Walls Behind Showers and Tubs

    Scope Images
    Image
    Install an air barrier behind showers and tubs installed on exterior walls.
    Scope

    Install an air barrier behind showers and tubs installed on exterior walls.

    • Install insulation without misalignments, compressions, gaps, or voids in all exterior wall cavities behind tubs and showers.
    • Cover the wall cavities with a rigid air barrier or other supporting material to prevent cavity insulation from sagging and to create a continuous thermal barrier.
    • Seal all seams, gaps, and holes in the air barrier with caulk or foam before tub/shower installation. Rigid air barrier materials for use behind showers and tubs include fiber-cement, fiber-reinforced gypsum, glass mat gypsum, or fiber mat-reinforced cementitious backer panels. See the guide [WM.4.2] Cement Board Installed behind Tile and Panel Tub and Shower Enclosures for more information.

    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

    When tubs and showers are installed on exterior walls, builders may forget to insulate and air seal the exterior wall behind the tub or shower surround. Neglecting to insulate and air seal here can result in significant heat loss and complaints from homeowners about tubs, showers, and bathrooms that are always cold. The insulation behind the tub or shower should be equivalent to the insulation in the rest of the exterior walls and should be covered with an air barrier of cement backer board, rigid foam insulation, or non-paper-faced drywall that is sealed at the edges and seams to provide a continuous air seal. Any type of insulation may be installed as long as it completely fills the void and will be in full contact with the air barrier. These materials may be installed by insulators, framers, or subcontractors or vendors hired specifically to install the tub or shower. This task should be included in the contract for the appropriate trade depending on the workflow at specific job sites.

    Air barrier effectiveness is measured at the whole-house level. High-performance branding programs and the IECC code require that builders meet specified infiltration rates at the whole-house level. See the “compliance” tab for these specified infiltration rates.

    How to Install a Fully Aligned Air Barrier on the Walls behind Showers and Tubs

    1. Install exterior rigid foam sheathing. Fill the entire wall cavity with insulation to the R-value required by local code or higher.
    2. Install 2x4 blocking between the wall studs, if needed, to support the air barrier.
    3. Cut cement board, fiber cement board, paperless gypsum board, Thermo-Ply, or other thin barrier material to size to cover area behind tub (see Figures 1 and 2). Apply a thick bead of caulk to the surface of exposed studs, wood blocking, and bottom plate. Nail or screw the thin-profile air barrier material to the studs. Note: moisture-resistant gypsum board or “green board” is not recommended. Cement board is not waterproof; it must be coated with a fluid-applied waterproofing, or a water-resistive barrier must be applied behind it that allows drainage (See the guide Cement Board Installed Behind Tile and Panel Tub and Shower Enclosures).
    4. Use caulk or foam to seal seams and any holes made through the air barrier material.
    5. Install the new tub.
    6. Block holes around the tub drain with sheet goods and spray foam.
    7. Finish the walls by installing fiberglass wall panels or tiling the surface.
    Draft stopping and air barrier at tub enclosure − side view.
    Figure 1. Draft stopping and air barrier at tub enclosure − side view. (Source: Building Science Corporation.)

     

    Draft stopping and air barrier at tub enclosure - plan view.
    Figure 2. Draft stopping and air barrier at tub enclosure - plan view. (Source: Building Science Corporation.)

     

    Ensuring Success

    Blower door testing conducted as part of building performance testing may help indicate whether air leakage behind a bathtub or shower has been successfully sealed. An infrared camera can be used in conjunction with the blower door testing to inspect the insulation and to detect air leakage behind the tub or shower, especially if the tub or shower is installed on an exterior wall. Insulation and air barrier installation should be inspected by the site supervisor.

    Typical R-values for common insulation materials are summarized in this table, which also identifies the vapor retarder classification for each insulation.

    Climate

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

    Rater Field Checklist

    Thermal Enclosure System.
    2. Fully-Aligned Air Barriers.6 At each insulated location below, a complete air barrier is provided that is fully aligned as follows:
    Walls: At exterior vertical surface of wall insulation in all climate zones; also at interior vertical surface of wall insulation in Climate Zones 4-8.8
    2.2 Walls behind showers, tubs, staircases, and fireplaces.

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 2 DOE Zero Energy Ready Home Target Home.
    The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements (Rev 07), as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.

    Exhibit 2, Insulation and Infiltration) Whole house leakage must be tested and meet the following infiltration limits:

    • Zones 1-2: ≤ 3 ACH50;
    • Zones 3-4: ≤ 2.5 ACH50;
    • Zones 5-7: ≤ 2 ACH50;
    • Zone 8: ≤ 1.5 ACH50;
    • Attached dwellings: ≤ 3 ACH50.

    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, 2012, 2015, and 2018 (Source: International Code Council).

     

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

     

    Right and Wrong Images
    Image
    Wrong – Insulation has compression and misalignment
    Wrong – Insulation has compression and misalignment
    Image
    Right – Insulation meets RESNET Grade I prior to air barrier installation
    Right – Insulation meets RESNET Grade I prior to air barrier installation
    Image
    Wrong – No air barrier installed prior to tub installation
    Wrong – No air barrier installed prior to tub installation
    Image
    Right – Air barrier installed behind shower stall
    Right – Air barrier installed behind shower stall
    Image
    Wrong – No air barrier installed prior to tub installation
    Wrong – No air barrier installed prior to tub installation
    Image
    Right – Air barrier installed behind the tub
    Right – Air barrier installed behind the tub
    Image
    Wrong – Air barrier not sealed
    Wrong – Air barrier not sealed
    Image
    Right – Air barrier sealed
    Right – Air barrier sealed
    Image
    Wrong – Air barrier missing behind tub area
    Wrong – Air barrier missing behind tub area
    Image
    Wrong – Air barrier missing behind tub area
    Wrong – Air barrier missing behind tub area
    Image
    Wrong – Air barrier missing behind tub area
    Wrong – Air barrier missing behind tub area
    Image
    Right – Blocking was installed in the walls behind the tub for installation of grab bars.
    Right – Blocking was installed in the walls behind the tub for installation of grab bars.
    Image
    Right – The air- and water-barrier material lining the shower stall is mastic sealed to prevent leakage and rigid foam insulation is installed on the floor of the shower.
    Right – The air- and water-barrier material lining the shower stall is mastic sealed to prevent leakage and rigid foam insulation is installed on the floor of the shower.
    Videos
    CAD
    CAD Files
    Air sealing behind tub with thin-profile sheathing - section
    Air sealing behind tub with thin-profile sheathing - section
    Download: DWG PDF
    Air sealing behind shower with thin-profile sheathing
    Air sealing behind shower with thin-profile sheathing
    Download: DWG PDF
    Air sealing behind tub with cavity rigid insulation
    Air sealing behind tub with cavity rigid insulation
    Download: DWG PDF
    Air sealing behind shower with cavity rigid insulation
    Air sealing behind shower with cavity rigid insulation
    Download: DWG PDF
    Air sealing at corner vertical bathtub chase
    Air sealing at corner vertical bathtub chase
    Download: DWG PDF
    Air sealing at corner vertical chase
    Air sealing at corner vertical chase
    Download: DWG PDF

    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)

    Rater Field Checklist

    Thermal Enclosure System.
    2. Fully-Aligned Air Barriers.6 At each insulated location below, a complete air barrier is provided that is fully aligned as follows:
    Walls: At exterior vertical surface of wall insulation in all climate zones; also at interior vertical surface of wall insulation in Climate Zones 4-8.8
    2.2 Walls behind showers, tubs, staircases, and fireplaces.

    Footnote 6) For purposes of this Checklist, an air barrier is defined as any durable solid material that blocks air flow between conditioned space and unconditioned space, including necessary sealing to block excessive air flow at edges and seams and adequate support to resist positive and negative pressures without displacement or damage. EPA recommends, but does not require, rigid air barriers. Open-cell or closed-cell foam shall have a finished thickness ≥ 5.5 in. or 1.5 in., respectively, to qualify as an air barrier unless the manufacturer indicates otherwise. If flexible air barriers such as house wrap are used, they shall be fully sealed at all seams and edges and supported using fasteners with caps or heads ≥ 1 in. diameter unless otherwise indicated by the manufacturer. Flexible air barriers shall not be made of kraft paper, paperbased products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.

    Footnote 8) All insulated vertical surfaces are considered walls (e.g., above and below grade exterior walls, knee walls) and must meet the air barrier requirements for walls. The following exceptions apply: air barriers recommended, but not required, in adiabatic walls in multifamily dwellings; and, in Climate Zones 4 through 8, an air barrier at the interior vertical surface of insulation is recommended but not required in basement walls or crawlspace walls. For the purpose of these exceptions, a basement or crawlspace is a space for which ≥ 40% of the total gross wall area is below-grade.

    Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    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. See the guide 2015 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

    Exhibit 2 DOE Zero Energy Ready Home Target Home.
    The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements (Rev 07), as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.

    Exhibit 2, Insulation and Infiltration) Insulation levels shall meet the 2015 IECC and achieve Grade 1 installation, per RESNET standards. Whole house leakage must be tested and meet the following infiltration limits:

    • Zones 1-2: ≤ 3 ACH50;
    • Zones 3-4: ≤ 2.5 ACH50;
    • Zones 5-7: ≤ 2 ACH50;
    • Zone 8: ≤ 1.5 ACH50;
    • Attached dwellings: ≤ 3 ACH50.

    Footnote 12) Building envelope assemblies, including exterior walls and unvented attic assemblies (where used), shall comply with the relevant vapor retarder provisions of the 2015 International Residential Code (IRC).
    Footnote 23) Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.

     

    2009 International Energy Conservation Code (IECC)

    Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Air Barrier and Insulation Installation, Shower/tub on exterior wall: Exterior walls adjacent to showers and tubs are insulated and have air barrier separating the wall from the shower and tubs. Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.

    2012 IECC

    Table R402.4.1.1 Air Barrier and Insulation Installation, Shower/tub on exterior wall: Exterior walls adjacent to showers and tubs are insulated and have air barrier separating the wall from the shower and tubs. Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.

    20152018, and 2021 IECC

    Table R402.4.1.1 Air Barrier and Insulation Installation. Shower/tub on exterior wall: Exterior walls adjacent to showers and tubs are insulated and have air barrier separating the wall from the shower and tubs. General requirements: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air-permeable insulation is not used as a sealing material.

    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 International Residential Code (IRC)

    Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria, Shower/tub on exterior wall: Insulation exists between showers/tubs and exterior wall. Air barrier and sealing exists on common walls between dwelling units, on exterior walls behind tubs/showers, and in openings between window/door jambs and framing. Table N1102.4.2, Air barrier and thermal barrier: Exterior wall insulation is installed in substantial contact and continuous alignment with the air barrier. Air permeable insulation is not used as a sealing material.

    2012 IRC

    Table N1102.4.1.1 Air Barrier and Insulation Installation, Shower/tub on exterior wall: Exterior walls adjacent to showers and tubs are insulated and have an air barrier separating the wall from the shower and tubs. Table N1102.4.1.1, Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.

    20152018, and 2021 IRC

    Table N1102.4.1.1 Air Barrier and Insulation Installation, Shower/tub on exterior wall: Exterior walls adjacent to showers and tubs are insulated and have air barrier separating the wall from the shower and tubs. General requirements: A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.

    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.

     

    American Society for Testing Materials (ASTM) E1677-11

    Standard Specification for Air Barrier (AB) Material or System for Low-Rise Framed Building Walls. This specification covers minimum performances and specification criteria for an air barrier material or system for framed, opaque walls of low-rise buildings. The provisions are intended to allow the user to design the wall performance criteria and increase air barrier specifications for a particular climate location, function, or design.

     

    Air Barrier Association of America (ABAA) 07261

    Self-Adhered Sheet Air Barrier. 2006. Air Barrier Association of America, Walpole, MA. This specification for self-adhered sheet air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

    ABAA 07262

    Fluid-Applied Air and Vapor Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for air barriers that are fluid-applied and also act as vapor barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

    ABAA 07263

    Closed Cell, Medium-Density Spray Polyurethane Foam Air Barrier. 2011. Air Barrier Association of America, Walpole, MA. This specification for closed-cell, medium-density spray polyurethane foam air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

    ABAA 07265

    Fluid-Applied Vapor Permeable Air Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for fluid-applied vapor permeable air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

    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.

    References and Resources*
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.
    *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 Measures
    Building Science-to-Sales Translator

    Fully Aligned Air Barriers = Whole-House Draft Barrier

    Image(s)
    Technical Description

    A whole-house draft barrier is a continuous layer of air-tight materials that block air leaks. This barrier can be integrated with other materials to also function as a water barrier, thermal barrier, and vapor barrier. For example, rigid foam insulation can be used to block thermal flow as well as air flow when seams are sealed with tape, caulk, adhesives, or liquid-applied sealants. Some rigid foams have an integrated water control layer as well. Additionally, drywall can serve as an interior air barrier when the seams are taped and spackled, and caulk, spray foam, or gaskets are used to seal around wiring, plumbing, and other penetrations. It also serves as the vapor barrier when finished with paint. Insulation should be in full contact with the air barrier layer.

    Whole-House Draft Barrier
    Sales Message

    Whole-house draft barriers block air flow that can undermine the thermal protection with a complete high-performance insulation system. What this means to you is less wasted energy along with enhanced comfort, quiet, and durability. Wouldn’t you agree it would be a shame to only get a partial return on your investment in advanced insulation?

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