Walls Behind Showers and Tubs

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Scope

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

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 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 Reference

 

Draft stopping and air barrier at tub enclosure - plan view

 

Figure 2 - Draft stopping and air barrier at tub enclosure − plan viewReference

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.

Climate

ENERGY STAR Certified Homes 
ENERGY STAR Certified Homes (Ver. 3/3.1 Ver 08) Rater Field Checklist, A complete air barrier that is fully aligned with insulation is installed at the exterior vertical surface of wall insulations in all climate zones and also at the interior vertical surface of walls in Climate Zones 4-8.
 

DOE Zero Energy Ready Home
DOE Zero Energy Ready Home (Rev 05), Exhibit 2: DOE Zero Energy Ready Home Target Home. Infiltration:  Climate Zones 1-2: 3 ACH 50; Zones 3-4: 2.5 ACH50; Zones 5-7: 2 ACH50; Zone 8: 1.5 ACH50. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.

 

climate zone map

Training

Right and Wrong Images

Presentations

None Available

Videos

  1. Walls Behind Showers and Tubs (1)
    Publication Date: July, 2015
    Courtesy Of: BMI

    Video describing how to properly insulate walls behind showers and tubs. 

  2. Walls Behind Showers and Tubs (2)
    Publication Date: July, 2015
    Courtesy Of: NYSERDA

    Video describing how to properly insulate walls behind showers and tubs.

  3. Walls Behind Showers and Tubs (3)
    Publication Date: July, 2015
    Courtesy Of: Train2Build

    Video describing how to properly insulate walls behind showers and tubs.

CAD Images

Compliance

ENERGY STAR Certified Homes

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.

Footnotes:

(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.

DOE Zero Energy Ready Home

DOE Zero Energy Ready Home (Rev 05) Exhibit 1: Mandatory Requirements: Item 1, Homes must be certified under ENERGY STAR Qualified Homes Version 3. Item 2, Ceiling, wall, floor, and slab insulation shall meet or exceed 2012 or 2015 IECC levels.

Exhibit 2: Design the home to meet the HERS index of the DOE Zero Energy Ready Home Target Home, for which insulation levels must meet the 2012 IECC and achieve Grade 1 installation, per RESNET standards.
Exhibit 2:  Infiltration: Climate Zones 1-2: 3 ACH 50; Zones 3-4: 2.5 ACH50; Zones 5-7: 2 ACH50; Zone 8: 1.5 ACH50. 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.

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.

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.

2009 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.*

2009 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 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.*

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.*

2015 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.*

2015 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.*

*Due to copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.

More Info.

Contributors to this Guide

The following Building America Teams contributed to the content in this Guide.

Case Studies

None Available

References and Resources*

  1. Author(s): DOE
    Organization(s): DOE
    Publication Date: May, 2015

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  2. Author(s): EPA
    Organization(s): EPA
    Publication Date: September, 2015

    Document outlining the program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 08).

  3. Author(s): EPA
    Organization(s): EPA
    Publication Date: October, 2011

    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.

Building Science-to-Sales Translator

Fully Aligned Air Barriers =
Whole-House Draft Barrier

Technical Description: 

A whole-house draft barrier is a continuously connected layer of solid or air-tight materials that block air leaks. This barrier can also function as part of a water barrier, thermal barrier, and vapor barrier, if the location and materials are compatible. For example, rigid foam insulation can provide a combined function. Rigid foam sheets can be used to block air flow when seams are sealed with tape, caulks or adhesives, or liquid applied sealants. An example of an interior air barrier may be the drywall on the home’s walls and ceilings, when the seams are taped and mudded, and caulk, spray foam, or gaskets are used to seal around wiring, plumbing, and other penetrations. Insulation should be in full contact with the air barrier layer.

Alternate Terms

Air Contaminant Barrier
Energy Saving Air Barrier
Advanced Air Barrier Technology
Professionally-Installed Draft Barrier
Moisture Control Air Barrier
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?
Last Updated: 03/14/2016

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