Air Sealing Multifamily Party Walls

Scope Images
Air seal the common wall between units in a multi-family structure to minimize air leakage.
Air seal the common wall between units in a multi-family structure to minimize air leakage.
Scope

Air seal the common wall between units in a multi-family structure to minimize air leakage and provide a control layer for sound, smoke, fire, and air quality.

  • In multifamily buildings, air seal the gap between the drywall shaft wall (i.e., common wall) and the structural framing between units at all exterior boundaries.
  • Confirm with local code officials which air sealing materials are is preferred for fire safety reasons. 
  • Possible air sealing materials include fireproof spray foam for sealing the bottom plate to subfloor and bottom and top plates to sheathing in wood-framed walls, fire-rated caulk around plumbing and wiring, and two-part urethane foam for masonry block walls.

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

Common walls (also called party walls) between units in multifamily housing (e.g., townhouses, duplexes, and apartments) should be constructed as airtight assemblies for sound, smoke, fire, and air quality control. However, experience has shown that these common walls can often be significant sources of air and heat loss if gaps or cracks exist in the connections between each unit’s walls.

To reduce air leakage, common wall assemblies should be air sealed at all boundaries. Wood-framed walls are sealed with fireproof spray foam. Masonry block party walls, which form “chimneys” because of their open cores, can be air sealed with two-component urethane foam, which also reduces sound and odor transfer, and dust, insect, and moisture entry. These walls are fire-rated assemblies for each unit. Acceptable materials for air sealing common walls can vary significantly around the country. Confirm with local code officials which material is preferred for fire safety reasons. Any plumbing and wiring penetrations through the drywall surfaces of the common walls should be sealed with fire-rated sealant materials (BSC 2009). The 2009 IECC requires that air barriers be installed in common walls; for more information, see the Compliance tab in this resource guide (Otis and Maxwell 2012).

Air sealing of common walls might be done by the framer. This task should be included in the contract for the appropriate trade depending on the workflow at the specific job site.

Gaps at shared common walls can be a significant source of air leakage in multi-family buildings
Figure 1 - Air gaps are sometimes left unsealed on each side of the common partition wall as shown here.

 

Use caulk, foam, or equivalent material to seal gap between common wall
Figure 2 - Spray foam can be used to seal the gaps around the top plates of common walls.

How to Air Seal a Common Wall

  1. Check local code requirements to determine appropriate fire-rated materials for air sealing common walls between dwelling units. Such materials include intumescent caulks, fire-rated (high-temperature) caulks, and fire-rated one-component foam (Otis and Maxwell 2012).

  2. Use caulk, foam or equivalent material to seal the drywall to the top plates and bottom plates of the common walls. Also seal at the seam between the top and bottom plates and the exterior sheathing.

  3. Caulk the first stud of each partition wall to the exterior wall studs.

Use caulk, foam or equivalent material to seal gap between partition wall
Figure 3 - The partitions walls are caulked to the exterior wall. A continuous piece of sheathing is run across the property line or if there is a seam in the sheathing at the dividing line it is sealed with elastomeric caulk or mastic paste.

 

Ensuring Success

Common walls (also called party walls or shared partition walls) between units in multi-family buildings should be visually checked to ensure that the gap between the drywall and the structural framing is sealed with caulk, foam or other sealing material.  Air barrier effectiveness is measured at the whole-house level. Blower door testing, which is conducted as part of the whole-house energy performance test, may help indicate whether common walls have been successfully sealed.

Climate

No climate specific information applies.

Presentations
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)

National Rater Field Checklist

Thermal Enclosure System.
4. Air Sealing (Unless otherwise noted below, “sealed” indicates the use of caulk, foam, or equivalent material). 
4.8 In multifamily buildings, the gap between the common wall (e.g. the drywall shaft wall) and the structural framing between units sealed at all exterior boundaries.

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.

2009 International Energy Conservation Code (IECC)

Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Common wall: Air barrier and sealing exists on common walls between dwelling units.

2012, 2015, and 2018 IECC

The 2012 IECC does not specifically address sealing multifamily party walls. Table R402.4.1.1 Air Barrier and Insulation Installation, Walls: Junction of foundation and wall sill plates, wall top plate and top of wall, sill plate and rim-band, and rim band and subfloor are sealed. Corners, headers, and rim joists making up the thermal envelope are insulated.

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)

Table N1102.4.2 Air Barrier and Insulation Inspection, Common wall: Air barrier and sealing exists on common walls between dwelling units.

2012, 2015, and 2018 IRC

Table N1102.4.1.1 Air Barrier and Insulation Installation, Walls: Junction of foundation and wall sill plates, wall top plate and top of wall, sill plate and rim-band, and rim band and subfloor are sealed. Corners, headers, and rim joists making up the thermal envelope are insulated.

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.

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.
Author(s)
Baechler,
Gilbride,
Hefty,
Cole,
Williamson,
Love
Organization(s)
Pacific Northwest National Laboratory,
Oak Ridge National Laboratory
Publication Date
Description
Report identifying the steps to take, with the help of a qualified home performance contractor, to seal unwanted air leaks while ensuring healthy levels of ventilation and avoiding sources of indoor air pollution.
Author(s)
Lstiburek
Organization(s)
Building Science Corporation
Publication Date
Description
Brochure about creating an air barrier by sealing drywall assemblies.
Author(s)
Lstiburek
Organization(s)
Building Science Corporation
Publication Date
Description
Information sheet about air sealing.
Author(s)
Otis,
Maxwell
Organization(s)
CARB,
National Renewable Energy Laboratory,
Steven Winter Associates,
SWA
Publication Date
Description
Document providing an understanding of the importance of the different types of multifamily building attics and their unique challenges, and outlines strategies and materials used in air sealing them.
Author(s)
U.S. Environmental Protection Agency
Organization(s)
EPA
Publication Date
Description
Website providing the technical specifications and related documents for home builders, subcontractors, architects, and other housing professionals interested in certifying a home to the EPA's Indoor airPLUS program requirements.
*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.

Pacific Northwest National Laboratory

Steven Winter Associates, lead for the Consortium for Advanced Residential Buildings (CARB), a DOE Building America Research Team

 

Building Science Measures
Building Science-to-Sales Translator

Tight Air Sealed Home = Comprehensive Draft Protection

Image(s)
Technical Description

Poorly air-sealed homes are less comfortable and cost more to maintain because they provide a pathway for drafts, cold spots, moisture, and insects into the home. Comprehensive draft protection includes a continuous air barrier around the whole house along with caulking and sealing in all holes and cracks. This includes around wiring, plumbing, ducts, and flues; where wall framing meets flooring; around windows; where drywall meets top plates and sill plates; where rim joists meet foundation walls and subfloors; etc. Spray foam insulation can be used at rim joists, floors above unconditioned space, and in attics to insulate and air seal at the same time.

Comprehensive Draft Protection
Sales Message

Comprehensive draft protection minimizes air flow that can undermine a complete high-performance insulation system. What this means for you is less wasted energy along with enhanced comfort, health, 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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