Log in or register to create Field Kits and Sales Worksheets. Why register?

Spray Foam Insulation Applied over the Siding of Existing Exterior Walls

Scope

Spray foam is installed between new studs over the existing siding in this deep energy retrofit
Spray foam is installed between new studs over the existing siding in this deep energy retrofit

Install spray foam on the exterior of the existing home after framing over the existing siding. Then install new siding over the new studs and spray foam for this deep energy retrofit technique.

In this design, add exterior spray foam insulation with stand-off furring. The design includes a 2x6 ledger board at the bottom and top of the wall, as well as 2x4 studs that are installed on edge to provide wall cavities that can hold a 3 inch layer of spray foam applied to the exterior face of the existing wall. New windows are installed, as well as new siding on top of the insulation. In addition, extruded polystyrene (XPS) is installed in the interior of the foundation walls and spray foam insulation is added to the attic space.

This retrofit measure requires a crew that can perform a number of different tasks (e.g., framing, flashing, window install, trim carpentry). Because of the project sequencing, this project does not lend itself to piecemeal subcontracting various tasks (e.g., framing subcontractor, window installer, drainage plane installer, trim carpenter).

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

One method to significantly increase the insulation level of an existing home without sacrificing interior space is to install spray foam insulation on the exterior of the home. This measure involves installing 2x4 studs over the existing siding. The 2x4s are held slightly away from the wall with metal clips so that when the spray is applied to fill the new 2x4 wall cavities, it can fill in between the 2x4s and the existing walls (see Figure 1). The advantages of this strategy include using spray foam to encapsulate existing siding materials that might include lead paint, reducing the thermal bridging or transfer of heat through the existing wall studs, and creating a vented rain screen assembly to promote drying.

This strategy might be considered by homeowners who are already considering replacing siding or windows or who are conducting some other exterior upgrade.

Deep energy retrofit showing insulation sprayed on exterior of walls over existing siding
Figure 1. Deep energy retrofit showing insulation sprayed on exterior of walls over existing siding. (Image courtesy of IBACOS).

In a field study conducted by IBACOS in New York (see Figure 2), the exterior spray foam strategy was designed, implemented in a test facility to determine techniques for working around wall penetrations like wiring and doors, then installed on site in an actual home. Results from the field study (Herk and Poerschke 2015) found this strategy achieved the following energy-related targets:

  • Whole-house air leakage improvements that can approach or be lower than 0.25 CFM 50/shell square foot (SSF) upon completion.
  • Center of wall R-value of approximately R-25.
  • An exterior wall insulation retrofit strategy that can be accomplished for approximately $12 to $18 per SSF. This includes the installation of new wall framing and the removal/installation of windows, window trim, insulation, and bug screen. Siding was a cost that is not included in this number.

Although it is likely that this retrofit technique can be applied to most siding types, at this time, research has not been done to determine the suitability of the application on brick or stone siding.

Retrofit spray foam over existing walls showing design, testing, and final construction
Figure 2. Retrofit spray foam over existing walls showing design, testing, and final construction. (Image courtesy of IBACOS).

How to Install Spray Foam Insulation on Existing Walls

  1. Assess the existing condition of the wall. (See Figure 3.) Be sure to look for and make note of loose or crooked siding. These types of siding imperfections could lead to an uneven ledger board or stud, which then could result in a wavy siding application.
    Assess the existing condition of the wall
    Figure 3.  Assess the existing condition of the wall. (Image courtesy of IBACOS).

  2. Remove the existing window trim and fasten the ledger boards through the existing exterior cladding and sheathing. (See Figure 4.) If the existing wall surface is uneven, shim the ledger boards if necessary to keep the new framing and any doors and windows that will be installed a uniform distance from the existing wall.
    Remove the existing window trim and fasten the ledger boards through the existing exterior cladding and sheathing
    Figure 4. Remove the existing window trim and fasten the ledger boards through the existing exterior cladding and sheathing. (Image courtesy of IBACOS).

  3. Attach metal “L” clips on the top and bottom ledger board—one on either side of where a new vertical 2x4 will be attached. (See Figure 5.) Remove the existing window and install new framing for the new window.
    Attach metal “L” clips on the top and bottom ledger board for new vertical 2x4s
    Figure 5. Attach metal “L” clips on the top and bottom ledger board for new vertical 2x4s. (Image courtesy of IBACOS).

  4. Install the vertical 2x4s, spaced as needed based on structural calculations and siding manufacturer requirements. These are attached to the ledger boards using the metal “L” clips and they create a framework to hold the spray foam. (See Figures 6 and 7.)
    Install the vertical 2x4s, spaced as needed based on structural calculations and siding manufacturer requirements
    Figure 6. Install the vertical 2x4s, spaced as needed based on structural calculations and siding manufacturer requirements. (Image courtesy of IBACOS).

    Ledger board, metal brackets, and vertical 2x4s have been installed in preparation for exterior spray foam in this retrofit exterior wall insulation technique
    Figure 7. Ledger board, metal brackets, and vertical 2x4s have been installed in preparation for exterior spray foam in this retrofit exterior wall insulation technique. (Image courtesy of IBACOS).

  5. Install two horizontal framing members on the top and bottom of the rough opening for the new window. Slightly slope the sill framing to the exterior. (See Figure 8.)
    Install two horizontal framing members on the top and bottom of the rough opening for the new window
    Figure 8. Install two horizontal framing members on the top and bottom of the rough opening for the new window. Slightly slope the sill framing to the exterior.  (Image courtesy of IBACOS).

  6. Install the sill pan in the window frame. (See Figure 9.)
    Install the sill pan in the window frame
    Figure 9. Install the sill pan in the window frame. (Image courtesy of IBACOS).

  7. Install flexible flashing over the sill pan and at least 6 inches up the sides of the jamb. (See Figure 10.)
    Install the flexible flashing over the sill pan and at least 6 inches up the sides of the jamb
    Figure 10. Install the flexible flashing over the sill pan and at least 6 inches up the sides of the jamb. (Image courtesy of IBACOS).

  8. Install caulk on the face of the rough opening at the jambs and head. Do not caulk the sill. (See Figure 11.)
    Install caulk on the face of the rough opening at the jambs and head. Do not caulk the sill
    Figure 11. Install caulk on the face of the rough opening at the jambs and head. Do not caulk the sill. (Image courtesy of IBACOS).

  9. Install the new window or re-install the old window. (See Figures 12 and 13.)
    Install the new window
    Figure 12. Install the new window. (Image courtesy of IBACOS).

    Windows are installed in new framing in preparation for adding exterior spray foam insulation
    Figure 13. Windows are installed in new framing in preparation for adding exterior spray foam insulation. (Image courtesy of IBACOS).

  10. Install the jamb flashing (flat on the face of the window flange). (See Figure 14.)
    Install the jamb flashing (flat on the face of the window flange)
    Figure 14. Install the jamb flashing (flat on the face of the window flange). (Image courtesy of IBACOS).

  11. Install the head flashing from the face of the existing wall to lap over the head of the new window. Also, tape the flashing at the head using straight flashing tape lapped over the horizontal part of the head framing. (See Figure 15.)
    Install head flashing from the face of the existing wall to lap over the head of the new window
    Figure 15. Install head flashing from the face of the existing wall to lap over the head of the new window. (Image courtesy of IBACOS).

  12. Install the vertical framing members above and below the new window, and install the insect screen to the bottom of the new wall. Air seal the window from the interior using non-expanding foam sealant and install internal jamb extensions to prevent exterior spray foam from getting into the house. (See Figure 16.) Cover the windows and exposed foundation with plastic to minimize the possibility of damage due to overspraying with the spray foam.
    Install the vertical framing members above and below the new window, and install the insect screen to the bottom of the new wall
    Figure 16. Install the vertical framing members above and below the new window, and install the insect screen to the bottom of the new wall. (Image courtesy of IBACOS).

    First spray foam along the inside edges of each vertical 2x4 to “picture frame” the area
    Figure 17. First spray foam along the inside edges of each vertical 2x4 to “picture frame” the area. (Image courtesy of IBACOS).

  13. Spray insulation within the cavities of the new wall. (See Figure 18.)
    Spray insulation within the cavities of the new wall
    Figure 18. Spray insulation within the cavities of the new wall. (Image courtesy of IBACOS).

  14. Install the new cladding and install the new window trim. (See Figure 19.)
    Install the new cladding and install the new window trim
    Figure 19. Install the new cladding and install the new window trim. (Image courtesy of IBACOS).

 

Ensuring Success

  • Cover the windows and exposed foundation with plastic to protect against foam overspray.
  • Use extra metal clips or picture frame spraying technique to keep studs in place while installing spray foam in new stud cavities.
  • For efficiency, hire one contractor or crew that can perform most or all of the tasks involved in this retrofit measure (e.g., framing, flashing, window install, trim carpentry).

Climate

No climate specific information applies.

Training

Right and Wrong Images

None Available

Presentations

None Available

Videos

None Available

CAD Images

None Available

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

[Guidance for Version 3.0, Rev 08 is coming soon.]

ENERGY STAR Certified Homes is a voluntary high-performance home labeling program for new homes operated by the U.S. Department of Energy and the U.S. Environmental Protection Agency. Builders and remodelers who are conducting retrofits are welcome to seek certification for existing homes through this voluntary program.

ENERGY STAR Certified Homes (Version 3.0, Rev. 07) requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009 International Energy Conservation Code (IECC).

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 IECC. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state. For states that have adopted the 2012 IECC or an equivalent code, EPA intends to implement the ENERGY STAR Certified Homes Version 3.1 National Program Requirements for homes permitted starting one year after state-level implementation of the 2012 IECC or an equivalent code. However, EPA will make a final determination of the implementation timeline on a state-by-state basis. Some states and regions of the country have ENERGY STAR requirements that differ from the national requirements. Visit ENERGY STAR’s Regional Specifications page for more information on those region-specific requirements.

The ENERGY STAR Thermal Enclosure System Rater Checklist (Ver 3, Rev 07) specifies:

2.1 Ceiling, wall, floor and slab insulation levels shall comply with one of the following options:

2.1.1 Meet or exceed 2009 IECC levels, 3,4,5 OR

2.1.2 Achieve <= 133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, excluding fenestration and per guidance in note “d” below, AND home shall achieve <= 50% of the infiltration rate in Exhibit 1 of the National Program Requirements. 4,5

(3) Insulation levels in a home shall meet or exceed the component insulation requirements in the 2009 IECC - Table 402.1.1. The following exceptions apply:

Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 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 inch on center. This exception shall not apply if the alternative calculations in "d" below are used;

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;

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 square feet or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in "d" are used;

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 insulation levels of all non-fenestration components (i.e., ceilings, walls, floors, and slabs) can be traded off using the UA approach under both the Prescriptive and the Performance Path. Note that fenestration products (i.e., windows, skylights, doors) shall not be included in this calculation. Also, note that while ceiling and slab insulation can be included in trade-off calculations, the R-value must meet or exceed the minimum values listed in Items 4.1 through 4.3 of the ENERGY STAR Checklist to provide an effective thermal break, 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.

(4) 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.

(5) 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 qualification. 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: www.energystar.gov/slabedge.

2.2 All ceiling, wall, floor, and slab insulation shall achieve RESNET-defined Grade I installation or, alternatively, Grade II for surfaces that contain a layer of continuous, air impermeable insulation ≥ R-3 in Climate Zones 1 to 4, ≥ R-5 in Climate Zones 5 to 8

3 Fully-Aligned Air Barriers. At each insulated location noted below, a complete air barrier shall be provided that is fully aligned with the insulation as follows:

At interior or exterior surface of ceilings in Climate Zones 1-3; at interior surface of ceilings in Climate Zones 4-8. Also, include barrier at interior edge of attic eave in all climate zones using a wind baffle that extends to the full height of the insulation. Include a baffle in every bay or a tabbed baffle in each bay with a soffit vent that will also prevent wind washing of insulation in adjacent bays

At exterior surface of walls in all climate zones; and also at interior surface of walls for Climate Zones 4-8 7

At interior surface of floors in all climate zones, including supports to ensure permanent contact and blocking at exposed edge

3.1.8 Garage rim / band joist adjoining conditioned space

3.1.9 All other exterior walls

3.2.1 Floor above garage

DOE Zero Energy Ready Home

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 performing retrofits on existing homes are welcome to seek certification for those homes through this voluntary program.

The U.S. Department of Energy Zero Energy Ready Home National Program Requirements specify as a mandatory requirement (Exhibit 1, #2.2) that, for all labeled homes, whether prescriptive or performance path, ceiling, wall, floor, and slab insulation shall meet or exceed 2012 IECC levels. See the guide 2012 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

2009 IECC

Section 402.4 Air leakage (Mandatory).

Section 402.4.1 Building Thermal Envelope.

Section 402.4.2 Air sealing and insulation.

Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria

20122015, and 2018 IECC

Section R402.4 Air leakage (Mandatory).

Section R402.4.1 Building Thermal Envelope.

Table R402.4.1.1 Air Barrier and Insulation Installation

Retrofit: 200920122015, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 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 IRC

Section R302.5 Dwelling/garage opening/penetration protection.

Section R302.6 Dwelling/garage fire separation.

Table R302.6 Dwelling/Garage Separation.

Section R315.2 Where required in existing dwellings.

Section N1102.4 Air leakage (Mandatory).

Section N1102.4.1 Building Thermal Envelope.

Section N1102.4.2 Air sealing and insulation.

Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria

20122015, and 2018 IRC

Section R302.5 Dwelling/garage opening/penetration protection.

Section R302.6 Dwelling/garage fire separation.

Table R302.6 Dwelling/Garage Separation.

Section R315.3 Where required in existing dwellings.

Section N1102.4 Air leakage (Mandatory).

Section N1102.4.1 Building Thermal Envelope.

Table N1102.4.1.1 Air Barrier and Insulation Installation

Retrofit: 200920122015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 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

  1. Author(s): IBACOS
    Organization(s): IBACOS
    Publication Date: May, 2014

    Case study describing a stand-off furring strategy that minimizes the physical connections to each existing wall stud, uses spray foam to encapsulate existing siding materials (including lead paint), and creates a vented rain screen assembly to promote drying.

References and Resources*

  1. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: December, 2013
    Standard outlining industry procedure for sizing residential duct systems.
  2. Author(s): Air Conditioning Contractors of America
    Organization(s): Air Conditioning Contractors of America
    Publication Date: January, 2011

    Standard covering equipment sizing loads for single-family-detached homes, small multi-unit structures, condo­miniums, town houses and manufactured homes.

  3. Author(s): Rutkowski
    Organization(s): Air Conditioning Contractors of America
    Publication Date: December, 2015
    The manual covers residential zoning issues - multiple, single-zone, and central multi-zone systems - and includes advice on working with homeowners to adapt the heating or cooling system design to meet modern home design features.
  4. Author(s): ASHRAE
    Organization(s): ASHRAE
    Publication Date: December, 2013
    Standard 55 specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces.
  5. Author(s): Burdick
    Organization(s): IBACOS
    Publication Date: December, 2014
    Report outlining the issues with using existing ducts with a new low-load HVAC system, which reduces throw at supply registers causing decreased mixing of supply and room air, leading to potential thermal comfort complaints.
  6. Author(s): Herk, Poerschke
    Organization(s): IBACOS
    Publication Date: April, 2015
    The New York State Energy Research and Development Authority (NYSERDA) is interested in finding cost-effective solutions for deep energy retrofits (DERs) related to exterior wall insulation in a cold climate, with targets of 50% peak load reduction and 50% space conditioning energy savings.
  7. Author(s): Joint Center for Housing Studies of Harvard University
    Organization(s): Joint Center for Housing Studies of Harvard University
    Publication Date: June, 2010

    Even as the worst housing market correction in more than 60 years appeared to turn a corner in 2009, the fallout from sharply lower home prices and high unemployment continued.

Contributors to this Guide

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

Last Updated: 12/14/2015