Insulate a foundation wall by adding spray foam insulation to the interior side as follows:
- Inspect the existing foundation wall for any deficiencies and make any necessary corrections including fixing any water intrusion or moisture issues in the basement, crawlspace or along the foundation wall, prior to commencing the retrofit work.
- Install closed-cell spray foam insulation along the inside of the foundation wall and sill beam to the minimum thermal levels specified in the current adopted building code.
- Apply thermal/ignition barrier as required by the current adopted building code.
For more on slab foundations, see the U.S. Department of Energy’s Standard Work Specifications.
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Single-Family New Homes, and Indoor airPLUS.
In most existing houses, the basement or crawlspace walls are uninsulated. One method for insulating the walls is to cover the interior surface with spray foam.
Most homes have foundation walls made of concrete (cast concrete or concrete block) or constructed of irregular discrete pieces, such as fieldstone, brick, or rubble. The primary distinctions between these foundation types is the character of the surface of the wall – either a flat surface or an irregular surface – and the water permeability of the wall, which is quite high for walls built of irregular discrete pieces. The use of spray foam interior insulation is appropriate for either type.
Measures should be taken to protect foundation walls from bulk water (even if they are not being insulated). If the grade around the perimeter does not slope away from the house, make grading adjustments so that it slopes away at 5% grade for at least the first 3 feet and if possible, 10 feet. If gutters are installed, the downspouts must direct water away from the perimeter of the house and the gutter system must be regularly maintained to prevent overflowing, leaks, or breaks in the system because these can concentrate water along the building foundation. Another protective measure is to provide a trench of gravel around the perimeter that extends out at least as far as the roof drip edge. This helps disperse bulk water that comes from the roof so that the top of the foundation wall is not continually splashed. It is especially important to keep bulk water away from the exposed part of stone or brick foundation walls to reduce the impacts of freeze-thaw cycles.
If necessary, a perimeter drainage system can be installed around the building’s exterior or interior (see Figure 2). For additional guidance on foundation drainage and moisture management see the guides “Drain or Sump Pump Installed in Basements or Crawlspaces”, “Damp-Proof Exterior Surface of Below-Grade Walls”, “Final Grade Slopes Away from Walls”, “Water Management of Existing Crawlspace Floor”
Before proceeding with the foundation wall retrofit, an assessment should be made of the condition of the sill plate or sill beam, which sits on top of the foundation wall. If there is no capillary break under the sill and/or if the sill is within 12 inches of the ground, it is possible that it has suffered water damage. If so, the damaged pieces should be replaced and at the same time, a capillary break should be installed under the new pieces. If there is no capillary break under the sill and/or the sill is within 12 inches of the ground, but there is no indication of damage, then it is likely that the sill has been able to dry. However, covering the sill, rim joist, and wall with spray foam will limit the ability of the sill to dry to the interior, so special treatment may be required at the base of the exterior wall. (See the guide “Flashing at Bottom of Exterior Walls” for additional information.)
It is recommended that the seams in the sill plate framing be caulked prior to insulating. For more guidance, see Air Sealing Sill Plates.
How to Install Spray Foam Insulation at Foundation Wall
- Inspect the existing foundation wall for any deficiencies. Make any necessary repairs prior to beginning the retrofit work. For stone or brick walls, take measures to protect the exposed part of the foundation wall from bulk water if necessary, such as grading the soil surface away from the structure, installing gutters and downspouts, and installing a footing drain.
- Install closed-cell spray foam insulation at the foundation wall to at least the minimum levels specified in the local building code. Extend the spray foam over the sill beam. If the house has balloon framing, use spray foam insulation to fill the base of the wall cavity above the top of the foundation to air seal it to the back side of the existing wall sheathing, as shown in Figure 1.
- Apply a spray-on thermal/ignition barrier as required by the local code.
ALTERNATELY, build a perimeter stud wall on the interior side of the spray foam. Don’t insulate the stud wall. Cover it with non-paper-faced gypsum board as the thermal/ignition barrier on the interior side. If metal studs are used for the interior wall, do not insulate it unless the metal studs are placed at least 1 inch to the interior side of the foundation wall insulation.
Provide a continuous layer of spray foam insulation extending from the base of the wall cavity above down to the basement slab.
Manage bulk and capillary water prior to the insulation/air seal retrofit.
Provide a thermal/ignition barrier as required by the current adopted building code.
The basement wall assembly should be designed for a specific hygrothermal region, rain exposure zone, and interior climate.
The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide.
The insulation levels should be based on the minimum requirements for vapor control in the current adopted building code and the minimum requirements for thermal control in the current energy code. Additional insulation can be added above these minimums to create high R-value basement wall assemblies. The table below provides the minimum thermal resistance (R-value) requirements for basement walls specified in the 2009 IECC (ICC 2009b) and the 2012 IECC (ICC 2012b), based on climate zone.
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which 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.
ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)
ENERGY STAR Single-Family New Homes requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009 International Energy Conservation Code (IECC) with some alternatives and exceptions, and achieve Grade 1 installation per RESNET Standards (see 2009 and 2012 IECC Code Level Insulation – ENERGY STAR Requirements and Insulation Installation (RESNET Grade 1). If the state or local residential building energy code requires higher insulation levels than those specified in the 2009 IECC, you must meet or exceed the locally mandated requirements. Some states have adopted the 2012 or 2015 IECC. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state.
National Rater Design Review Checklist
3. High-Performance Insulation.
3.1 Specified ceiling, wall, floor, and slab insulation levels comply with one of the following options:
3.1.1 Meets or exceeds 2009 IECC levels5, 6, 7 OR;
3.1.2 Achieves ≤ 133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, per guidance in Footnote 5d, AND specified home infiltration does not exceed the following:6, 7
- 3 ACH50 in CZs 1, 2
- 2.5 ACH50 in CZs 3, 4
- 2 ACH50 in CZs 5, 6, 7
- 1.5 ACH50 in CZ 8
4. Air Sealing (Unless otherwise noted below, “sealed” indicates the use of caulk, foam, or equivalent material).
4.3 Above-grade sill plates adjacent to conditioned space sealed to foundation or sub-floor. Gasket also placed beneath above-grade sill plate if resting atop concrete / masonry & adjacent to cond. space.27, 28
Footnote 5) Specified levels shall meet or exceed the component insulation levels in 2009 IECC Table 402.1.1. The following exceptions apply:
a. Steel-frame ceilings, walls, and floors shall meet the insulation levels of 2009 IECC Table 402.2.5. In CZ 1 and 2, the continuous insulation requirements in this table shall be permitted to be reduced to R-3 for steel-frame wall assemblies with studs spaced at 24 in. on center. This exception shall not apply if the alternative calculations in d) are used;
b. For ceilings with attic spaces, R-30 shall satisfy the requirement for R-38 and R-38 shall satisfy the requirement for R-49 wherever the full height of uncompressed insulation at the lower R-value extends over the wall top plate at the eaves. This exemption shall not apply if the alternative calculations in d) are used;
c. For ceilings without attic spaces, R-30 shall satisfy the requirement for any required value above R-30 if the design of the roof / ceiling assembly does not provide sufficient space for the required insulation value. This exemption shall be limited to 500 sq. ft. or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in d) are used;
d. An alternative equivalent U-factor or total UA calculation may also be used to demonstrate compliance, as follows: An assembly with a U-factor equal or less than specified in 2009 IECC Table 402.1.3 complies. A total building thermal envelope UA that is less than or equal to the total UA resulting from the U-factors in Table 402.1.3 also complies. The performance of all components (i.e., ceilings, walls, floors, slabs, and fenestration) can be traded off using the UA approach. Note that Items 3.1 through 3.3 of the National Rater Field Checklist shall be met regardless of the UA tradeoffs calculated. The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The calculation for a steel-frame envelope assembly shall use the ASHRAE zone method or a method providing equivalent results, and not a series-parallel path calculation method.
Footnote 6) Consistent with the 2009 IECC, slab edge insulation is only required for slab-on-grade floors with a floor surface less than 12 inches below grade. Slab insulation shall extend to the top of the slab to provide a complete thermal break. If the top edge of the insulation is installed between the exterior wall and the edge of the interior slab, it shall be permitted to be cut at a 45-degree angle away from the exterior wall. Alternatively, the thermal break is permitted to be created using ≥ R-3 rigid insulation on top of an existing slab (e.g., in a home undergoing a gut rehabilitation). In such cases, up to 10% of the slab surface is permitted to not be insulated (e.g., for sleepers, for sill plates). Insulation installed on top of slab shall be covered by a durable floor surface (e.g., hardwood, tile, carpet).
Footnote 7) Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, slab insulation shall also be installed at this interface to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this requirement, partners shall provide the detail to EPA to request an exemption prior to the home’s certification. EPA will compile exempted details and work with industry to develop feasible details for use in future revisions to the program. A list of currently exempted details is available at: energystar.gov/slabedge.
Footnote 27) Existing sill plates (e.g., in a home undergoing a gut rehabilitation) on the interior side of structural masonry or monolithic walls are exempt from this Item. In addition, other existing sill plates resting atop concrete or masonry and adjacent to conditioned space are permitted, in lieu of using a gasket, to be sealed with caulk, foam, or equivalent material at both the interior seam between the sill plate and the subfloor and the seam between the top of the sill plate and the sheathing.
Footnote 28) In Climate Zones 1 through 3, a continuous stucco cladding system adjacent to sill and bottom plates is permitted to be used in lieu of sealing plates to foundation or sub-floor with caulk, foam, or equivalent material.
National Water Management System Builder Requirements
1. Water-Managed Site and Foundation.
1.8 Drain tile installed at basement and crawlspace walls, with the top of the drain tile pipe below the bottom of the concrete slab or crawlspace floor. Drain tile surrounded with ≥ 6 in. of ½ to ¾ in. washed or clean gravel and with gravel layer fully wrapped with fabric cloth. Drain tile level or sloped to discharge to outside grade (daylight) or to a sump pit with a pump. If drain tile is on interior side of footing, then channel provided through footing to exterior side.9
Footnote 9) Alternatively, either a drain tile that is pre-wrapped with a fabric filter or a Composite Foundation Drainage System (CFDS) that has been evaluated by ICC-ES per AC 243 are permitted to be used. Note that the CFDS must include a soil strip drain or another ICC-ES evaluated perimeter drainage system to be eligible for use. In an existing home (e.g., in a home undergoing a gut rehab.) a drain tile installed only on the interior side of the footing without a channel is permitted. Additionally, a drain tile is not required when a certified hydrologist, soil scientist, or engineer has determined that a crawlspace foundation, or an existing basement foundation (e.g., in a home undergoing a gut rehab.), is installed in Group I Soils (i.e. well-drained ground or sand-gravel mixtures), as defined by 2009 IRC Table R405.1.
Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in your state.
DOE Zero Energy Ready Home (Revision 07)
The DOE Zero Energy Ready Home Program is a voluntary high-performance home labeling program for new homes operated by the U.S. Department of Energy. Builders and remodelers who are conducting retrofits are welcome to seek certification for existing homes through this voluntary program.
Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Exhibit 2, Item 2) Ceiling, wall, floor, and slab insulation shall meet or exceed 2015 IECC levels and achieve Grade 1 installation, per RESNET standards.
Exhibit 1, Item 6) Certified under EPA Indoor airPLUS.
EPA Indoor airPLUS (Revision 04)
1.4 Basement and Crawlspace Insulation and Conditioned Air.
- Seal crawlspace and basement perimeter walls to prevent outside air infiltration.
- Insulate crawlspace and basement perimeter walls according to the prescriptive values determined by local code or R-5, whichever is greater.
- Provide conditioned air at a rate not less than 1 cfm per 50 sq. ft. of horizontal floor area. This can be achieved by a dedicated supply (2015 IRC section R408.3.2.2) or through crawl-space exhaust (2015 IRC section R408.3.2.1). However, if radon-resistant features are required (see Specification 2.1), do not use the crawlspace exhaust method.
See Indoor airPLUS Specifications for exceptions.
2009-2021 IECC and IRC Insulation Requirements Table
The minimum insulation requirements for ceilings, walls, floors, and foundations in new homes, as listed in the 2009, 2012, 2015, 2018, and 2021 IECC and IRC, can be found in this table.
2009, 2012, 2015, 2018, and 2021 International Energy Conservation Code (IECC)
Section R401.3 Certificate
Section R402.1.2 Insulation and fenestration criteria
Table R402.1.2 (402.1.1 in 2009 and 2012 IRC) Insulation and fenestration requirements by component
Table R402.1.4 (402.1.3 in 2009 and 2012 IRC) R-value Computation
Section R402.4 Air leakage (Mandatory)
Table R402.4.1.1 (402.4.2 in 2009 IRC) Air barrier and insulation installation
Retrofit: 2009, 2012, 2015, 2018, and 2021 IECC
Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)
Chapter 5 (in 2015, 2018, 2021). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.
2009, 2012, 2015, 2018, and 2021 International Residential Code (IRC)
Section R401.3 Drainage
Section R403.1.4.1 Frost protection
Section R403.1.6 Foundation anchorage
Section R403.3 Frost protected shallow foundations
Section R403.3.4 Termite damage
Section R404.1.4.2 Concrete foundation walls
Section R405 Foundation drainage
Section R406 Foundation waterproofing and dampproofing
Section N1101.10.1 (N1101.12.1 in 2012 and N1101.4 in 2009 IRC) Building thermal envelope insulation
Section N1101.14 (N1101.16 in 2012 and N1101.9 in 2009 IRC) Certificate (Mandatory)
Section N1102.1.2 (N1102.1.1 in 2012 and N1102.1 in 2009 IRC) Insulation and fenestration criteria
Table N1102.1.2 (N1102.1.1 in 2012 and N1102.1 in 2009 IRC) Insulation and fenestration requirements by component
Table N1102.1.4 (N1102.1.3 in 2012 and N1102.1. in 2009 IRC) Equivalent U-factors or R-value Computation
Section N1102.2.9 (N1102.2.8 in 2012 and 2021 and N1102.2.7 in 2009 IRC) Basement walls
Table N1184.108.40.206 (N1102.4.2 in 2009 IRC) Air barrier and insulation inspection
Retrofit: 2009, 2012, 2015, 2018, and 2021 IRC
Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)
Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.
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.
Existing Whole-House Solutions Case Study: 56th and Walnut: A Philly Gut Rehab Development, Philadelphia, Pennsylvania
Existing Whole-House Solutions Case Study: Multifamily Individual Heating and Ventilation Systems, Lawrence, Massachusetts
Existing Whole-House Solutions Case Study: National Grid Deep Energy Retrofit Pilot Program - Clark Residence
The following authors and organizations contributed to the content in this Guide.
Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team
High-R Foundation Insulation = High-Efficiency or Ultra-Efficient Foundation Insulation
There are two levels of foundation insulation: high-efficiency insulation, which meets the 2015 International Energy Conservation Code, and ultra-efficient insulation, which is 25% more efficient than this national code. Using high-efficiency and ultra-efficient insulation, along with professional installation (e.g., no gaps, voids, compression, or misalignment with air barriers; complete air barriers; and minimal thermal bridging) creates conditioned spaces that require very little heating and cooling, along with, even comfort and quiet throughout the house.