Solution Center guides for more information:

The U.S. Department of Energy’s Standard Work Specifications has additional information on basements and worker safety in basements.

More

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

Interior Foundation Insulation Upgrade - Madison Residence Madison, WI

Author(s)
Oak Ridge National Laboratory
Organization(s)
ORNL
Publication Date
Case study describing a basement retrofit of a 1916 home in Madison, Wisconsin that involved installing dimple drain mat and closed-cell spray foam on interior of basement wall and an interior footing drain to manage moisture before finishing an existing basement.

DOE ZERH HIA 2020 Case Study: Amaris Homes, Oakgreen Model, Afton, MN

Author(s)
Pacific Northwest National Laboratory,
U.S. Department of Energy
Organization(s)
DOE,
PNNL
Publication Date
Case study describing a DOE Zero Energy Ready Home 2020 Housing Innovation Award winning custom spec home in the cold climate that used a high efficiency 98 AFUE gas furnace, 5-stage 19 SEER heat pump, LED lighting, ENERGY STAR appliances, smart thermostats and lighting, and automated window blinds...
References and Resources*

Basement Insulation, Info 511

Author(s)
Building Science Corporation
Organization(s)
BSC
Publication Date
Information sheet describing techniques for insulating basements.

Basement Insulation Systems, BA-0202

Author(s)
Building Science Corporation
Organization(s)
BSC
Publication Date
Report describing approaches to insulating basements in homes built to meet Energy Star levels of performance of heat loss reduction.

Basement Insulation Technology Fact Sheet

Author(s)
Southface Energy Institute
Organization(s)
SEI,
Oak Ridge National Laboratory,
ORNL,
U.S. Department of Energy,
DOE
Publication Date
Fact sheet describing basement insulation considerations.

Fixing Wet Basements and Crawlspaces

Author(s)
Todd Jason
Organization(s)
Home Energy Magazine
Publication Date
Article describing methods to manage moisture, rainwater, and vapor in basements and crawlspaces.

Foundation Design Handbook

Author(s)
Carmody John,
Mosiman Garrett,
Handeen Daniel,
Huelman Patrick H,
Christian Jeffrey E
Organization(s)
Oak Ridge National Laboratory,
ORNL,
University of Minnesota
Publication Date
Handbook providing guidance on the design and construction of foundations for homes, including insulation, air sealing, and water management details for basements, crawlspaces, and slabs.

How to Insulate a Basement Wall

Author(s)
Holladay Martin
Organization(s)
Green Building Advisor,
GBA
Publication Date
Blog entry describing methods for insulating basement walls on the interior or exterior.

How to Insulate Your Basement

Author(s)
Mathews Erin
Organization(s)
This Old House
Publication Date
An article and video of a breakdown on the preparation and installation of basement insulation.

How to Seal Up to Prevent Rodent Infestations

Author(s)
Centers for Disease Control and Prevention
Organization(s)
CDC
Publication Date
A website providing a checklist of important areas to check when sealing holes inside and outside of the home to prevent entry by rodents and other outside pests.

Measure Guideline: Basement Insulation Basics

Author(s)
Aldrich Robb,
Mantha Pallavi,
Puttagunta Srikanth
Organization(s)
Consortium for Advanced Residential Buildings,
CARB,
National Renewable Energy Laboratory,
NREL,
Steven Winter Associates,
SWA
Publication Date
Document describing good practices for insulating basements in new and existing homes.

Pest Prevention by Design: Authoritative Guidelines for Designing Pests out of Structures

Author(s)
Geiger Chris A,
Cox Caroline
Organization(s)
San Francisco Department of the Environment,
SF Environment,
Center for Environmental Health,
CEH,
International Code Council,
ICC
Publication Date
Report providing detailed steps for builders, architects, and property managers to take for integrated pest management for control of a variety of pests including insects, rodents, and birds.

Understanding Basements, BSD-103

Author(s)
Lstiburek Joseph W
Organization(s)
Building Science Corporation,
BSC
Publication Date
Information sheet with methods for constructing or retrofitting basements to reduce moisture issues.

Why We Need to Know More About Basement Moisture

Author(s)
Cheple Marilou,
Huelman Patrick H
Organization(s)
University of Minnesota,
UMN,
American Society of Heating Refrigerating and Air-Conditioning Engineers,
ASHRAE,
NorthernSTAR,
NSTAR,
Oak Ridge National Laboratory,
ORNL
Publication Date
Conference paper presented at the 8th International Conference on Thermal Performance of Exterior Envelopes of Whole Buildings describing moisture from basements and crawlspaces as a source of indoor humidity and providing recommendations for finishing below-grade spaces to limit potential indoor...
*For non-dated media, such as websites, the date listed is the date accessed.
Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Steven Winter Associates, Inc. www.swinter.com

Sales
Print
Building Science-to-Sales Translator

Foundation Wall Water/Damp-Proofing = Foundation Wall Water Barrier

Technical Description

Porous concrete foundations should be treated to avoid water seepage into the home. Builders treat below-grade walls with a damp-proof coating such as an asphalt emulsion. For more reiorous protection, a plastic drainage plane may be used instead of, or in addition to, the damp proof coating.  This surface coating may be joined by a layer of insulation. Rigid fiberglass allows water to drain through it; rigid polyurethane foam rated for soil contact is another option. A gravel layer is added to provide a good backfill for draining. This allows water to flow through the gravel toward the foundation footing where a perforated drain pipe will carry it away from the structure.

Alternate Terms

Dry-by-Design Foundation Wall
Foundation Floor Water Barrier Technology
Professionally-Installed Foundation Water Barrier
Foundation Wall Water Barrier
Sales Message

Foundation wall water barriers help drain water away from the below-grade walls. What this means to you is peace-of-mind knowing your home has a comprehensive set of measures that minimize the risk of water damage in your basement. Wouldn’t you agree every home should have full water protection?

Last Updated

Did you find this information helpful?

If you have questions and/or would like a reply to this feedback, please include your e-mail address in the message.
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.