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

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

    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 nail each piece in place, then seal edges with caulk or fire-blocking 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 fire-blocking 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 (Source: Measure Guideline: Air Sealing Attics in Multifamily Buildings 2012). 

     

    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 (Source: Measure Guideline: Air Sealing Attics in Multifamily Buildings 2012). 

     

    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 fire-stopping 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 (Source: Measure Guideline: Air Sealing Attics in Multifamily Buildings 2012). 

     

    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 (Source: Measure Guideline: Air Sealing Attics in Multifamily Buildings 2012). 

     

    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.
    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 (Source: Measure Guideline: Air Sealing Attics in Multifamily Buildings 2012). 

     

    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

    Colder climates will increase the potential for heat loss and air leakage, and the impacts of that heat loss, if the top plates are not properly insulated and air sealed.  Heat loss into the attic can warm the underside of the roof deck which can contribute to snow melt and ice dam formation. Significant air leakage from the house into the attic increases the potential for condensation and frost formation in the attic, if warmer vapor-laden conditioned air is allowed to escape into a wintertime attic with cold surfaces.

    Right and Wrong Images
    Image
    Right – Continuous top plate installed
    Right – Continuous top plate installed
    Image
    Right – Continuous top plate installed
    Right – Continuous top plate installed
    Image
    Wrong – Wall from above without top plate or blocking installed
    Wrong – Wall from above without top plate or blocking installed
    Image
    Right – Blocking installed and air sealed instead of continuous top plate
    Right – Blocking installed and air sealed instead of continuous top plate
    Image
    Wrong – Top plate not air sealed
    Wrong – Top plate not air sealed
    Image
    Wrong – Top plate not air sealed
    Wrong – Top plate not air sealed
    Image
    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.
    Image
    Right – The top plate-to-dry wall seams of the interior walls are sealed from the attic.
    Right – The top plate-to-dry wall seams of the interior walls are sealed from the attic.
    Image
    Right – A bead of sealant will form an airtight gasket between the top plate and drywall.
    Right – A bead of sealant will form an airtight gasket between the top plate and drywall.
    Image
    Right – All electrical box are carefully sealed as are all top plate-to-drywall seams.
    Right – All electrical box are carefully sealed as are all top plate-to-drywall seams.
    Videos
    CAD
    CAD Files
    Conceptual air sealing strategy - upper wall section
    Conceptual air sealing strategy - upper wall section
    Download: DWG PDF
    Conceptual line of continuous air barrier - upper wall section
    Conceptual line of continuous air barrier - upper wall section
    Download: DWG PDF
    Air seal at duct boot
    Air seal at duct boot
    Download: DWG PDF
    Air seal at top plate pipe penetration
    Air seal at top plate pipe penetration
    Download: DWG PDF
    Air seal at top plate electrical penetration
    Air seal at top plate electrical penetration
    Download: DWG PDF
    Air seal at chase walls - plan
    Air seal at chase walls - plan
    Download: DWG PDF

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

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

    2012, 2018, and 2021 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, 2018,  and 2021 IECC

    Section R101.4.3 (in 2009 and 2012). 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.)

    Chapter 5 (in 2015, 2018, 2021). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.

     

    20092012, 2015, 2018, and 2021 International Residential Code (IRC)

    Table N1102.4.1.1 (N1102.4.2 in 2009 IRC) 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 IRC

    Section R102.7.1 Additions, alterations, or repairs. 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 the requirements of this code, unless otherwise stated. (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.

    Existing Homes

    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.

    • global worker safety.
    • worker health and safety specifications related to air sealing.
    • general air sealing of attics.
    • insulating attic ceilings.
    • soffit ventilation and baffles.
    • combustion safety, which may be impacted by air sealing.

    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 (2014) 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.
    Figure 1. 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 (Source: 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
    Figure 2. The missing top plate in a kneewall was covered with lumber and rigid foam insulation and then sealed with spray foam (Source: 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 guide 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.

    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)
    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)
    Lstiburek
    Organization(s)
    Building Science Corporation
    Publication Date
    Description
    Report that provides information and specifications to anyone that is attempting to air seal existing attics.
    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.
    *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.

    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

    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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