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Air Sealing Sill Plates

    Scope
    Scope Images
    Image
    Air seal above-grade sill plates adjacent to conditioned space to minimize air leakage.
    Scope

    Air seal above-grade sill plates adjacent to conditioned space to minimize air leakage.

    • Air seal between the sill plate and the sub-floor with caulk, foam, or an equivalent material. 
    • Install a foam gasket beneath sill plates that are sitting on concrete or masonry and adjacent to conditioned space to both air seal and serve as a capillary break between the concrete and the sill plate.

    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 and ENERGY STAR Single-Family New Homes.

    Description
    Description

    For a home to perform efficiently, the walls, ceiling, and foundation that comprise the building shell must provide a continuous air barrier. Any seams where two different building components come together in the building shell represent a potential source of air leakage that must be air sealed with an appropriate sealing material. The sill plate where the wall meets the concrete foundation is especially susceptible to air leakage for two reasons. First, because the concrete surface is sometimes rough, a smooth seam between the foundation and the sill plate is difficult to achieve. Additionally, the stack effect naturally pulls air in through the lower part of the building where the sill plate is located.

    The sill plate (sometimes called the mud sill) is the board laid directly on top of the foundation wall (Figure 1). It usually consists of one layer of 2x6 or 2x8 pressure-treated lumber. In platform construction, the band joist and floor joists rest on top of the sill plate. They support the subfloor and the base plate (also known as a bottom plate or sole plate), which sits on the subfloor and to which the wall studs are attached. The sill plate is attached to the foundation wall with anchor bolts that are embedded in the concrete of the foundation wall. 

      Install a sill gasket between the sill plate and the foundation wall.
      Figure 1. The sill plate-foundation wall juncture is sealed with a pliable closed-cell foam sill sealer (Source: Air Barriers - Airtight Drywall Approach, Info 401). 

      The best way to air seal the sill plate is to place a sill sealer (also called a sill gasket) on the concrete before laying down the sill plate. Sill sealer is a pliable foam product that is available in varying widths up to 10 inches wide. It comes in rolls and is rolled out over the concrete along the foundation perimeter. The flexible sill sealer product conforms to any irregularities in the surface of the concrete. A waterproof closed-cell foam product should be selected that will both air seal and provide a capillary break preventing any moisture that migrates up through the concrete from reaching the wood of the sill plate.  The rot-resistant product also prevents insect and rodent intrusion. Some builders seal the sill plate to the foundation wall with two large beads of caulk but a sill seal product that covers the whole sill plate area is preferable because of its waterproofing capability and inherent uniformity.

      The seam between the sill plate and the rim joist above is sealed with caulk (Figure 2). The entire sill plate-rim joist area can be further air sealed and insulated with spray foam, but sill plate joints and seams with rim joists should first be caulked. The hole where the anchor bolt protrudes through the sill plate can also be caulked.

        Seal the sill plate to the rim joist with caulk.
        Figure 2. The top of the sill plate is sealed to the rim joist with a bead of caulk. All joints in the sill plate are sealed with caulk (Source: Air Barriers - Airtight Drywall Approach, Info 401). 

        Sill sealer installation could 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.

        How to Air Seal the Sill Plate

        1. Lay the sill plate boards along the perimeter of the foundation. The edge of the sill plate should be set back from the outside face of the foundation a distance equal to the thickness of the exterior sheathing. Mark the locations of the anchor bolts and drill holes for the bolts. Lay the boards on the sill to ensure they fit then set them aside (Koel 2008).
        2. Install a termite shield if necessary. The termite shield is a strip of 26-gauge aluminum, copper, or galvanized sheet metal laid along the outer edge of the foundation wall. The outer edge extends out from the exterior wall and is bent down at an angle to form a drip edge and a diverter, which makes termite presence more visible (Figure 3). The shield is sealed to the concrete with epoxy and joints in the flashing are glued with epoxy or are soldered (BSC 2009b). 
        3. Roll out sill sealer along the perimeter of the foundation wall. Press down, and cut if needed to allow anchor bolts to come through the sealer. Apply caulk around anchor bolts.
        4. Lay sill board back in place over termite shield, sill sealer, and anchor bolts. Secure anchor bolts with washers and nuts.
        5. Install rim joists. Caulk at rim joist-sill plate seams (BSC 2009c).
        6. Optionally, for additional air sealing and insulation, apply spray foam to the subfloor-rim joist-sill plate juncture (Figure 4).
        A termite shield and a sill gasket are installed between the sill plate and the foundation on a raised slab foundation.
        Figure 3. A sill sealer and termite shield are installed between the sill plate and the foundation on a raised slab foundation (Source: Best Practices Series Volume 16: 40% Whole-House Energy Savings in the Mixed-Humid Climate 2011). 

         

        Spray foam provides a critical seal between the subfloor, rim joist, and sill plate.
        Figure 4. Spray foam provides a critical seal that further air seals and insulates the subfloor-rim joist-sill plate juncture (Source: Best Practices Series Volume 16: 40% Whole-House Energy Savings in the Mixed-Humid Climate 2011). 

         

        Success
        Ensuring Success

        Before drywall is installed, visually inspect that a foam gasket has been installed under the sill plate and that the sill plate is caulked to the rim joist.

        Climate
        Climate

        Pests

        Air sealing sill plates at exterior walls will minimize the entry of insects and rodents into the home.

        Termites are prevalent in the central and southern United States (see Termite Infestation Map). Corrosion-resistant stainless steel termite shields should be installed at the top of foundation walls beneath the sill plate to discourage termite entry.

        Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
        Figure 1. Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7) (Source: Courtesy of PNNL). 

         

        Training
        Right and Wrong Images
        Image
        Wrong – There is no foam gasket or air seal between the sill plate and masonry foundation.
        Wrong – There is no foam gasket or air seal between the sill plate and masonry foundation.
        Image
        Right – There is a foam gasket installed between the sill plate and foundation.
        Right – There is a foam gasket installed between the sill plate and foundation.
        Image
        Wrong – The caulk is too far from the sill plate to properly air seal.
        Wrong – The caulk is too far from the sill plate to properly air seal.
        Image
        Right – The sill plate was sprayed with foam prior to installation atop foundation.
        Right – The sill plate was sprayed with foam prior to installation atop foundation.
        Image
        Wrong – There is no foam gasket or air seal between the sill plate and masonry foundation.
        Wrong – There is no foam gasket or air seal between the sill plate and masonry foundation.
        Image
        Wrong – Foam was sprayed at exterior sheathing and sill plate connection, leaving gaps beneath sill plate.
        Wrong – Foam was sprayed at exterior sheathing and sill plate connection, leaving gaps beneath sill plate.
        Image
        Right – Spray foam was installed at the sheathing intersection as well as the sill plate to sub-floor connection.
        Right – Spray foam was installed at the sheathing intersection as well as the sill plate to sub-floor connection.
        Image
        Right – All penetrations through the sill plate are caulked or foamed.
        Right – All penetrations through the sill plate are caulked or foamed.
        Image
        Right - Seal the sill plate to the rim joist with caulk.
        Right - Seal the sill plate to the rim joist with caulk.
        Image
        Right - A termite shield and a sill gasket are installed between the sill plate and the foundation on a raised slab foundation.
        Right - A termite shield and a sill gasket are installed between the sill plate and the foundation on a raised slab foundation.
        Image
        Right - Make concrete masonry unit foundations more termite resistant by using a solid masonry block or bond beam for the top course, installing a termite shield, and using a borate-treated sill plate.
        Right - Make concrete masonry unit foundations more termite resistant by using a solid masonry block or bond beam for the top course, installing a termite shield, and using a borate-treated sill plate.
        Videos
        CAD
        CAD Files
        Conceptual air sealing strategy - lower wall section
        Conceptual air sealing strategy - lower wall section
        Download: DWG PDF
        Compliance

        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 Single-Family New Homes, Version 3/3.1/3.2 (Rev. 13)

        National Rater Field Checklist

        Thermal Enclosure System.
        4. Air Sealing (Unless otherwise noted below, “sealed” indicates the use of caulk, foam, or equivalent material). 
        4.3 Above-grade sill plates adjacent to conditioned space sealed to foundation or sub-floor. Gasket also placed beneath above-grade sill plate if resting atop concrete / masonry & adjacent to cond. space.27, 28

        Please see the ENERGY STAR Single-Family New Homes National Rater Field Checklist for relevant footnotes and additional information. 

        Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in in your state.

         

        DOE Zero Energy Ready Home

        Version 1, Rev. 07, Rev. 08, Rev. 09, and Version 2

        Exhibit 1 Mandatory Requirements.
        Exhibit 1, Item 2) (Item 1) in Version 1, Rev. 07 and Rev. 08) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.

         

        2009 International Energy Conservation Code (IECC)

        Residential Requirements

        Section 402.4.1 (Mandatory) specifies areas of the building thermal envelope that must be air sealed to limit infiltration.

        Commercial Requirements

        Section 502.4.3 (Mandatory) specifies areas of the building envelope that must be air sealed to limit infiltration.

        201220152018, and 2021 IECC

        Residential Requirements

        Section R402.4.1.1 (Mandatory) specifies areas of the building thermal envelope that must be air sealed to limit infiltration.

        Commercial Requirements

        Section C402.5.1.1 (C402.4.1.1 in 2012 IECC) (Mandatory) specifies areas of the building thermal envelope that must be air sealed to limit infiltration.

        Retrofit:  2009, 2012, 2015, 2018,  and 2021 IECC

        Section 101.4.3 (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.

         

        ASHRAE 90.1 - 2010, 2013, 2016, and 2019

        Section 5.4.3.1.2 (Mandatory) specifies areas of the building envelope that must be air sealed to limit infiltration.  

         

        20092012, 20152018 IRC, and 2021 IRC

        Section N1102.4.1.1 (N1102.4.1 in 2009 IRC) Specifies areas of the building envelope that must be air sealed to limit infiltration.

        R403.1.6. Sill plates and sole plates shall be protected against decay and termites where required by sections R317 and R318.

        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.

        Retrofit
        Existing Homes

        SCOPE

        In existing homes assess the foundation systems as described in the guide titled Pre-Retrofit Assessment of Crawlspaces and Basements. Remove objects obscuring access to the seam between the foundation and the sill plate and the space above the sill plate where the rim joist (also called a band joist) is located. Clearing this area may involve rolling back batt insulation that is stuffed into the bays where floor joists sit on the sill or rolling back and securing floor insulation that sits between the floor joists. Carefully clean and seal the seam between the foundation and the sill plate and the space above the sill plate where the rim joist is located. Seal and flash all penetrations through the rim joist or sill plate.

        Air sealing can impact indoor air quality and the air available for combustion appliances to work properly. Before starting the air sealing, read and conduct the assessments described in the guides Pre-Retrofit Assessment of Combustion Appliances and the Pre-Retrofit Assessment of Hazardous Materials.

        All global worker safety and air sealing health and safety specifications in DOE’s Standard Work Specifications (SWS) should be followed. See the SWS specifications for air sealing basements and crawl spaces and combustion safety.

        DESCRIPTION

        The best way to air seal the sill plate is to place a sill sealer (also called a sill gasket) on the concrete before laying the sill plate over the foundation. A sill seal product that covers the whole sill plate area is preferable because of its waterproofing capability and inherent uniformity. However, this approach only works when there is access to the sill before the sill plate is mounted. For existing homes this approach only works during remodels where the structure is torn down to the foundation, or when room additions include a new foundation.

        Although it will not provide waterproofing, sills can still be air sealed in existing homes with caulk or spray foam if the seam between the foundation and the sill plate is accessible, such as crawlspaces and unfinished basements. Before sealing, thoroughly clean all surfaces to receive sealants or insulation and ensure all dry rot or other damage has been repaired. For more information on air sealing sill plates in existing buildings, please see the Water Managed Existing Sill Beams and Sill Plates guide.  An assessment guide for foundation systems is available in the Pre-Retrofit Assessment of Crawlspaces and Basements assessment guide.

        Caulk and/or spray foam can be used to seal (and insulate when spray foam is used) the seam where the sill plate sits on the foundation, as well as the area where the subfloor and rim joist sit on the sill plate.

        Any penetrations through exterior walls must be sealed. See the Air Sealing Electrical Wiring and Air Sealing Plumbing and Piping guides for more information.

        Seal and flash all penetrations through the rim joist or sill plate. All surfaces must be cleaned before applying sealants. The photos in Figures 1 and 2 show how caulk and spray foam are applied. Surfaces must be clean and free of dust, dirt, and grease for the sealants to stick.

        Caulk is used to seal the seams around the rim joist.
        Figure 1. Caulk is used to seal the seams around the rim joist.

         

        Spray foam is used to seal the seam where the sill plate sits on the foundation.
        Figure 2. Spray foam is used to seal the seam where the sill plate sits on the foundation.

        Rigid foam is another option for insulating the juncture of the rim joist and the sill plate as shown in Figures 3 and 4. For more guidance on this approach, see the guide titled Rigid Foam Board Insulation for Existing Band Joists.

        It may not be possible to apply sealants directly to the seam between the foundation and the sill plate in homes with existing concrete slabs. However, it may be possible to remove the baseboard around the bottom of exterior walls within conditioned spaces and seal the crack between the wall and the floor. This crack may have carpeting and other flooring in it. If it can be done without damaging the visible portion of the carpet, remove carpet fibers from the crack before filling the crack with caulk. Be sure to replace any baseboard removed for the project. Be careful to keep sealants off the floor and wall finishes.

        Kitchen and bath cabinets, stairs, and other built-in components may block access. Seal around the cabinets and the joints within the cabinets. Investigate removing the toe kick from cabinets to reach the intersection of the wall and the floor. Kitchen and bath remodels are a perfect time to access this seam. Be sure to replace any toe kicks removed for the project.

        Rigid foam insulation may be used to seal and insulation the interior side of the rim joist.
        Figure 3. Rigid foam insulation may be used to seal and insulate the interior side of the rim joist.

         

        This figure shows how rigid foam insulation can be used with spray foam to seal the rim joist, including penetrations.
        Figure 4. This figure shows how rigid foam insulation can be used with spray foam to seal the rim joist, including penetrations.

        Pay attention to cantilevered floor cavities for balconies, bay windows, or other bump outs that extend past the foundation to the exterior. The open bays where the floor joists extend past the foundation must be filled with rigid insulation or another sheet material and insulation. See the Cantilevered Floor guide for more information. The photo in Figure 5 shows how rigid foam insulation held in place with spray foam may be used to seal open bays in cantilevered floors. Once the open bays are sealed the floor joists may be filled with insulation. If it is accessible, seal the floor surface above the cantilevered floor joists. Batt insulation must be installed before exterior sheathing is attached to the bottom of the floor joists. If the cantilevered space is already enclosed, blown in insulation is an option.

        Carefully seal walls separating conditioned spaces and garages as exterior walls, caulking all cracks on both sides of the wall, including the seam between the bottom plate of the wall and the foundation or subfloor.

        Existing surfaces may be finished with paint containing lead, especially in homes built before 1978. Old plaster may contain asbestos. The Pre-Retrofit Assessment of Hazardous Materials guide contains more information.

        Rigid foam insulation and spray foam are used to seal the open joist bays below a cantilevered floor.
        Figure 5. Rigid foam insulation and spray foam are used to seal the open joist bays below a cantilevered floor.

         

        COMPLIANCE 

        See Compliance tab. 

        More

        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
        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 Michael C,
        Gilbride Theresa L,
        Hefty Marye G,
        Cole Pam C,
        Adams Karen T,
        Butner Ryan S,
        Ortiz S J,
        Love Pat M
        Organization(s)
        Pacific Northwest National Laboratory,
        PNNL,
        Oak Ridge National Laboratory,
        ORNL
        Publication Date
        Description
        Report describing measures that builders in mixed-humid climates can use to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.
        Author(s)
        Building Science Corporation
        Organization(s)
        BSC
        Publication Date
        Description
        Information sheet with details on a building enclosure designed for Albuquerque, NM, as an example for building enclosures built for hot-dry and mixed-dry climates.
        Author(s)
        Koel
        Organization(s)
        American Technical Publishers
        Description
        Website with instructional material for career and technical education.
        Author(s)
        Robinson Bill
        Organization(s)
        Journal of Light Construction
        Publication Date
        Description
        Article describing various types of caulks and sealants, their formulas and best uses.
        *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.

        Sales
        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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