Spray Foam Interior Insulation for Existing Foundation Walls

Scope Images
Closed-cell spray foam was applied to the interior of a foundation wall
Closed-cell spray foam was applied to the interior of a foundation wall
Scope

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 Certified Homes, and Indoor airPLUS.

Description

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”, “Exterior Surface of Below-Grade Walls”, “Final Grade”, “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 Sill Plates.

Closed-cell spray foam is used to retrofit an existing rubble basement foundation wall
Figure 1. Closed-cell spray foam is used to retrofit an existing rubble basement foundation wall. The spray foam also insulates the sill beam, fills the floor joist cavity at the rim joist, and fills the base of the wall cavity because the wall is balloon framed.
Spray foam extends down the inside of the foundation wall to the uninsulated slab
Figure 2. 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 foundation wall to the slab, which has been retrofitted by adding dimple plastic drainage mat and, rigid foam insulation
Figure 3. 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 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
Figure 4. 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.

How to Install Spray Foam Insulation at Foundation Wall

  1. 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.
  2. 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.
  3. 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.

Ensuring Success

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.

Climate

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. 

Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18.
Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18. (Source: 2012 IECC)

 

Climate Zone Map from IECC 2021.
Figure 2. Climate Zone Map from IECC 2021. (Source: 2021 IECC)

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.

Minimum R-Value Requirements for Slab Insulation in the 2009 and 2012 IECC
Table 1. Minimum R-Value Requirements for Slab Insulation in the 2009 and 2012 IECC
CAD

Compliance

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 Certified Homes, Version 3/3.1 (Rev. 09)

ENERGY STAR Certified 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.

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 levels4, 5, 6 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 4d, AND specified home infiltration does not exceed the following:5, 6

  • 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 conditioned space.26,27

Water Management System Builder Requirements

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 pump. If drain tile is on interior side of footing, then channel provided through footing to exterior side.8

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 Minimum Insulation Requirements: 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 International Energy Conservation Code (IECC)

Section 401.3 Certificate

Section 402.1.1 Insulation and fenestration criteria

Table 402.1.1 Insulation and Fenestration Requirements by Component

Table 402.1.3 Equivalent U-factors

Section 402.2.7 Basement walls

Table 402.4.2 Air barrier and insulation inspection component criteria

2012 IECC

Section R401.3 Certificate

Section R402.1.1 Insulation and fenestration criteria

Table R402.1.1 Insulation and Fenestration Requirements by Component

Table R402.1.3 Equivalent U-factors

Section R402.2.8 Basement walls

Table R402.4.1.1 Air barrier and insulation installation

2015 and 2018 IECC

Section R401.3 Certificate

Section R402.1.2 Insulation and fenestration criteria

Table R402.1.2 Insulation and Fenestration Requirements by Component

Table R402.1.4 Equivalent U-factors

Section R402.2.9 Basement walls

Table R402.4.1.1 Air barrier and insulation installation

Retrofit: 

2009, 2012, 2015, 2018, and 2021 IECC

Section R101.4.3 (Section R501.1.1 in 2015, 2018, and 2021 IECC). 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.)

2009 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 N1101.4 Building thermal envelope insulation

Section N1101.9 Certificate

Section N1102.1 Insulation and fenestration criteria

Table N1102.1 Insulation and fenestration requirements by component

Table N1102.1.2 Equivalent U-factors

Section N1102.2.7 Basement walls

Table N1102.4.2 Air barrier and insulation inspection

2012 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 N1101.12.1 (R303.1.1) Building thermal envelope insulation

Section N1101.16 (R401.3) Certificate (Mandatory)

Section N1102.1.1 (R402.1.1) Insulation and fenestration criteria

Table N1102.1.1 (R402.1.1) Insulation and fenestration requirements by component

Table N1102.1.3 (R402.1.3) Equivalent U-factors

Section N1102.2.8 (R402.2.8) Basement walls

Table N1102.4.1.1 (402.4.1.1) Air barrier and insulation inspection

2015 and 2018 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 (R303.1.1) Building thermal envelope insulation

Section N1101.14 (R401.3) Certificate (Mandatory)

Section N1102.1.2 (R402.1.1) Insulation and fenestration criteria

Table N1102.1.2 (R402.1.1) Insulation and fenestration requirements by component

Table N1102.1.4 (R402.1.4) Equivalent U-factors

Section N1102.2.9 (R402.2.9) Basement walls

Table N1102.4.1.1 (402.4.1.1) Air barrier and insulation inspection

Retrofit: 

 

2009, 2012, 20152018, and 2021 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018, N1109.1 in 2021 IRC). 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.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

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
References and Resources*
Author(s)
Pettit,
Neuhauser,
Gates
Organization(s)
Building Science Corporation
Publication Date
Description
Guidebook providing useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate.
*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.

Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team

Building Science Measures
Building Science-to-Sales Translator

High-R Foundation Insulation = High-Efficiency or Ultra-Efficient Foundation Insulation

Image(s)
Technical Description

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.

High-Efficiency or Ultra-Efficient Foundation Insulation
Sales Message

High-efficiency foundation insulation helps provide added thermal protection. What this means to you is less wasted energy along with enhanced comfort and quiet. Knowing there is one opportunity to optimize performance during construction, wouldn’t you agree it’s a great opportunity to meet or exceed future codes?

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