Walls Behind Showers and Tubs
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 cementitous backer panels. See the guide [WM.4.2] Moisture-Resistant Backing Material at Walls Behind Tubs and Showers for more information.
See the Compliance Tab for related codes and standards, and criteria to meet national programs such as ENERGY STAR Certified Homes, DOE’s Zero Energy Ready Home program, and EPA’s Indoor airPLUS.
When tubs and showers are installed on exterior walls, builders sometimes 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
- Install exterior rigid foam sheathing. Fill the entire wall cavity with insulation to the R-value required by local code or higher.
- Install 2x4 blocking between the wall studs, if needed, to support the air barrier.
- Cut cement board, fiber cement board, paperless gypsum board, Thermo-Ply, or other thin barrier material to size to cover area behind tub. 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.
- Use caulk or foam to seal seams and any holes made through the air barrier material.
- Install the new tub.
- Block holes around the tub drain with sheet goods and spray foam.
- Finish the walls by installing fiberglass wall panels or tiling the surface.
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, if the tub or shower is installed on an exterior wall and if a sufficient temperature difference exists between the outside and the conditioned space of the house. Insulation and air barrier installation should be inspected by the site supervisor before the tub or shower is installed.
ENERGY STAR Certified Homes
[Note: Guidance for ENERGY STAR Certified Homes Version 3.0, Revision 08 is coming soon.]
ENERGY STAR Certified Homes (Version 3.0, Revision 07), Thermal Enclosure Checklist, Fully-Aligned Air Barriers. A complete air barrier that is fully aligned with insulation is to be provided at exterior surface of walls in all climate zones and at interior surface of walls for Climate Zones 4-8.
DOE Zero Energy Ready Home
Exhibit 2: DOE Zero Energy Ready Home Target Home. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.
ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), Rater Field Checklist
Thermal Enclosure System:
2. Fully-Aligned Air Barriers.5 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 4-8.7
2.2 Walls behind showers, tubs, staircases, and fireplaces.
(5) 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, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.
(7) 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.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
Exhibit 2: DOE Zero Energy Ready Home Target Home. Certified under ENERGY STAR Qualified Homes Version 3. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol. Building envelope assemblies, including exterior walls and unvented attic assemblies (where used), shall comply with the relevant vapor retarder provisions of the 2012 International Residential Code.
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.
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.
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.
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.
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.
Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Fireplace: Walls with fireplaces include air barriers.* Table 402.4.2, 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.*
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.*
Table R402.4.1.1 Air Barrier and Insulation Installation, Fireplace: Fireplace walls have air barrier and closure doors are gasketed.* Table R402.4.1.1, 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.*
Table N1220.127.116.11 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.* Table N118.104.22.168, 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.*
*Due to copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.
Fully Aligned Air Barriers = Whole-House Draft Barrier