Floor Above Garage
Air seal the floor above a garage when there is living space above the garage and make sure floor insulation is in full contact with the underside of the subfloor.
- Seal all seams, gaps, and holes in the subfloor air barrier with caulk or foam.
- Air seal rim joists and any holes in the top plate of the garage walls.
- Install insulation without misalignments, compressions, gaps, or voids.
- Install supports to keep insulation in permanent contact with the air barrier above, for example, metal staves for batt insulation or netting for blown insulation.
- If spray foam insulation is used for the floor cavity insulation, the spray foam can serve as the air barrier if it is at least 5.5 inches thick if open-cell or at least 1.5 inches thick if closed-cell spray foam insulation.
- Consider a combination of spray foam and fibrous insulation to thoroughly air seal and meet insulation R-value requirements.
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.
Even when a garage is attached to the home, it is still outside the thermal envelope of the home, so the walls and ceiling separating it from the rest of the home must be insulated and air sealed just like any exterior walls or floors above unconditioned space. For the Insulation installed in the floor above a garage to be effective, it must be in full contact (continuous alignment) with the subfloor above and with the rim joists on all sides and any seams or holes in the subfloor and rim joists must be sealed. This air sealing provides a continuous air barrier which serves two purposes: it keeps wind from blowing through the insulation and robbing it of its thermal value and, even more importantly, it prevents garage air pollutants like car exhaust and chemical fumes from migrating into the home (EPA 2008).
When the insulation is not in contact with the subfloor (as shown in Figure 1), it creates space for air to flow, either from unsealed exterior walls or from convective loops of air currents. The moving air pulls heat from the floor system, robbing the insulation of its effectiveness and causing cold floors above. The solution to eliminating these thermal short circuits is two-fold: First, completely air seal the floor system, paying particular attention to sealing the band/rim joist area to create a continuous air barrier. Second, install the ceiling insulation in full alignment (continuous contact) with this insulation (EPA 2008).
How to Insulate and Airseal the Floor above an Attached Garage
- Install a subfloor that can serve as a continuous air barrier between the garage and the rooms above. In most cases, this air barrier will be plywood or OSB floor sheathing. Install the subfloor sheathing panels according to APA Sturd-I-Floor recommendations, which includes the following (APA 2011):
- Install subfloor in panel widths that align with the framing (typically 16-, 20-, or 24-inches on-center).
- Stagger subfloor panel end joints.
- Use tongue-and-groove subfloor panels or install blocking beneath panel joints.
- Apply construction adhesive or caulk at panel seams and between subfloor panel and framing members.
2. Air seal the band and rim joists and any penetrations.
- Block off any open floor joists running from the garage ceiling to under other parts of the home to prevent the infiltration of airborne pollutants (EPA 2008). See the guide Garage Rim/Band Joist Adjoining Conditioned Space for more information. Use an air barrier material such as plywood, sheathing, rigid foam, or OSB (see Figure 4). Do not use batt insulation for air sealing.
- If I-joists are used, the blocking material must be cut to fit the shape. This can be done with filler strips as shown in Figure 4. Or, the corners of the blocking may be cut to fit around the I-joist flanges, as shown in Figure 5.
- Seal the edges of the blocking with a one- or two-part foam sealant or caulk. Foam sealant will work better (and last longer) than caulk. Spray foam can be used to cover the whole air barrier (Figure 6) to fill small voids and cracks to effectively stop air flow, while also providing additional R-value (DOE 2012).
3. Install insulation in the floor joists.
- Insulation should be fully "aligned" with the air barrier, i.e., in full contact with the subfloor above. There can be no gaps between the insulation and the sheathing above it (EPA 2011).
- Batt insulation should fit tightly between the floor joists but avoid gaps, compressions, or voids. Batts should be fully lofted (not crammed or compressed into the space, see Figure 6). Batts should be cut lengthwise to fit narrow joist bays, and split to fit neatly around electrical wiring running across joist bays. See the guide Insulation Installation Achieves RESNET Grade 1 for more on quality installation.
- Blown-in fiberglass or cellulose can be used for insulating the floor above a garage. It is an effective way to fill the voids when webbed floor trusses are used. Install the blown-in insulation to the correct density to prevent settling. The drywall must be sufficient to hold the weight of the insulation; check with the insulation manufacturer and installer to determine if the joist depth, joist spacing, and weight of the insulation are compatible (EPA 2008).
Spray foam insulation can be used to insulate the entire floor above a garage (as well as the band joist). Spray foam provides high R-value and a continuous air barrier in one labor-saving application. To qualify as an air barrier, open-cell spray foam must have a finished thickness ≥ 5.5 inches and closed-cell spray foam must have a finished thickness ≥ 1.5 inches (EPA 2011).
4. Support insulation. Once installed, the insulation must be well supported to ensure it remains in contact with the subfloor above it. If the insulation fills the floor cavity, ceiling drywall will support it. If ceiling drywall will not be installed, or if batt insulation does not fill the entire joist cavity, insulation stays must be installed to keep the insulation in continuous contact with subfloor above.
Blower Door Testing
Conducted as part of whole-house energy performance testing, may help indicate whether air leakage at the floor has been successfully sealed.
An infrared camera also may be used to determine air leakage at the floor over a garage, if a sufficient temperature difference exists between the unconditioned garage and the conditioned space above the garage. For best results, scan twice. First, scan under static conditions before blower door testing has been conducted. This will allow the technician to evaluate the integrity of insulation behind the drywall if the garage ceiling has been finished. Conduct a second scan with the blower door running in depressurization mode and the door between the house and the garage open. This will demonstrate the integrity of the air barrier, showing where air leakage has infiltrated the framing and seeped through insulation.
With the blower door pressurizing, the garage door closed and the door to the house open, check for air leaks in the floor and near the rim joist with a smoke pencil. A smoke trail moving away from the smoke pencil indicates a leak to the unconditioned space that should be sealed.
In cold climates, avoid plumbing in floors over garages. Plumbing pipes should not be run through floors over garages that are in unconditioned space because the pipes could freeze. Builders sometimes try other solutions that can lead to mold problems. For example, as shown in the photo, the builder has actually installed a supply duct in the floor cavity to heat this space and prevent the pipes from freezing. This duct will pressurize that space with warm, humid air, and when that warm, humid air comes in contact with cold surfaces, it can lead to condensation, which in turn can lead to mold-related problems. It is always best practice in cold climates to avoid putting plumbing fixtures in the building cavities over garages.
In cold climates, plumbing pipes should not be located in the building cavities over the garage because of the potential for pipes to freeze. This photo shows how a builder has tried to solve the problem by installing a supply duct to heat the space. However, when such warm, humid air meets a cold surface, it can condensate, resulting in mold.
Exhibit 2: DOE Zero Energy Ready Home Target Home. Certified under ENERGY STAR Qualified Homes Version 3. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.
International Energy Conservation Code (IECC) Climate Regions
ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), Rater Field Checklist, Thermal Enclosure System
2. Fully-Aligned Air Barriers.5 At each insulated location below, a complete air barrier is provided that is fully aligned as follows:
Floors: At exterior vertical surface of floor insulation in all climate zones and, if over unconditioned space, also at interior horizontal surface including supports to ensure alignment. See Footnotes 10 & 11 for alternatives.9, 10, 11
2.6 Floors above garages, floors above unconditioned basements or crawlspaces, and cantilevered floors
(5) For purposes of this Checklist, an air barrier is defined as any durable solid material that blocks air flow between conditioned space and unconditioned space, including necessary sealing to block excessive air flow at edges and seams and adequate support to resist positive and negative pressures without displacement or damage. EPA recommends, but does not require, rigid air barriers. Open-cell or closed-cell foam shall have a finished thickness ≥ 5.5 in. or 1.5 in., respectively, to qualify as an air barrier unless the manufacturer indicates otherwise. If flexible air barriers such as house wrap are used, they shall be fully sealed at all seams and edges and supported using fasteners with caps or heads ≥ 1 in. diameter unless otherwise indicated by the manufacturer. Flexible air barriers shall not be made of kraft paper, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.
(9) EPA highly recommends, but does not require, an air barrier at the interior vertical surface of floor insulation in Climate Zones 4-8.
(10) Examples of supports necessary for permanent contact include staves for batt insulation or netting for blown-in insulation. Alternatively, supports are not required if batts fill the full depth of the floor cavity, even when compression occurs due to excess insulation, as long as the R-value of the batts has been appropriately assessed based on manufacturer guidance and the only defect preventing the insulation from achieving the required installation grade is the compression caused by the excess insulation.
(11) Alternatively, an air barrier is permitted to be installed at the exterior horizontal surface of the floor insulation if the insulation is installed in contact with this air barrier, the exterior vertical surfaces of the floor cavity are also insulated, and air barriers are included at the exterior vertical surfaces of this insulation.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
Exhibit 2: DOE Zero Energy Ready Home Target Home. Certified under ENERGY STAR Qualified Homes Version 3. Insulation levels shall meet or exceed the 2012 IECC (Table R402.1.1) and achieve Grade 1 installation, per RESNET standards. Infiltration (ACH50): Zones 1-2: 3; Zones 3-4: 2.5; Zones 5-7: 2; Zone 8: 1.5. Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol. Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 2012 IECC – Table 402.2.6.
Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Floors: Air barrier is installed at any exposed edge of insulation.* Table 402.4.2, Air barrier and thermal barrier: Air permeable insulation is not used as a sealing material.*
Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria, Floors: Air barrier is installed at any exposed edge of insulation.* Table N1102.4.2, Air barrier and thermal barrier: Air permeable insulation is not used as a sealing material.*
Table R402.4.1.1 Air Barrier and Insulation Installation, Floors: Insulation in floors (including above garage and cantilevered floors) is installed to maintain permanent contact with underside of subfloor decking. A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material. 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.*
Table N1220.127.116.11 Air Barrier and Insulation Installation, Floors: Insulation in floors (including above garage and cantilevered floors) is installed to maintain permanent contact with underside of subfloor decking. A continuous air barrier is installed in the building envelope including rim joists and exposed edges of insulation. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material. 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.
Fully Aligned Air Barriers = Whole-House Draft Barrier