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Air Seal Top Plates or Blocking Missing at Top of Walls Adjoining Unconditioned Spaces

Scope

Install continuous top plates or blocking at the tops of walls adjacent to conditioned space to minimize air leakage.
Install continuous top plates or blocking at the tops of walls adjacent to conditioned space to minimize air leakage.

Install continuous top plates or blocking at the tops of walls adjacent to unconditioned space to minimize air leakage. 

  • Design walls with top plates. Do not specify balloon framing.
  • Install a continuous top plate at all full height walls.
  • Where walls of varying heights meet, install blocking if needed in any wall cavities that are open to an unconditioned attic or other unconditioned space. Use rigid blocking material such as lumber, plywood, OSB, or rigid foam, caulked or sealed at edges.

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

Most wall cavities are composed of a horizontal top plate, a horizontal bottom plate, and the vertical studs. When gypsum board and wall sheathing are caulked and fastened to the inside and exterior faces of these components, they create an air-tight six-sided wall cavity. If one element is missing from this assembly or is not adequately air sealed to the other elements, air will flow through the cavity, potentially robbing any insulation present of its insulating value. Some wall designs have no top plate so the wall cavity is open to the area above, which may be an unconditioned attic or other unconditioned space. This opening can become a pathway allowing unconditioned air from the attic to flow down into the wall cavity and conditioned air from the wall to flow up into the attic. The result is unwanted heat loss or heat gain, cold spots in walls, and an increased potential for moisture problems in the wall or attic.

Missing top plates can sometimes occur when a room of one ceiling height abuts a room of a taller ceiling height. They can also occur when buildings are designed with balloon framing. Designers should not specify balloon framing. If the house design includes varying ceiling heights, blocking should be specified where the top of the lower wall meets the side of the higher wall if no top plate is present. This blocking material could be rigid foam, plywood, OSB, or lumber that is cut to fit. Alternately, the open stud cavities can be filled with fiberglass batting that is rolled and tucked into the cavity opening then covered with spray foam.

How to Air Seal a Wall with a Missing Top Plate

  1. Identify missing top plates in adjoining walls with different ceiling heights.
  2. Select a rigid air-blocking material (rigid foam insulation, plywood, OSB, lumber). Cut into pieces to fit each stud bay. Wrap a thin piece of strapping around the board to hold it in position while you glue each end with caulk or spray foam. Pull the strap out and glue the remaining two sides.
  3. Or, roll a piece of unfaced fiberglass batt insulation for each cavity. Pressure fit the fiberglass batt roll into the top of the stud cavity. Cover the top with spray foam to air seal the roll and hold it in place. 
The top plate is missing where the lower wall meets the upper wall
Figure 1 - Ceiling heights may vary within a house design, for example, the ceiling in a hallway or bathroom may be lower than the ceiling in an adjoining dining room or bedroom. Where a lower ceiling meets the wall of a room with a higher ceiling, the lower wall may be missing a top plate, creating an open air pathway from the stud cavities to the attic space.

 

Fill in the hole left by the missing top plate with a rigid air blocking material or rolled batt insulation that is spray foamed in place
Figure 2 - Top plates may be missing where a lower ceiling meets the wall of a room with a higher ceiling. The open wall cavities should be closed off with an air-blocking material like rigid foam, plywood, or dimensional lumber that is cut to fit the stud cavity and sealed in place with caulk or spray foam or fiberglass batt insulation that is rolled and friction fit into place and air sealed with spray foam.

 

How to Air Seal Open Wall Cavities in Balloon-Framed Walls

  1. Identify open wall cavities in balloon-framed walls. Note, balloon framed walls are walls that have no top plates so wall cavities are open from the bottom plate to the attic. This style of construction is not recommended.
  2. Roll a piece of fiberglass batt and stuff it into place at the top of the wall where the top plate is missing.
  3. Cover the roll of fiberglass batt with spray foam to air seal it in place.
  4. Fill the attic with additional insulation.
Balloon framing at a gable end wall allows air to flow from the attic down into the wall cavity
Figure 3 - Balloon framing at a gable end wall allows air to flow from the attic down into the wall cavity

 

Roll a piece of fiberglass batt and stuff it into place at the top of the wall
Figure 4 - The space at the top of the wall can be filled with a piece of fiberglass batt that is rolled up and stuffed in place

 

Cover the roll of fiberglass batt with spray foam to airseal it in place
 Figure 5 - The fiberglass roll is covered with spray foam to air seal the top of the wall. The top plate of the wall under the rafter can also be spray foamed between the ceiling gypsum and the bottom side of the rafter insulation baffle. Then the area can be covered with blown insulation.  

 

Ensuring Success

Design homes so that all full-height walls have a continuous top plate. If the house plan has some area where a top plate cannot practically be included in the framing design, such as where a room with a lower ceiling height abuts a room with a higher ceiling height, indicate on the plans that air-blocking material should be installed, then inspect that it is properly installed and sealed in place with caulk or spray foam.

Climate

No climate specific information applies.

Training

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Presentations

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Videos

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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

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):

4.4 Continuous top plate or blocking is at top of walls adjoining unconditioned space, and sealed. 

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, Walls: Corners, headers, narrow framing cavities, and rim joists are insulated.

2012, 2015, and 2018 IECC

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, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 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 IRC

Table N1102.4.2 Air Barrier and Insulation Inspection, Walls: Corners, headers, narrow framing cavities, and rim joists are insulated.

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, 2015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 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.

This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.

SCOPE

See the techniques described in the Description tab of this guide, which apply well to existing homes.

  • Use precautions when accessing attics, as described below.
  • If this work is part of an effort to insulate an attic, consider this and other attic air-sealing measures before installing the insulation.  

The U.S. Department of Energy’s Standard Work Specifications (SWS) define minimum requirements to ensure that the work performed during home energy upgrades is effective, durable, and safe. The Standard Work Specifications include specifications for the following topics, which may be applicable to air sealing walls at missing top plates.

DESCRIPTION

The techniques described for air sealing at missing top plates in the new home tabs for this guide apply well to existing homes.

It may be difficult to access the top plates or the areas where top plates should be. These attic areas may be most accessible when other projects are underway, such as when roofing is being installed, when insulation is being installed (reroofing is also a good time to add insulation), or when a wall is being repaired.

Some attic areas, such as over porches or in isolated sections of the attic, may not have access panels or doors. If comfort or energy bills are being impacted, then adding an access panel may be justified; however, steps must be taken to control dust when cutting through existing walls or ceilings in homes built before 1978, which may contain lead paint. Old plaster may contain asbestos. See the assessment guide on hazardous materials and the EPA Healthy Indoor Environment Protocols for Home Energy Upgrades (2011) for more information.

This kneewall has no top plate and the resulting gap provides a wide-open pathway for air and vapor to travel between the living space and the attic, even though the cavity has been filled with insulation
This kneewall has no top plate and the resulting gap provides a wide-open pathway for air and vapor to travel between the living space and the attic, even though the cavity has been filled with insulation. Image courtesy of Energy Smart Academy.

The missing top plate in a kneewall was covered with lumber and rigid foam insulation and then sealed with spray foam
The missing top plate in a kneewall was covered with lumber and rigid foam insulation and then sealed with spray foam. Image courtesy of Energy Smart Academy.

To minimize crumbling of plaster when cutting through existing plaster and wood lathe surfaces, use high-speed cutting tools such as powered multi-tools or an angle grinder with a diamond blade, to make clean cuts through the plaster and lathe. Protect surfaces, hang tarps to isolate the area, and operate a shop vac to capture the dust. Another trick is to apply a sealing compound to the back side of the lathe, if it is accessible, prior to cutting to minimize flexing. Apply masking tape to the lines to be cut to help hold the plaster together. Wetting may also help reduce dust generation.

If this work is being undertaken as part of a project to insulate the attic, consider other attic air-sealing activities before insulation is installed. (See the Attic Air Sealing Guide and Details). Air sealing should be done before insulation is installed. Once in the attic space, look for duct work that needs air sealing and insulation. (There are many guides on this topic in the Solution Center).

To avoid durability issues and hazardous conditions, use the pre-retrofit assessment guides for attics  and walls.

The approaches used for air sealing may depend on whether the unconditioned space will be ventilated or treated as a conditioned space. See the guides on insulating existing attics or roofs in the Existing Homes tool.

Air sealing may impact the amount of air available for combustion appliances. If combustion appliances are present in the home, before starting the air sealing, see the Pre-Retrofit Assessment of Combustion Appliances for ways to ensure that there is adequate fresh air for combustion appliances. In ventilated attics, ensure there is adequate ventilation as described in the guide on Calculating Attic Passive Ventilation.

COMPLIANCE

See Compliance tab. 

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.

Case Studies

None Available

References and Resources*

  1. Author(s): Baechler, Gilbride, Hefty, Cole, Williamson, Love
    Organization(s): Pacific Northwest National Laboratory, Oak Ridge National Laboratory
    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.

  2. Author(s): Department of Energy
    Organization(s): DOE
    Publication Date: April, 2017

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

  3. Author(s): U.S. Environmental Protection Agency
    Organization(s): EPA
    Publication Date: December, 2015

    Webpage with links to Document outlining the program requirements for ENERGY STAR Certified Homes, Version 3 and 3.1  (Rev. 08).

  4. Author(s): Lstiburek
    Organization(s): Building Science Corporation
    Publication Date: January, 2010

    Fact sheet providing detailed information about air sealing attics.

  5. Author(s): Otis, Maxwell
    Organization(s): CARB, National Renewable Energy Laboratory, Steven Winter Associates, SWA
    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): Building Science Corporation
    Publication Date: September, 2014

    Report that provides information and specifications to anyone that is attempting to air seal existing attics.

  7. Author(s): U.S. Environmental Protection Agency
    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.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

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

Building Science Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team

Last Updated: 02/13/2018