Air Sealing Attached Garage

Scope

Air seal and insulate the rim and band joists of walls separating an attached garage from the home’s conditioned space.
Air seal and insulate the rim and band joists of walls separating an attached garage from the home’s conditioned space.

Ensure that the garage is separated from the conditioned space of the home by a continuous rigid air barrier.

  • Seal all seams, gaps, holes, and openings in the air barrier with caulk, foam, rigid air barrier material before installing the insulation.

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

Isolating attached garages from the living space is critical for preventing the potential infiltration of carbon monoxide and other contaminants into the dwelling. Open joist bays above the garage that extend into living spaces are an unwanted air pathway. Cracks between and around the boards of the rim joist, the top plate, and the sill plate-foundation wall intersections are other areas where air can flow through if seams aren’t adequately sealed. In addition, certain conditions in the home can cause the home to become depressurized, making it even more likely for garage air to be drawn into the home through leaks in and around the rim joists. Depressurization can occur when the house is airtight and an exhaust fan, range hood, clothes dryer, or combustion appliance is operated, if adequate makeup air is not provided to the house through a fresh air intake (a duct that brings outside air to the return side of the air handler).

Walls and ceilings shared by the garage and living space must be air sealed and insulated.

Figure 1. Walls and ceilings shared by the garage and living space must be air sealed and insulated. (Image courtesy of Steven Winter Associates)

Walls and floors adjoining garage spaces need to be sheetrocked (typically with 1/2-inch-thick Type X gypsum board) in accordance with local fire codes, but this is not the same as air sealing. All ceiling and wall penetrations (wiring, piping, ductwork, etc.) need to be sealed with appropriate materials, such as caulk or spray foam. All joist cavities between the garage and adjoining living spaces should be blocked with rigid material or the framing should be designed so that rim joists or floor joists will serve as a naturally occurring air block at the shared wall. These same air-sealing concepts apply to overhangs and porch roofs.

To provide an air barrier between the garage and the adjoining conditioned space, solid blocking is often used to air seal joist bay openings spanning over the garage and conditioned space. A rigid material like rigid foam board, drywall, OSB, or plywood can be cut to fit each joist bay opening. Each piece must be cut to fit then nailed and caulked or spray foamed into place, which is a labor-intensive process.

The best option would be to design the home to isolate the attached garage through the use of framing members. Ideally the framing would be designed so that ceiling joists above the garage run parallel to the shared wall so that a ceiling joist can serve as a solid air barrier above the shared wall. Where open bays would span the shared walls, the floor joists can be cut so that they terminate on either side of a rim joist installed over the shared wall. The joints between the mud sill and rim joist at the foundation line of the garage-to-house wall should be sealed. The drywall separating the garage from the house should be sealed to the framing members at the top plate, bottom plate, corners, and seams.

How to Air Seal between the Garage and Living Space

In all instances discussed below, air sealing of seams and cracks in framing with an appropriate, compatible sealant is required.

1. Air seal the rim joist of the wall shared by the garage and the house. (See the guide Garage Rim Band Joist for more details.)

a. Design walls adjoining garages so that the rim joist board runs parallel to the common wall, providing a continuous natural air barrier.

b. Where ceiling joists run perpendicular to the adjoining wall (see Figure 2), one option is to install a continuous rim joist to separate the two areas with separate but aligned ceiling joists on each side of the rim joist (see Figure 3 and Figure 4).

c. Another option is to install solid blocking material in the joist bays over the common wall. Cut rectangles of rigid blocking material (plywood, polyisocyanurate, extruded polystyrene, etc.) to fit each floor joist bay cavity. Install a backstop for the blocking material by tacking furring strips to the joists in line with the foundation or house wall. Insert rigid pieces into each joist bay and fasten with caulk or nails (Figure 5). When using I-joists, make sure to cut the blocking to fill the irregular shape of the opening (Figure 6). Also seal holes in open-web floor trusses at the shared wall, if needed (Figure 7). Use caulk or spray foam to air seal all four edges in each bay (Figure 8). Make sure to completely air seal around the rigid air barrier to prevent moist air from reaching and condensing on the rim joist.

d. Insulate the rim joist with additional rigid foam that is caulked or foamed into place or with spray foam. Use urethane spray foam insulation to cover the rim joist, and seams with the top plate below and subfloor above (see Figure 9). Medium-density (closed-cell, 2 pounds/cubic foot) or low-density (open-cell, 0.5 pounds/cubic foot) foams provide acceptable results. Open-cell foams might require additional vapor and condensation control measures in IECC Climate Zone 6 and higher. Foam can be applied by a spray foam subcontractor or use two-part spray foam kits.

Spray foam in band joists is typically concealed between floors so no other thermal barrier is required; however, the International Residential Code (IRC) allows the spray foam at rim joists to be exposed in basement and crawlspace applications (i.e., without a 15-minute thermal barrier such as drywall) as long as the thickness is less than 3.25 inches and has a density range of 0.5 to 2.0 pounds per cubic foot (see 2009 IRC R316.5.11). Closed-cell, 2-PCF spray foams were approved in the 2003 IRC and open-cell 0.5-PCF foams were approved in the 2009 IRC, along with any intermediate densities (BSC 2009).

Climate Note: Although open-cell spray foam is acceptable in this application per code, closed-cell spray foam is preferred in hot-humid or extreme cold climates (IECC Climate Zones 1A, 2A, 7, and 8) (Zoeller 2009).

2. Caulk or spray foam the garage slab-foundation wall junction. (See the guide Reduce Pest Intrusion for more on foundation sealing.)

3. Seal all penetrations through the shared walls and ceilings. See the Building America Solution Center guides on air sealing electrical wiring and plumbing penetrations. Other guides are also available that cover other air sealing strategies. Use “Search” to find specific air sealing topics, such as ceilings, and others.

Use gaskets, airtight drywall technique, etc., to make the common wall and ceiling airtight. Consider a “flash” seal approach - spray foam the entire ceiling and/or inter-zonal walls of the garage to air seal any cracks, holes, or seams. Then add batt or blown insulation to meet the insulation R-value requirement (Figure 10), at a cost savings compared to using spray foam alone to meet the insulation requirement. Cover the ceiling insulation with taped and mudded drywall.

4. Other Important Considerations:

a. Install a self-closing, insulated, metal, fire-rated door with a good weather seal between the living space and the garage.

b. If the air handler for a central furnace must be located in the garage, it needs to be in an air-sealed closet. (See the report Air Sealing Mechanical Closets in Slab-On-Grade Homes.) Do not have supply or return registers in the garage. If ductwork is located in the garage ceiling to service rooms above, make sure it is encapsulated with closed-cell spray polyurethane foam to ensure a complete air barrier. (See the report Buried and/or Encapsulated Ducts.)

c. Install a passive vent from the garage to the outside. Consider installing a timer-operated exhaust fan that vents from the garage to the outside.

When ceiling joists over a garage run perpendicular to the adjoining wall, the joist bays must be blocked and sealed to prevent garage fumes from entering the living space

Figure 2. When ceiling joists over a garage run perpendicular to the adjoining wall, the joist bays must be blocked and sealed to prevent garage fumes from entering the living space. (Image courtesy of Steven Winter Associates)

A continuous rim joist separates the garage from the living space

Figure 3. A continuous rim joist separates the garage from the living space. Reference

The I-joist is continuous along the shared wall and serves as a natural air barrier between the garage and the house

Figure 4. The I-joist is continuous along the shared wall and serves as a natural air barrier between the garage and the house. (Image courtesy of Steven Winter Associates)

Insert rigid blocking pieces into each joist bay and fasten with caulk or nails

Figure 5. Insert rigid blocking pieces into each joist bay and fasten with caulk or nails. (Image courtesy of Steven Winter Associates)

When using I-joists, make sure to fill in the gaps on each side of the blocking material to air seal the joist bay

Figure 6. When using I-joists, make sure to fill in the gaps on each side of the blocking material to air seal the joist bay. (Image courtesy of Steven Winter Associates)

Foam holes in open-web floor trusses to completely seal the rim joist

Figure 7. Foam holes in open-web floor trusses to completely seal the rim joist. (Image courtesy of Steven Winter Associates)

Use caulk or spray foam to air seal all four edges of the blocking material in each joist bay

Figure 8. Use caulk or spray foam to air seal all four edges of the blocking material in each joist bay. (Image courtesy of Steven Winter Associates)

Spray foam insulates the rim joist and air seals the subfloor-rim joist and rim joist-top plate connections

Figure 9. Spray foam insulates the rim joist and air seals the subfloor-rim joist and rim joist-top plate connections. (Image courtesy of Steven Winter Associates)

Use a flash and batt approach to insulate and air seal the garage ceiling

Figure 10. Use a flash and batt approach to insulate and air seal the garage ceiling. (Image courtesy of Steven Winter Associates)

Ensuring Success

If the home has an attached garage, visually inspect for cracks or improper sealing along the rim joist above walls separating the garage from the home. For joist bays that extend from over the garage ceiling to over or under living areas of the house, the joist bay cavities should be blocked off, air sealed, and insulated. Rim joists that run parallel to the shared wall should be air sealed and insulated at the rim joist.

Blower door testing conducted as part of the whole-house energy performance testing can indicate whether the rim joists have been successfully air sealed. Blower door testing can also help determine if the home is depressurized compared to the garage; if so, a means of supplying makeup air to the home may be called for to prevent garage fumes from being pulled into the home.

The following actions are also recommended to ensure that garage air is separated from house air:

  • Visually inspect for cracks along the base of garage walls that adjoin living space and along sill plates on top of foundation walls on adjoining walls.
  • Visually inspect that all penetrations through adjoining walls and garage ceilings below living spaces are sealed.
  • Test the seal tightness of doors linking the garage with the rest of the home.
  • Best practice is to not install HVAC equipment in the garage. If a furnace is installed in the garage, it should be sealed combustion and direct vent. Visually inspect that the furnace cabinets and ducts are air sealed with mastic or metal tape or, preferably, that the furnace is installed in an air-sealed closet. No return air registers should be installed in the garage. Any ducts installed in the garage should be sealed with mastic and tested for air tightness.

Climate

If the rim joists are to be sealed with spray foam, although both open-cell and closed-cell spray foam are acceptable in this application, closed-cell spray foam is preferred in hot-humid or extreme cold climates (IECC Climate Zones 1A, 2A, 7, and 8) (Zoeller 2009).

See the Compliance tab for more climate zone requirements.

IECC climate zone map

Training

Right and Wrong Images

Presentations

  1. Zero Energy Ready Home Training
    Author(s): Rashkin
    Organization(s): DOE

Videos

None Available

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.

DOE Zero Energy Ready Home

 The U.S. Department of Energy (DOE) Zero Energy Ready Home program requires that builders comply with the U.S. Environmental Protection Agency (EPA) Indoor airPLUS program criteria. The Indoor airPLUS checklist (Item 4.3) requires that builders not locate air handling equipment or ductwork in garages but notes that ducts and equipment may be located in building cavities adjacent to garage walls or ceilings if the cavities are separated from the garage space with a continuous air barrier. The Indoor airPLUS Construction Specifications (Item 5.4) requires that homes with exhaust-only whole-house ventilation either are equipped with an exhaust fan or that the builder verify that the garage-to-house air barrier can maintain a pressure difference of greater than 45 Pascals while the home maintains a 50 Pascal pressure difference with respect to the outdoors, with all doors and windows closed during the blower door test.

The DOE Zero Energy Ready Home Target Home Exhibit 2 specifies that homes be whole house leakage tested and meet the following infiltration limits: Zones 1-2: ≤ 3 ACH50; Zones 3-4: ≤ 2.5 ACH50; Zones 5-7: ≤ 2; Zone 8: ≤ 1.5. Envelope leakage must be determined by an approved verifier using a RESNET-approved testing protocol.

ENERGY STAR Certified Homes (Version 3, Rev. 08)

 The ENERGY STAR Certified Homes Rater Field Checklist requires (in Item 3m Fully Aligned Air Barriers) that a complete air barrier that is fully aligned with insulation be installed in at each insulated location of the home including: Ceilings: at the interior or exterior horizontal surface of ceiling insulation Climate Zones 1-3; at the interior horizontal surface of ceiling insulation in Climate Zones 4-8; at the exterior vertical surface of ceiling insulation in all climate zones; Walls: at the exterior vertical surface of wall insulation in all climate zones; also at the interior vertical surface of wall insulation in Climate Zones 4-8; Floors: at the exterior vertical surface of floor insulation in all climate zones and, if over unconditioned space, also at the interior horizontal surface including supports to ensure alignment. It specifically indicates several areas requiring a complete air barrier including Item 2.6 floors above garages and Item 4.7 walls that separate attached garages from occupiable space sealed and, also, an air barrier installed and sealed at floor cavities aligned with these walls.

Rater Design Checklist Footnote: (6) Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, slab insulation shall also be installed at this interface to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this requirement, partners shall provide the detail to EPA to request an exemption prior to the home’s certification. EPA will compile exempted details and work with industry to develop feasible details for use in future revisions to the program. A list of currently exempted details is available at: energystar.gov/slabedge.

Rater Field Checklist Footnotes:

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.

6. All insulated ceiling surfaces, regardless of slope (e.g., cathedral ceilings, tray ceilings, conditioned attic roof decks, flat ceilings, sloped ceilings), must meet the requirements for ceilings.

7. All insulated vertical surfaces are considered walls (e.g., above and below grade exterior walls, knee walls) and must meet the air barrier requirements for walls. The following exceptions apply: air barriers recommended, but not required, in adiabatic walls in multifamily dwellings; and, in Climate Zones 4 through 8, an air barrier at the interior vertical surface of insulation is recommended but not required in basement walls or crawlspace walls. For the purpose of these exceptions, a basement or crawlspace is a space for which ≥ 40% of the total gross wall area is below-grade.

8. Exterior air barriers are not required for attic knee walls that are ≤ 24 in. in height if an interior air barrier is provided and insulation extends in all directions from the top of this interior air barrier into unconditioned space at the following levels: CZ 1-5: ≥ R-21; CZ 6-8: ≥ R-30.

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.

12. The minimum designated R-values must be achieved regardless of the trade-offs determined using an equivalent U-factor or UA alternative calculation, ...

13. Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, slab insulation shall also be installed at this interface to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this requirement, partners shall provide the detail to EPA to request an exemption prior to the home’s certification. EPA will compile exempted details and work with industry to develop feasible details for use in future revisions to the program. A list of currently exempted details is available at: energystar.gov/slabedge.

ASTM E1677-11

Standard Specification for Air Barrier (AB) Material or System for Low-Rise Framed Building Walls. This specification covers minimum performances and specification criteria for an air barrier material or system for framed, opaque walls of low-rise buildings. The provisions are intended to allow the user to design the wall performance criteria and increase air barrier specifications for a particular climate location, function, or design.

ABAA 07261

Self-Adhered Sheet Air Barrier. 2006. Air Barrier Association of America, Walpole, MA. This specification for self-adhered sheet air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

ABAA 07262

Fluid-Applied Air and Vapor Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for air barriers that are fluid-applied and also act as vapor barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

ABAA 07263

Closed Cell, Medium-Density Spray Polyurethane Foam Air Barrier. 2011. Air Barrier Association of America, Walpole, MA. This specification for closed cell, medium-density spray polyurethane foam air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

ABAA 07265

Fluid-Applied Vapor Permeable Air Barrier. 2012. Air Barrier Association of America, Walpole, MA. This specification for fluid-applied vapor permeable air barriers is developed by a professional association, the Air Barrier Association of America, to provide guidance to the design professional.

2009 IECC

Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, Garage separation: Air sealing is installed between the garage and conditioned spaces.* Table 402.4.2, Air barrier and thermal barrier: Exterior wall insulation is installed in substantial contact and continuous alignment with the air barrier. Air permeable insulation is not used as a sealing material.

2009 IRC

Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria, Garage separation: Air sealing is installed between the garage and conditioned spaces.* Table N1102.4.2, Air barrier and thermal barrier: Exterior wall insulation is installed in substantial contact and continuous alignment with the air barrier. Air permeable insulation is not used as a sealing material.

2012 IECC

Table R402.4.1.1 Air Barrier and Insulation Installation, Garage separation: Air sealing is installed between the garage and conditioned spaces. Table R402.4.1.1, Air barrier and thermal barrier: 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.

2012 IRC

Table N1102.4.1.1 Air Barrier and Insulation Installation, Garage separation: Air sealing is installed between the garage and conditioned spaces. Table N1102.4.1.1, Air barrier and thermal barrier: 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.

 

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.

Additional Scope Language for Retrofit Applications

Air seal the walls and ceilings of a garage that is attached to an existing home’s conditioned space and living areas.   

  • Determine which wall and ceiling assemblies in the garage are attached to the home’s living areas and inspect those assemblies for any cracks, holes, gaps, rot,  water damage, or deterioration.
  • Repair holes in ceilings or walls with sheet rock or plywood and seal to ensure a continuous air barrier. 
  • Remove and replace any sheet rock that is rotten or has extensive water damage.  
  • Use caulk or foam to seal any cracks or gaps. Sealants (e.g., caulk, fire-retardant caulk, fire-rated spray foam, etc.) should be compatible with all adjoining surfaces and meet the fire and air barrier specifications according to code. 
  • Alterations that expose the existing framing cavity may require the installation of additional insulation. See the Compliance tab for alterations and repairs to existing walls.

For more information on conditions that may be encountered when working with walls or ceilings in existing homes, see the pre-retrofit assessment guide on air sealing walls, windows, and doors.  

For more guidance on sealing walls, see the U.S. Department of Energy’s Standard Work Specifications (SWS).

Follow safe work practices as described in the Standard Work Specifications’ section on Global Worker Safety.

Additional Description Language for Retrofit Applications

The walls and ceilings separating the home from the garage may not have gotten the same attention to air sealing and insulating as the other exterior walls when the home was originally built because builders sometimes overlook the fact that these walls and ceilings are part of the home’s “building thermal envelope,” the exterior walls, floors, ceilings, and other building components that provide a boundary between conditioned space and the outdoors or unconditioned space.

Maintaining the integrity of this thermal envelope, especially in regard to isolating the existing attached garage from living space is critical for preventing the potential infiltration of carbon monoxide and other contaminants into the dwelling. Over time, cracks or gaps may appear along the joints and seams in the sheet rock (gypsum board), at the mud sill, rim joists, subfloors, bottom of the sheet rock, at ceiling-wall intersections, and other areas where air can flow through if cracks or gaps are not adequately sealed. There could also be unsafe conditions that have existed since the house was built. For example there could be open floor joist bays spanning from over the garage to over or beneath attached living spaces; these openings could allow garage fumes to enter adjoining rooms through cracks in subfloors or through leaks around sealing and wall penetrations. Any open joist bays must be closed off with solid blocking material and sealants as described in the Description tab.

Any HVAC equipment installed in the garage should be installed in an air-tight closet and there should be no supply or exhaust registers in the garage.

In addition, certain changes to the home can cause the home to become depressurized, making it more likely for garage air to be drawn into the home if there are leaks in the air barrier between the home and the garage. Depressurization can occur when the house is airtight and an exhaust fan, range hood, clothes dryer, or combustion appliance is operated, if adequate makeup air is not provided to the house through a fresh air intake (a duct that brings outside air to the return side of the air handler). Changes to the house that could increase the likelihood of depressurization include adding a new higher powered range hood fan, adding or replacing exhaust fans, cleaning out the clothes dryer duct, air sealing parts of the house, or adding a fireplace or other combustion appliance that does not have a sealed combustion chamber with a dedicated intake air duct.

To help ensure that an airtight barrier separates the house from the garage, inspect the common walls between the home and the garage. The garage can also be tested for pressure differences with respect to the house using a blower door test. These steps can be done by a home energy rater as part of a home energy assessment.

(Also see the Solution Center guides Floor above Garage, Insulating Existing Floors over Garage, Garage Rim/Band Joist Adjoining Conditioned Space, Rigid Foam Insulation Installed Between Existing House and Garage Walls, and No Ducts or Air Handlers Located in Garage.)

How to Air Seal between the Existing Garage and Living Space

  1. Locate and inspect the air barrier separating the garage from the conditioned space of the house at the home’s thermal envelope. Test for separation between the two using a blower door test. Air seal all seams, any leaks around penetrations, and any joist bay cavities as described in the Description tab.
  2. Replace any materials that show signs of rot or water damage. 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 lathe together. Wetting may also help reduce dust generation.
  3. Assume that paint on surfaces painted prior to 1978 contains lead. 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.
  4. Check the door leading from the garage into the house. If the door is more than 15 years old, it may be a hollow door. A door between the garage and the home should be considered an exterior door. It should be either a solid core or insulated metal, fire-rated door. It should be weather-stripped, have a tight-fitting sweep, and have an automatic door-closing hinge. See the Compliance information below for additional information.

Additional Compliance Language for Retrofit Applications

Alterations

2018 IECC and 2018 IRC

2018 IECC R502.1 Additions, General

Additions shall conform to the provisions of this code as those provisions relate to new construction without requiring unaltered portions of the existing building to comply with this code. Additions should not create an unsafe or hazardous condition or overload existing building systems.  An addition is deemed to comply with this code if the addition alone complies, if the existing building and the addition comply as a single building, or if the building with the addition does not use more energy than the existing building. Additions shall be in accordance with Sections R502.1.1 or R502.1.2.

2018 IECC R503.1 Alterations, General

Alterations shall conform to the provisions of this code as those provisions relate to new construction without requiring unaltered portions of the existing building to comply with this code. Alterations should not create an unsafe or hazardous condition or overload existing building systems. Alterations should be such that the existing building does not use more energy than the existing building prior to the alteration. Additions shall be in accordance with Section R503.1.1 or R503.2.

2018 IECC R503.1.1/2018 IRC N1109.1.1 Building Envelope.  Building envelope assemblies that are part of the alteration must comply with Sections R402.1.2/N1102.1.2 (Insulation and Fenestration Table) or R402.1.4/N1102.1.4 (U-factor Alternative), and Sections R402.2.1/N1102.2.1 through R402.2.12/N1102.2.12, R402.3.1/N1102.3.1, R402.3.2/N1102.3.2, R402.4.3/N1102.4.3 and R402.4.4/N1102.4.5.

Exception:  The following alterations need not comply with the requirements for new construction provided the energy use of the building is not increased:

  • Existing ceiling, wall, or floor cavities exposed during construction, provided that the cavities are filled with insulation
  • Construction where the existing ceiling, wall, or floor cavity is not exposed.

2015 IECC and 2015 IRC

2015 IECC R501.1.1/2015 IRC N1107.1.1 Additions, Alterations, or Repairs – General.  Additions, alterations, or repairs to an existing building or portion of a building should comply with Sections R502/N1108, R503/N1109, or R504/N1110.  Unaltered portions of the existing building are not required to comply.

2015 IECC R503.1/2015 IRC N1109.1 General.  Alterations to any building or structure should comply with the requirements of the code for new construction. Alterations should not create an unsafe or hazardous condition or overload existing building systems. Alterations should be such that the altered building or structure uses no more energy than the existing building or structure prior to the alteration.

2015 IECC R503.1.1/2015 IRC N1109.1.1 Building Envelope.  Building envelope assemblies that are part of the alteration must comply with Sections R402.1.2/N1102.1.2 (Insulation and Fenestration Table) or R402.1.4/N1102.1.4 (U-factor Alternative), and Sections R402.2.1/N1102.2.1 through R402.2.12/N1102.2.12, R402.3/1/N1102.3.1, R402.3.2/N1102.3.2, R402.4.3/N1102.4.3 and R402.4.4/N1102.4.5.

Exception:  The following alterations need not comply with the requirements for new construction provided the energy use of the building is not increased:

  • Existing ceiling, wall, or floor cavities exposed during construction, provided that the cavities are filled with insulation
  • Construction where the existing ceiling, wall, or floor cavity is not exposed.

2012 IECC and 2012 IRC

2012 IECC Section R101.4.3/2012 IRC N1101.3. 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. The following need not comply with the requirements for new construction provided the energy use of the building is not increased:

  • Existing ceiling, wall, or floor cavities exposed during construction, provided that these cavities are filled with insulation.
  • Construction where the existing roof, wall, or floor cavity is not exposed.

2012 IECC R101.4.5/2012 IRC N1101.4. Change in Space Conditioning.  Any non-conditioned that is altered to become conditioned space must be brought into full compliance with this code. (This means not only the altered assembly must be brought into compliance but the entire space or building would need to be brought into compliance.)

Air Sealing/Air Leakage Control

2012 IECC and 2015 IECC and 2018 IECC and 2012 IRC and 2015 IRC and 2018 IRC

2012 and 2015 and 2018 IECC R402.4.1/IRC N1102.4.1 Building Thermal Envelope.  Sealing methods used between dissimilar materials should allow for differential expansion and contraction.

IECC R402.4.1.1/IRC N1102.4.1.1 Installation.  The components of the building thermal envelope shall be installed in accordance with manufacturer’s instructions and the criteria indicated in Table R402.4.1.1, as applicable to the method of construction. Where required by the code official, an approved third party shall inspect all components and verify compliance.

IECC Table R402.4.1.1/ IRC Table N1102.4.1.1 Air Barrier and Insulation Installation

General requirements.  A continuous air barrier should be installed in the building envelope (wall).  The exterior thermal envelope contains a continuous air barrier. Breaks or joints in the air barrier should be sealed.  Air-permeable insulation should not be used as a sealing method.

Floors (including above-garage and cantilevered floors). The air barrier shall be installed at any exposed edge of insulation.

Garage separation. Air sealing shall be provided between the garage and conditioned spaces.

2009 IECC and 2009 IRC

2009 IECC R402.4.1/2009 IRC N1102.4.1. Air leakage, Building Thermal Envelope. The building thermal envelope should be durably sealed to limit infiltration. Sealing methods between dissimilar materials should allow for differential expansion and contraction. The following should be caulked, gasketed, weather-stripped, or otherwise sealed with an air-barrier material, suitable film, or solid material:

  • Walls and ceilings separating a garage from conditioned spaces.

2009 IECC R101.4.5. (not in IRC) Change in Space Conditioning.  Any non-conditioned that is altered to become conditioned space must be brought into full compliance with this code. (This means not only the altered assembly must be brought into compliance but the entire space or building would need to be brought into compliance.)

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Case Studies

None Available

References and Resources*

  1. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2009

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  2. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2009

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  3. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2012

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  4. Author(s): ICC
    Organization(s): ICC
    Publication Date: January, 2012

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  5. Author(s): Baechler, Gilbride, Hefty, Cole, Love
    Organization(s): PNNL, ORNL
    Publication Date: February, 2011
    Guide describing measures that builders in the cold and very cold climates can take to build homes that have whole-house energy savings of 40% over the Building America benchmark with no added overall costs for consumers.
  6. Author(s): BSC
    Organization(s): BSC
    Publication Date: September, 2009
    Information sheet about air sealing.
  7. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2017

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

  8. Author(s): Aspen Publishers
    Organization(s): Aspen Publishers
    Publication Date: January, 2000
    Report with information for builders and retrofitters to help eliminate hazards and coincidental energy losses that come from attached garages.
  9. Author(s): Zoeller
    Organization(s): CARB, Steven Winter Associates
    Publication Date: April, 2009

    Information sheet about insulation materials.

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

Last Updated: 12/12/2017