Continuous Air Barrier in Exterior Walls

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Scope

Identify what materials will constitute the continuous air barrier around the building envelope.
Identify what materials will constitute the continuous air barrier around the building envelope.

Ensure that a continuous air barrier exists around the entire thermal envelope of the home and that the air barrier is in full contact with the insulation.

  • Identify on house plans what materials will constitute the air barrier in all components of the home’s thermal envelope including the walls, floors, and ceiling. 
  • Install the continous air barrier which could consist of one or a combination of any of the following air barrier materials: 
    • rigid materials like foam board insulation, drywall, plywood, or OSB
    • flexible materials like house wrap, with all seams and edges sealed and with the house wrap supported using approved fasteners (don't use kraft paper or other materials that tear easily) 
    • fluid-applied membranes like liquid membranes, which are applied with a paint brush, roller, or sprayer over the sheathing
    • spray foam – if used as the air barrier it should be at least 5.5 inches thick if open-cell or at least 1.5 inches thick if closed-cell spray foam insulation.  
  • Seal all seams, gaps, and holes in the air barrier.
  • ENERGY STAR requires that an air barrier be installed at the exterior vertical surface of the wall insulation in all climate zones and also that an air barrier be installed at the interior vertical surface in Climate Zones 4-8.  For ceilings, ENERGY STAR permits the air barrier to be at the interior or exterior horizontal surface in IECC Climate Zones 1-3 and at the interior horizontal surface in Climate Zones 4-8 (ENERGY STAR 2015).

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

The walls, floors, and roof/ceiling compose the physical shell of the home, also called the building enclosure or building envelope. Within these assemblies are components that comprise the home’s thermal envelope (insulation) and air barrier (sometimes referred to as the thermal boundary and pressure boundary). The air barrier layer or layers prevent the unwanted entry of outside air and escape of inside air. Code requires, and best practice dictates, that the home’s thermal layer of insulation be fully aligned with (in full continuous contact with) the home's continuous air barrier (see 2009, 2012, and 2015 IRC). The home’s thermal barrier of insulation must also be continuous for best performance. It should be installed without misalignments, compressions, gaps, or voids. See the guide  Insulation Installation Achieves RESNET Grade 1 for more installing insulation.

The air barrier can consist of any durable solid material that blocks air flow between conditioned space and unconditioned space, for example drywall, OSB, or rigid foam insulation can serve as an air barrier. While ENERGY STAR recommends rigid air barriers, flexible air barriers such as house wrap are acceptable if they are fully sealed at all seams and edges and supported using approved fasteners. For the air barrier to be continuous, any seams between sheets of material, or joints between one material and another, or holes must be sealed with a long-lasting air-sealing material. For example, seams in plywood or OSB can be caulked, seams in rigid foam can be sealed with compatible tapes, joints between drywall and framing can be sealed with caulk or spray foam, gaps around windows can be sealed with foam rods, spray foam, and self adhesive flashing, holes around piping, wiring, or electrical boxes can be sealed with caulk, spray foam, or gaskets. 

The air barrier may be installed on the interior side of the insulation, the exterior side of the insulation, or both, depending on the building component and the climate. For example, according to the ENERGY STAR Rater Field Checklist, in ceilings in IECC Climate Zones 1-3, the air barrier can be aligned with either the interior or exterior horizontal surface of the insulation but, in Climate Zones 4-8, it must be aligned with the interior horizontal surface of the ceilings (i.e., mudded, taped drywall). In walls, the air barrier (e.g., OSB or rigid foam sheathing) should be aligned with the exterior vertical surface of the insulation in all climate zones and also at the interior vertical surface of the wall insulation (the drywall) in Climate Zones 4-8. Regarding floors, the air barrier should be aligned with the exterior vertical surface of the insulation (at the rim joists) in all climate zones and if the floor is over unconditioned space, the subfloor must be aligned with the interior horizontal surface of the floor insulatin (i.e., the insulation must be touching the subfloor above it, for example by installing batt insulation with metal staves or twine that will keep the batts up against the floor above).

While the thermal envelope (the insulation) is easy to see, it is sometimes difficult to determine what components comprise the air barrier, especially where one building component meets another, such as at rim joists. This is a problem because, to be effective, the air barrier must be continuous around the entire building envelope. This can be addressed at the design stage by making a copy of the plans and drawing or highlighting the components that will form the air barrier in each subassembly. See Figure 1.

 

Figure 1. Identify what components comprise the home's air barrier to ensure that the air barrier is consistent around walls, foundation, and ceiling.

 

How to Install a Continuous Air Barrier

  1. Determine the location of the air barrier in the ceilings, walls, and floors, and specify it on the house plans. According to ENERGY STAR requirements, the air barrier location is based on the home’s climate zone location:
    * 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.
    * Walls - At exterior vertical surface of wall insulation in all climate zones; and also at interior vertical surface of wall insulation for Climate Zones 4-8.
    * Floors - At exterior vertical surface of wall insulation in all climate zones; and, if over unconditined space, also at interior horizontal surface with supports to ensure alignment.
  2. Install the air barrier and ensure that is continuous across all components of the thermal envelope (see Figure 2 for an example of continuous air sealing). 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.
    ENERGY STAR Certified Homes recommends, but does not require, rigid air barriers. ENERGY STAR specifices that open-cell foam have a finished thickness ≥ 5.5 inches and closed-cell foam have a finished thickness ≥ 1.5 inches to qualify as an air barrier, unless the manufacturer indicates otherwise. If flexible air barriers such as house wrap are used, they should be fully sealed at all seams and edges and supported using fasteners with caps or heads ≥ 1 inch in diameter, unless otherwise indicated by the manufacturer. Flexible air barriers should not be made of kraft paper, paper-based products, or other materials that are easily torn. If polyethylene is used, its thickness should be ≥ 6 mil. ENERGY STAR highly recommends, but does not require, inclusion of an interior air barrier at band joists in Climate Zone 4 through 8. All insulated vertical surfaces are considered walls (e.g., above- and below-grade exterior walls and knee walls) and must meet the air barrier requirements for walls, with the exception of adiabatic walls in multifamily dwellings. 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.
  3. Air seal all seams, gaps, and holes in the air barrier. For example:
    * Use caulk and approved tape to seal seams in sheathing, subflooring, and drywall.
    * Use caulk and spray foam to seal gaps around wiring, piping, etc.
    * Cut pieces of rigid air blocking material like rigid foam or plywood and caulk in place to block larger air gaps.
    * Use caulk or putty to seal around electrical boxes or install boxes with built-in rubber gaskets.
    * Use sheet metal and fire-rated caulk to air seal around flues.
  4. See the ENERGY STAR Rater Field Checklist, Thermal Enclosure System, 4. Air Sealing, for guides that provide specific air-sealing details. 

 

 

Figure 2 - The air barrier is continuous across several components of the wall, including the foundation, rim joist, bottom plate, wall, window, and header.  Reference

How to Install a Continuous Thermal Barrier

  1. Install the insulation and ensure that it is in full alignment with (in contact with) a continuous air barrier at the walls, floors, and ceilings. Take care to make the air barrier continuous by caulking at joints between wall components such as at rim joists; see Figure 3. Follow RESNET Grade I Insulation Installation Standards when installing the insulation. See the ENERGY STAR Rater Field Checklist, Thermal Enclosure System, 2. Fully-Aligned Air Barriers, for guides that provide specific insulation alignment details. 

  2. Install insulation at levels that meet or exceed code. If pursuing ENERGY STAR certification, insulation levels should meet or exceed the 2009 IECC requirements (Table 402.1.1). If pursuing DOE Zero Energy Ready Home certification, insulation levels should meet or exceed 2012 IECC requirements (Table 402.1.1). See the Compliance tab for additional information.

The wall behind the fireplace is an exterior wall and requires a thermal barrier that is continuous with the rest of the wall’s insulation

Figure 3 - The wall behind the fireplace is an exterior wall and requires a thermal barrier that is continuous with the rest of the wall’s insulation.  Reference

Ensuring Success

Verify with a visual inspection that a continuous air barrier exists to completely enclose the conditioned space of the house. Inspect that all seams, gaps, and holes in the air barrier are sealed with caulk, foam, or tape. Verify whole house air leakage with a blower door test. Visually inspect that all insulation levels meet or exceed 2009 IECC levels and achieve Grade I installation per RESNET standards.

Climate

ENERGY STAR Certified Homes 
ENERGY STAR Certified Homes (Ver. 3/3.1 Ver 08) Rater Field Checklist, A complete air barrier that is fully aligned with insulation is installed at the exterior vertical surface of wall insulation in all climate zones and also at the interior vertical surface of wall insulation in Climate Zones 4-8.
 

DOE Zero Energy Ready Home

DOE Zero Energy Ready Home (Rev 05) Exhibit 2:  Infiltration: Climate Zones 1-2: 3 ACH50; Zones 3-4: 2.5 ACH50; Zones 5-7: 2 ACH50; Zone 8: 1.5 ACH50. Building envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.

 

climate zone map

International Energy Conservation Code (IECC) Climate Regions

Training

Right and Wrong Images

Presentations

None Available

Videos

  1. Other Exterior Walls
    Publication Date: July, 2015
    Courtesy Of: NYSERDA

    Video describing how to properly air seal exterior walls.

CAD Images

Compliance

ENERGY STAR Certified Homes 

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: 

Walls: At exterior vertical surface of wall insulation in all climate zones; also at interior vertical surface of wall insulation in Climate Zones 4-87

2.5 Double-walls and all other exterior walls

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

2.7 All other floors adjoining unconditioned space (e.g., rim / band joists at exterior wall or at porch roof)  

Footnotes:

(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.

(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.

(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.

DOE Zero Energy Ready Home

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. Building envelope assemblies, including exterior walls and unvented attic assemblies (where used), shall comply with the relevant vapor retarder provisions of the 2012 International Residential Code.

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.

2009 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. Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope. The exterior thermal envelope contains a continuous air barrier. Breaks or joints in the air barrier are sealed. 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 and should have an air leakage rate of ≤ 7 at rough-in.

2009 IRC

Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria. Table N1102.4.2, Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope. The exterior thermal envelope contains a continuous air barrier. Breaks or joints in the air barrier are sealed. Air permeable insulation is not used as a sealing material.*

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, Table R402.4.1.1, Air barrier and thermal barrier: A continuous air barrier is installed in the building envelope. The exterior thermal envelope contains a continuous air barrier. 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.

2012 IRC

N1102.4.1.1 Air Barrier and Insulation Installation, 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.*

2015 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, 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 and should have an air leakage rate of ≤ 5 in CZ 1 and 2 or ≤ 3 in CZ 3-8.

2015 IRC

N1102.4.1.1 Air Barrier and Insulation Installation. 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.*

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

More Info.

Contributors to this Guide

The following Building America Teams contributed to the content in this Guide.

Case Studies

  1. Author(s): BSC
    Organization(s): BSC
    Publication Date: July, 2010

    Case study describing project conducted by Habitat for Humanity of Greater Lowell (HfHGL) and Building Science Corporation (BSC).

  2. Author(s): BSC
    Organization(s): BSC
    Publication Date: July, 2012

    Case study of a Concord four-square home retrofitted by Building Science Corporation in Massachusetts.

  3. Author(s): BSC
    Organization(s): BSC
    Publication Date: July, 2010

    Case study of a Concord Cape Cod style home began in August 2008 by architects and engineers at Buliding Science Corporation, who developed the drawing set and specifications for the high performance custom home to be built in Concord, Massachusetts.

  4. Author(s): BSC
    Organization(s): BSC
    Publication Date: July, 2010

    Habitat for Humanity of Greater Lowell bought the land on which to build the Westford House from the town of Westford for $1. Habitat then partnered with Building Science Corporation, the community, local and national manufacturers, distributors and donors in an effort to create a comfortable, healthy, durable and energy efficient single...

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): BSC
    Organization(s): BSC
    Publication Date: May, 2009

    Brochure about creating an air barrier at tub, shower and fireplace walls.

  3. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: February, 2010

    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.

  4. Author(s): Southface Energy Institute, ORNL
    Organization(s): Southface Energy Institute, ORNL
    Publication Date: February, 2000

    Information sheet with information about insulating and ventilating attics.

  5. Author(s): DOE
    Organization(s): DOE
    Publication Date: May, 2015

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

  6. Author(s): EPA
    Organization(s): EPA
    Publication Date: September, 2015

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

  7. Author(s): Georgia Department of Community Affairs
    Organization(s): Georgia Department of Community Affairs
    Publication Date: January, 2011

    Georgia state's minimum standard energy code, including state supplements and amendments.

  8. Author(s): Lstiburek
    Organization(s): BSC
    Publication Date: May, 2009

    Information sheet about air sealing.

  9. 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.

Building Science-to-Sales Translator

Fully Aligned Air Barriers =
Whole-House Draft Barrier

Technical Description: 

A whole-house draft barrier is a continuously connected layer of solid or air-tight materials that block air leaks. This barrier can also function as part of a water barrier, thermal barrier, and vapor barrier, if the location and materials are compatible. For example, rigid foam insulation can provide a combined function. Rigid foam sheets can be used to block air flow when seams are sealed with tape, caulks or adhesives, or liquid applied sealants. An example of an interior air barrier may be the drywall on the home’s walls and ceilings, when the seams are taped and mudded, and caulk, spray foam, or gaskets are used to seal around wiring, plumbing, and other penetrations. Insulation should be in full contact with the air barrier layer.

Alternate Terms

Air Contaminant Barrier
Energy Saving Air Barrier
Advanced Air Barrier Technology
Professionally-Installed Draft Barrier
Moisture Control Air Barrier
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?
Last Updated: 03/14/2016

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