Air Sealing and Insulating Ceilings

    Scope Images
    Image
    Install a continuous air barrier below or above ceiling insulation and install wind baffles.
    Scope

    Install a continuous air barrier that is fully aligned with (touching) the ceiling insulation.

    • The air barrier could consist of drywall that is taped and sealed at seams, or another durable, solid surface like plywood or OSB, or house wrap that is sealed at the seams. Kraft-paper, paper products, or other materials that tear easily should not be used.
    • If spray foam insulation is used, 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.  
    • Install an air barrier that is continuous and in full contact with the insulation.
    • ENERGY STAR specifies that the air barrier be installed at either the interior or exterior surface of the ceiling insulation in Climate Zones 1-3; or at the interior surface of the ceiling insulation in IECC Climate Zones 4-8 (ENERGY STAR). 
    • Install an air barrier at the vertical edges of the insulation at the attic eaves in all climate zones using a wind baffle that extends to the full height of the insulation in every rafter bay or a tabbed baffle in each bay with a soffit vent. The baffle will also prevent wind from washing through the insulation in adjacent bays. Install wind baffles with the minimum code required clearance between the baffle and the roof deck.

    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 Single-Family New Homes, and Indoor airPLUS.

    Description

    In simplest terms, a house is a six-sided assembly composed of four walls, a roof, and a floor. When these components are all connected, they comprise the building enclosure or the physical shell of the home. Within these assemblies are components that comprise the home’s thermal envelope (insulation) and air barrier. For the best performance, the home’s thermal layer should be fully aligned with (in full continuous contact with) the air barrier.

    In a home with a vented attic, the ceiling provides the air barrier. The ceiling air barrier, which usually consists of taped, mudded drywall, should be continuous and all holes through it for wiring, electrical boxes, light fixtures, flue and chimney pipes, duct chases, heating registers, soffits, etc., should be thoroughly air sealed before insulation is installed. See the ENERGY STAR Rater Field Checklist in the Building America Solution Center and the guides attached to Section 2 "Fully Aligned Air Barriers" and Section 4 "Air Sealing" for instructions on specific air-sealing measures. For more on air sealing the top plates to the ceiling drywall to provide a continuous ceiling air barrier, see the guide Air Sealing Drywall to Top Plates.

    To help maintain consistent insulation over this ceiling air barrier, wind dams and baffles should be installed in the attic in every rafter bay that has a soffit vent. A wind dam (called a soffit dam in Figures 3 and 4 below) consists of a piece of rigid material (rigid foam, OSB, plywood, etc., that is installed vertically just outside of the top plate and extending up to the baffle to direct ventilation air up from the soffit vent to the underside of the roof. It prevents wind that enters the soffit vent from pushing insulation away from the eaves and it also provide a "backstop" when insulation is installed to keep it from falling through the soffit vent. In some cases the exterior wall sheathing extends up to provide the wind dam (see Figure 1). Baffles are 2-inch-deep chutes made of plastic, cardboard, or metal, 2 to 4 feet in length, and in widths to fit in 16-inch on-center or 24-inch on-center rafter bays. They can be connected to the wind dam or they often come with a flat tab at the end that can be bent down to serve as the wind dam. The baffle maintains a 2-inch air gap between the underside of the roof deck and the insulation to guide air from the soffit vents up along the underside of the roof to ridge vents. The baffles also help to protect the insulation from wind washing.

    It is important to maintain a minimum amount of insulation, preferably equivalent to the insulation depth of the rest of the attic, over the top plates of the exterior walls. This will prevent cold spots along the exterior walls and ensure a consistent R-value across the ceiling. Building the roof with raised heel “energy” trusses (as shown in Figures 1, 3, and 4) will allow the full height of insulation to be installed over the top plates. See Attic Eave Minimum Insulation for more information.

    After all holes through the ceiling are air sealed and the baffles have been installed, the insulation can be installed in full contact with the ceiling drywall, which is the air barrier.
    Figure 1. After all holes through the ceiling are air sealed and the baffles have been installed, the insulation can be installed in full contact with the ceiling drywall, which is the air barrier.

     

    Baffles can be made of plastic, metal, cardboard, or molded rigid foam. The baffles provide an air space over the insulation to guide ventilation air from the soffit vents up along the underside of the roof deck.
    Figure 2. Baffles can be made of plastic, metal, cardboard, or molded rigid foam. The baffles provide an air space over the insulation to guide ventilation air from the soffit vents up along the underside of the roof deck.

     

    How to Air Seal and Insulate the Ceiling

    1. Design the home with raised heel energy trusses ( if you are using trusses) or roof rafters with a raised top plate (if you are building the rafters on site).
      Raised heel, energy trusses extend further past the wall and are deeper at the wall allowing room for full insulation coverage over the top plate of the exterior walls.
      Figure 3. Raised heel energy trusses extend further past the wall and are deeper at the wall allowing room for full insulation coverage over the top plate of the exterior walls.
      A site-built rafter roof with a raised top plate allows for more insulation underneath.
      Figure 4. A site-built rafter roof with a raised top plate allows for more insulation underneath.
    2. Thoroughly air seal all holes through the ceiling.
    3. Install baffles in each rafter bay that has a vent. Choose and install the baffles correctly to provide the code-required minimum air space between the baffle and the roof deck.
      The soffit dam and baffle allow air to flow through the vents without disturbing the insulation covering the top plates.
      Figure 5. The soffit dam and baffle allow air to flow through the vents without disturbing the insulation covering the top plates.
    4. Cover the ceiling deck with blown, batt, or spray foam insulation to the full height required to meet or exceed the minimum value for the climate zone. ENERGY STAR requires that all insulated ceiling surfaces meet the requirements for ceilings, regardless of slope (e.g., cathedral ceilings, tray ceilings, conditioned attic roof decks, flat ceilings, sloped ceilings).
    Ensuring Success

    Verify with a visual inspection that a continuous air barrier exists at the interior surface of ceilings in Climate Zones 4-8 and at the interior or exterior surface of ceilings in Climate Zones 1-3. This air barrier should be fully aligned with the insulation across the entire surface of the ceiling including at the eaves. Verify that wind dams and baffles are installed in every bay with a soffit vent to prevent wind washing. Measure baffles to confirm that the baffles meet the minimum code-required clearance between the baffle and the roof deck. 

    Climate

    The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide. 

    Climate Zone Map from IECC 2009, 12, 15, and 18.
    Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18. (Source: 2012 IECC)

     

    Climate Zone Map from IECC 2021.
    Figure 2. Climate Zone Map from IECC 2021. (Source: 2021 IECC)

     

    Right and Wrong Images
    Image
    Wrong – Wind baffle installation will not allow insulation over the top plate
    Wrong – Wind baffle installation will not allow insulation over the top plate
    Image
    Right – Wind baffle installation will allow proper insulation depth over the top plate
    Right – Wind baffle installation will allow proper insulation depth over the top plate
    Image
    Right – Wind baffle installation maintains necessary code clearance between baffle and roof deck
    Right – Wind baffle installation maintains necessary code clearance between baffle and roof deck
    Image
    Wrong – Ceiling insulation not completely installed/air barrier missing
    Wrong – Ceiling insulation not completely installed/air barrier missing
    Image
    Right - a dropped ceiling below a taped plywood air barrier provides a service cavity for ducts and wiring.
    Right - a dropped ceiling below a taped plywood air barrier provides a service cavity for ducts and wiring.
    Image
    Right – Open-cell spray foam fills the walls and cathedral ceilings of this multi-story home.
    Right – Open-cell spray foam fills the walls and cathedral ceilings of this multi-story home.
    Image
    Right - The ceiling joists of the cathedral ceilings in this dry-climate home are filled with fiberglass batt insulation.
    Right - The ceiling joists of the cathedral ceilings in this dry-climate home are filled with fiberglass batt insulation.
    Image
    Right – Spray foam fills the cathedral ceilings of the home.
    Right – Spray foam fills the cathedral ceilings of the home.
    Image
    The polyethylene ceiling vapor barrier is sealed to form an air barrier around the exhaust fan in this very cold climate location (≥ CZ 6).
    The polyethylene ceiling vapor barrier is sealed to form an air barrier around the exhaust fan in this very cold climate location (≥ CZ 6).
    Image
    Garage ceiling with spray foam flash air seal plus batt insulation
    Garage ceiling with spray foam flash air seal plus batt insulation
    Image
    Blown cellulose insulation completely fills the netted wall and ceiling cavities
    Blown cellulose insulation completely fills the netted wall and ceiling cavities
    Image
    The ceiling over an unconditioned space is insulated with closed-cell spray foam that fills the ceiling cavities and encapsulates the framing
    The ceiling over an unconditioned space is insulated with closed-cell spray foam that fills the ceiling cavities and encapsulates the framing
    Image
    Rigid foam insulating sheathing installed over an existing garage ceiling with retrofits to air seal exterior wall before adding exterior wall insulating sheathing
    Rigid foam insulating sheathing installed over an existing garage ceiling with retrofits to air seal exterior wall before adding exterior wall insulating sheathing
    Image
    Right – Open-cell spray foam fills the walls and cathedral ceilings of this multi-story home.
    Right – Open-cell spray foam fills the walls and cathedral ceilings of this multi-story home.
    Image
    Right – A bead of sealant will form an airtight gasket between the top plate and drywall.
    Right – A bead of sealant will form an airtight gasket between the top plate and drywall.
    Image
    Right - The ceiling joists of the cathedral ceilings in this dry-climate home are filled with fiberglass batt insulation.
    Right - The ceiling joists of the cathedral ceilings in this dry-climate home are filled with fiberglass batt insulation.
    Image
    Right – Spray foam fills the cathedral ceilings of the home.
    Right – Spray foam fills the cathedral ceilings of the home.
    Image
    Right – This roof consists of parallel truss chords which allows for cathedral ceilings.
    Right – This roof consists of parallel truss chords which allows for cathedral ceilings.
    Image
    Spray foam insulates and air seals the ceiling deck and top plates of this vented attic.
    Spray foam insulates and air seals the ceiling deck and top plates of this vented attic.
    Image
    Insulation was added to the walls and ceiling of this existing home from the inside as part of an extensive retrofit to avoid replacing original 1-inch shiplapped sheathing.
    Insulation was added to the walls and ceiling of this existing home from the inside as part of an extensive retrofit to avoid replacing original 1-inch shiplapped sheathing.
    Image
    Wrong - IR image shows a lack of air sealing and insulation around a ceiling light fixture.
    Wrong - IR image shows a lack of air sealing and insulation around a ceiling light fixture.
    Image
    Wrong - IR image is showing that attic access is missing weather stripping.
    Wrong - IR image is showing that attic access is missing weather stripping.
    Image
    Wrong - Ceiling HVAC register is improperly installed on an angled ceiling.
    Wrong - Ceiling HVAC register is improperly installed on an angled ceiling.
    Image
    Wrong - Batt insulation is poorly installed leaving gaps along the ceiling.
    Wrong - Batt insulation is poorly installed leaving gaps along the ceiling.
    Videos
    CAD
    CAD Files
    Conceptual insulation practice at attic-style truss system - above unconditioned space
    Conceptual insulation practice at attic-style truss system - above unconditioned space
    Download: DWG PDF
    Conceptual insulation practice at attic-style truss system - above conditioned space
    Conceptual insulation practice at attic-style truss system - above conditioned space
    Download: DWG PDF

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)

    National Rater Field Checklist

    Thermal Enclosure System.
    2. Fully-Aligned Air Barriers.7 At each insulated location below, a complete air barrier is provided that is fully aligned as follows:
    Ceilings: At interior or exterior horizontal surface of ceiling insulation in Climate Zones 1-3; at interior horizontal surface of ceiling insulation in Climate Zones 4-8. Also, at exterior vertical surface of ceiling insulation in all climate zones (e.g., using a wind baffle that extends to the full height of the insulation in every bay or a tabbed baffle in each bay with a soffit vent that prevents wind washing in adjacent bays).8​
    2.1 Dropped ceilings / soffits below unconditioned attics, and all other ceilings.

    3. Reduced Thermal Bridging.
    3.1 For insulated ceilings with attic space above (i.e., non-cathedralized), Grade I insulation extends to the inside face of the exterior wall below and is ≥ R-21 in CZ 1-5; ≥ R-30 in CZ 6-8.14

    Footnote 7) 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.

    Footnote 8) 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.

    Footnote 14) The minimum designated R-values must be achieved regardless of the trade-offs determined using an equivalent U-factor or UA alternative calculation. Note that if the minimum designated values are used, then higher insulation values may be needed elsewhere to meet Item 1.2. Also, note that these requirements can be met by using any available strategy, such as a raised-heel truss, alternate framing that provides adequate space, and / or high-density insulation.

    Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program. 
    Exhibit 1, Item 2) Ceiling, wall, floor, and slab insulation shall meet or exceed 2015 IECC levels and achieve Grade 1 installation, per RESNET standards. See the guide 2015 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

    Exhibit 2 DOE Zero Energy Ready Home Target Home.
    The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements (Rev 07), as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.

    Exhibit 2, Insulation and Infiltration) Insulation levels shall meet the 2015 IECC and achieve Grade 1 installation, per RESNET standards.
     Whole house leakage must be tested and meet the following infiltration limits:

    • Zones 1-2: ≤ 3 ACH50;
    • Zones 3-4: ≤ 2.5 ACH50;
    • Zones 5-7: ≤ 2 ACH50;
    • Zone 8: ≤ 1.5 ACH50;
    • Attached dwellings: ≤ 3 ACH50.

    Footnote 9) With respect to Provision 1.3 within the ENERGY STAR Qualified Homes, Version 3/3.1 (REV09) Rater Field Checklist requiring RESNET-defined Grade I installation of insulation, where ceiling, wall, or floor assembly insulation is installed "blind" between layers of sheathing and therefore cannot be visually inspected, such assemblies are deemed equivalent to a RESNET-defined Grade I installation if the assembly insulation level is at least 50% greater than the specified value for the DOE Zero Energy Ready Home Target Home, based on nominal R-value.

    Footnote 13) Insulation levels in a home shall meet or exceed the component insulation requirements in the 2015 International Energy Conservation Code (IECC) – Table R402.1.2. The following exceptions apply:

    a. Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 2015 IECC – Table 402.2.6.

    b. For ceilings with attic spaces, R-30 shall satisfy the requirement for R-38 and R-38 shall satisfy the requirement for R-49 wherever the full height of uncompressed insulation at the lower R-value extends over the wall top plate at the eaves. This exemption shall not apply if the alternative calculations in d) are used;

    c. For ceilings without attic spaces, R-30 shall satisfy the requirement for any required value above R-30 if the design of the roof / ceiling assembly does not provide sufficient space for the required insulation value. This exemption shall be limited to 500 sq. ft. or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in d) are used;

    d. An alternative equivalent U-factor or total UA calculation may also be used to demonstrate compliance, as follows: An assembly with a U-factor equal to or less than specified in Table 402.1.4 of the 2015 IECC complies. A total building thermal envelope UA that is less than or equal to the total UA resulting from the U-factors in Table 402.1.4 also complies. The insulation levels of fenestration, ceilings, walls, floors, and slabs can be traded off using the UA approach under both the Prescriptive and the Performance Path. Also, note that while ceiling and slab insulation can be included in trade-off calculations, Items 3.1 through 3.3 of the ENERGY STAR Rev09 Rater Field Checklist shall be met regardless of the UA tradeoffs calculated. The UA calculation shall be done using a method consistent with the ASHRAE Handbook of Fundamentals and shall include the thermal bridging effects of framing materials. The calculation for a steel-frame envelope assembly shall use the ASHRAE zone method or a method providing equivalent results, and not a series-parallel path calculation method.

    Footnote 23) Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.

     

    2009-2021 IECC and IRC Insulation Requirements Table

    The minimum insulation requirements for ceilings, walls, floors, and foundations in new homes, as listed in the 2009, 2012, 2015, 2018, and 2021 IECC and IRC, can be found in this table

     

    2009 International Energy Conservation Code (IECC)

    Table R402.1.1 Insulation and Fenestration Requirements – meet or exceed the insulation levels listed in this table.

    Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria,  Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. Table 402.4.2, Air barrier and thermal barrier: Air permeable insulation is not used as a sealing material.

    Section R402.4.2 Air sealing and insulation is demonstrated by testing or visual inspection. Testing.  The building should be tested for air leakage should have an air leakage rate of ≤ 7 at rough-in.

    2012 IECC

    Table R402.1.1 Insulation and Fenestration Requirements – meet or exceed the insulation levels listed in this table.

    Table R402.4.1.1 Air Barrier and Insulation Installation, Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. 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.

    Section R402.4.1.2 Testing.  The building should be tested for air leakage and should have an air leakage rate of ≤ 5 in CZ 1 and 2 or ≤ 3 in CZ 3-8.

    20152018, and 2021 IECC

    Table R402.1.2 Insulation and Fenestration Requirements – meet or exceed the insulation levels listed in this table.

    Table R402.4.1.1 Air Barrier and Insulation Installation, Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. General requirements: A continuous air barrier is installed in the building envelope; breaks and joints in the air barrier are sealed. Air-permeable insulation is not used as an air-sealing material.

    Section R402.4.1.2 Testing.  The building should be tested for air leakage in accordance with ASTM E 779 or E 1827 (or RESNET/ICC 380 in IECC 2018/2021)  and should have an air leakage rate of ≤ 5 in CZ 1 and 2 or ≤ 3 in CZ 3-8.

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

    Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

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

     

    2009 International Residential Code (IRC)

    Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria,  Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. Table N1102.4.2, Air barrier and thermal barrier: Air permeable insulation is not used as a sealing material.

    2012 IRC

    N1102.4.1.1 Air Barrier and Insulation Installation, Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. 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.

    20152018, and 2021 IRC

    N1102.4.1.1 Air Barrier and Insulation Installation, Ceiling/attic: Air barrier in any dropped ceiling/soffit is substantially aligned with insulation and any gaps are sealed. General requirements: A continuous air barrier is installed in the building envelope; breaks and joints in the air barrier are sealed. Air-permeable insulation is not used as an air-sealing material.

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

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

    Existing Homes

    SCOPE

    Retrofit an existing ceiling to establish a complete thermal barrier by air sealing and insulating.

    • Air seal the top plates and all penetrations through the ceiling, including the attic hatch and pull-down stair openings, chimneys, bathroom fans, recessed ceiling lights, electrical boxes, and plumbing stacks.
    • Inspect attic eaves and soffit vents. Set aside existing insulation. Re-install any missing vent grating. Replace missing baffles and wind dams. Caulk top plate-to-drywall junctures, if accessible. Install insulation to full available height over top plates.
    • See the Scope and Description tabs for additional guidance.

    For more information on conditions that may be encountered when working in attics in existing homes, see the assessment guides on attics and hazardous materials.  

    See the U.S. Department of Energy’s Standard Work Specifications for more on air sealing and working in attics. Follow safe work practices as described in the Standard Work Specifications.

    DESCRIPTION

    Adding attic insulation is a popular retrofit in older homes. However, before adding insulation it’s important to make sure that the ceiling deck (attic floor) is well air sealed. The porous blown or batt insulation typically used will do little to stop the movement of conditioned air out of the home and into the attic if there are gaps around light fixtures, flues, dry wall-to-top plate junctures, etc. In a home with a vented attic, the properly air-sealed ceiling with attic insulation on top serves as an important part of the home’s thermal envelope. See the Description tab for more on this concept.  For the best performance, the home’s thermal layer should be fully aligned with (in full continuous contact with) the air barrier and the air barrier should be continuous with no air leaks.

    Specific attic air sealing measures are described in several Building America Solution Center guides, as well as in the Measure Guideline: Guide to Attic Air Sealing by Building Science Corporation. Note that locating penetrations underneath attic insulation is often challenging, and may require such steps as tracing wiring and measuring from base points visible from both the interior of the house and the interior of the attic.  Note also that not all penetrations may be accessible for sealing (for example, those located at the perimeter of the attic where there is minimal head clearance). Sealing large and accessible holes will improve energy efficiency and comfort, even if the work cannot be performed perfectly at every single penetration.

    Insulation should completely cover the attic floor and the insulation depth across the attic ceiling should be consistent. See the Description tab for a description of baffles and wind dams, which help to keep insulation from getting blown away from soffit vents while maintaining a ventilation gap from soffit vents to ridge vents.

    Note that, although the purpose of air sealing is to improve energy efficiency and comfort, it is important not to compromise health, safety, and durability in the process. Combustion safety, ventilation for indoor air quality, durability, and attic ventilation should be addressed first, before performing attic air sealing. This work will be performed inside the attic so use safe work practices and be aware of hazardous conditions as described in the attic assessment guide.

    How to Insulate and Air Seal an Existing Attic to Establish a Consistent Thermal Boundary

    1. Inspect the house, checking for combustion appliances, controlled ventilation, and required attic ventilation.

    Do not proceed if:

    • The house attic has active knob and tube wiring.
    • The house attic has vermiculite insulation.
    • The house attic has bathroom fans vented into the attic.
    • The house has a leaking roof.
    • The house has an unvented kerosene heater or gas fireplace.
    1. Ensure combustion safety. If there is a natural draft (Category 1) gas- or oil-fired furnace or a gas- or oil-fired water heater or boiler located in the home, see the Assess Combustion Safety guide for more information including testing requirements. Consider replacing the natural draft appliances with a sealed combustion, induced draft, or power-vented appliance. Install carbon monoxide detectors.
    2. Ensure ventilation for indoor air quality. Air sealing will reduce the amount of air that will enter the home through uncontrolled means. Controlled ventilation is required. See the guide Whole-Building Delivered Ventilation.
    3. Ensure Attic Ventilation. All roofs must be vented according to the applicable building code. Most residential roofs are vented with soffit vents, but ridge vents, mushroom cap vents, and gable vents are also common. The size and location of the vents should be determined by referencing the applicable building code. (See Lstiburek 2014.)
    4. Identify areas to be air sealed. This includes all penetrations through the ceiling, including the chimneys, flues, bathroom fans, electrical boxes, and plumbing stacks,  recessed ceiling lights, attic hatch and pull-down stair openings, as well as top plates for all exterior and interior walls. The contractor may want to start with a walk-through of the home, noting potential sources of leaks on a sketch of the home.
    5. Move existing insulation away from penetrations and brush away dust and debris.
    6. Air seal gaps, seams, and holes using caulk and spray foam sealants. Rigid board material such as plywood, OSB, drywall, or rigid foam board can be sealed into place to seal larger gaps. See specific guides for more on sealing electrical, plumbing, and flues and penetrations with complicated interfaces such as recessed ceiling lightsdropped soffitsattic hatch and pull-down stair openings, as well as top plates for all exterior and interior walls.
    7. Replace insulation and add insulation to compensate for insulation compressed during air sealing activities.
    8. Inspect attic eaves and soffit vents. Set aside existing insulation. Re-install any missing vent grating. Replace missing baffles and wind dams. Caulk top plate-to-drywall junctures, if accessible.
    9. Replace insulation and add insulation to full available height over top plates.
    10. Add insulation to desired depth across the entire attic.

    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
    Author(s)
    Pacific Northwest National Laboratory,
    U.S. Department of Energy
    Organization(s)
    PNNL,
    DOE
    Publication Date
    Description
    Case study describing a 4,763 ft2 certified Passive House that achieved HERS 27 without PV through the construction of R-54 walls that use ICF plus fiberglass cavity insulation, an R-100 vented attic, extensive air sealing and flashing, triple-pane windows, ductless heat pumps, and solar hot water.
    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)
    Southface Energy Institute,
    Oak Ridge National Laboratory
    Organization(s)
    Southface Energy Institute,
    ORNL
    Publication Date
    Description
    Information sheet with information about insulating and ventilating attics.
    Author(s)
    Lstiburek
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Document providing background and approach for the prep work necessary prior to adding attic insulation - focusing on combustion safety, ventilation for indoor air quality, and attic ventilation for durability.
    Author(s)
    Lstiburek
    Organization(s)
    Building Science Corporation
    Publication Date
    Description
    Report that provides information and specifications to anyone that is attempting to air seal existing attics.
    *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.

    Building Science Measures
    Building Science-to-Sales Translator

    Fully Aligned Air Barriers = Whole-House Draft Barrier

    Image(s)
    Technical Description

    A whole-house draft barrier is a continuous layer of air-tight materials that block air leaks. This barrier can be integrated with other materials to also function as a water barrier, thermal barrier, and vapor barrier. For example, rigid foam insulation can be used to block thermal flow as well as air flow when seams are sealed with tape, caulk, adhesives, or liquid-applied sealants. Some rigid foams have an integrated water control layer as well. Additionally, drywall can serve as an interior air barrier when the seams are taped and spackled, and caulk, spray foam, or gaskets are used to seal around wiring, plumbing, and other penetrations. It also serves as the vapor barrier when finished with paint. Insulation should be in full contact with the air barrier layer.

    Whole-House Draft Barrier
    Sales Message

    Whole-house draft barriers block air flow that can undermine the thermal protection with a complete high-performance insulation system. What this means to you is less wasted energy along with enhanced comfort, 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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