Air Sealing Multifamily Party Walls

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Scope

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.

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 Reference

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 Reference

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 Reference

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.

Training

Right and Wrong Images

Presentations

None Available

Videos

None Available

CAD Images

Compliance

ENERGY STAR Certified Homes

ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), 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.

ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.

DOE Zero Energy Ready Home

Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3

2009 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.* 

2009 IRC

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

2012 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.*

2012 IRC

Table N11402.4.1.1 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.*

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

2015 IECC

2015 IRC

More Info.

Contributors to this Guide

The following Building America Teams 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

 

Case Studies

None Available

References and Resources*

  1. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: May, 2009

    Brochure about creating an air barrier by sealing drywall assemblies.

  2. Author(s): Baechler, Gilbride, Hefty, Cole, Williamson, Love
    Organization(s): PNNL, ORNL
    Publication Date: April, 2010

    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.

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

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

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

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

  5. Author(s): Otis, Maxwell
    Organization(s): CARB, NREL
    Publication Date: June, 2012

    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.

  6. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: May, 2009

    Information sheet about air sealing.

  7. 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

Tight Air Sealed Home =
Comprehensive Draft Protection

Technical Description: 

Poorly air-sealed homes are less comfortable and cost more to maintain because they introduce drafts, cold spots, moisture, and insects into the home. Builders can provide a home with comprehensive draft protection by installing a continuous air barrier around the whole house and by taking extra care to caulk and seal in all those places where holes and cracks may be lurking - 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. Some builders use spray foam insulation in the walls, rim joists, and/or attic to insulate and air seal at the same time.

Alternate Terms

Air Contaminant Sealing
Comprehensive Energy Seal
Advanced Home Sealing Technology
Moisture Sealed Construction
Comprehensive Draft Protection
Sales Message
Comprehensive draft protection blocks 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, 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?
Last Updated: 03/14/2016

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