Air Sealing Sill Plates

Scope

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

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, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

For a home to perform efficiently, the walls, ceiling, and foundation that comprise the building shell must be connected to 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 sealed with an appropriate sealing material as described below. The sill plate where the wall meets the concrete foundation is especially susceptible to air leakage for two reasons: because the concrete surface is sometimes rough, preventing a smooth seam between the foundation and the sill plate and because of the stack effect, which 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 horizontally directly on top of the foundation wall. It consists of usually one layer of 2x6 or 2x8 pressure-treated lumber. In platform construction, the band joist and floor joists rest on 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. 

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. 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.

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 is setback 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 termite shield if desired. The termite shield is a strip of 26-gauge aluminum, copper, or galvanized sheet metal laid along the outer edge of foundation wall. The outer edge hangs 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. 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 and bolt down with washers and nuts.
  5. Install rim joists. Caulk at rim joist-sill plate seams (BSC 2009c).

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 Reference

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 Reference

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 Reference

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 Reference

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

ENERGY STAR Version 3, (Rev. 07)

In Climate Zones 1 through 3, a continuous stucco cladding system adjacent to sill and bottom plates is permitted to be used in lieu of sealing plates to foundation or sub-floor with caulk, foam, or equivalent material.

 

climate zone map

 

 

Training

Right and Wrong Images

Presentations

None Available

Videos

  1. Sill Plates (1)
    Publication Date: July, 2015
    Courtesy Of: NYSERDA

    Video describing how to properly air seal sill plates.

  2. Sill Plates (2)
    Publication Date: July, 2015
    Courtesy Of: Risinger Homes

    Video describing how to insulate and air seal sill plates.

  3. Sill Plates (3)
    Publication Date: July, 2015
    Courtesy Of: Train2Build

    Video describing how to properly air seal sill plates.

CAD Images

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): 

4.3 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 conditioned space25,26 

Footnotes:

(25) Existing sill plates (e.g., in a home undergoing a gut rehabilitation) on the interior side of structural masonry or monolithic walls are exempt from this Item. In addition, other existing sill plates resting atop concrete or masonry and adjacent to conditioned space are permitted, in lieu of using a gasket, to be sealed with caulk, foam, or equivalent material at both the interior seam between the sill plate and the subfloor and the seam between the top of the sill plate and the sheathing.

(26) In Climate Zones 1 through 3, a continuous stucco cladding system adjacent to sill and bottom plates is permitted to be used in lieu of sealing plates to foundation or sub-floor with caulk, foam, or equivalent material.

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

Section 402.4.1 Building thermal envelope. Joints (including rim joist junctions), attic access openings, penetrations, and all other such openings in the building envelope that are sources of air leakage are sealed with caulk, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.*

2009 IRC

Section N1102.4.1 Building thermal envelope. Joints (including rim joist junctions), attic access openings, penetrations, and all other such openings in the building envelope that are sources of air leakage are sealed with caulk, gasketed, weatherstripped or otherwise sealed with an air barrier material, suitable film or solid material.*  

2012 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.*  

2012 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.* 

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

2015 IECC

2015 IRC

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

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 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 see the SWS specifications on 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. 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 applied at the seam where the sill plate sits on the foundation, and it can be used to seal (and insulate when spray foam is used) the area where the subfloor and rim joist sit on the sill plate.

Any penetrations through exterior walls must be sealed. See the guides on air sealing electrical wiring and plumbing penetrations.

Use caulk or 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.

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 of 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.

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 guide on cantilevered floors 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, dense pack, 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 home built before 1978. Old plaster may contain asbestos. The Pre-Retrofit Assessment of Hazardous Materials guide contains more information.


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


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


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


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


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

 

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

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: February, 2013

    Case study about new home construction in the marine climate that achieved 50% savings over the 2004 IECC.

  2. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: February, 2013

    Case study about a new construction building project of 20 homes that earned HERS scores that represent greater than 50% energy savings in heating and cooling over the 2004 IECC.

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, Adams, Butner, Oritz, Love
    Organization(s): PNNL, ORNL
    Publication Date: September, 2011
    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.
  3. Author(s): BSC
    Organization(s): BSC
    Publication Date: April, 2009
    Information sheet with details on building enclosures for hot-dry and mixed-dry climates.
  4. Author(s): Koel
    Organization(s): American Technical Publishers
    Website with instructructional material for career and technical education.
  5. Author(s): BSC
    Organization(s): BSC
    Publication Date: September, 2009
    Information sheet about air sealing.
  6. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2017

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

  7. Author(s): EPA
    Organization(s): EPA
    Publication Date: December, 2015

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

  8. 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.

Contributors to this Guide

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

Last Updated: 07/19/2017