Batt Insulation for Existing Exterior Walls

Scope Images
Unfaced fiberglass batt insulation is installed to completely fill the wall cavities and is sliced to fit around wiring, piping, and other obstructions in the wall cavities
Unfaced fiberglass batt insulation is installed to completely fill the wall cavities and is sliced to fit around wiring, piping, and other obstructions in the wall cavities
Scope

If installing batts in the walls of an existing home, meet RESNET Grade 1 quality installation standards and meet or exceed code for the insulation level R-value requirement.

Unfaced fiberglass batt insulation is properly installed to completely fill the wall cavities and is sliced to fit around wiring, piping and other obstructions.

See the U.S. Department of Energy Standard Work Specifications for additional guidance on installing batt insulation in walls.

For guidance on working in walls, see the Pre-Retrofit Assessment of Walls, Windows, and Doors.

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

Fiberglass or mineral wool batt insulation is not likely to be installed as an upgrade to an existing home, unless an addition is being added or perhaps in the case of a gut rehab where drywall is removed and replaced. If batt insulation will be installed, install the insulation in a manner that meets the Grade 1 standards of the Residential Energy Services Network (RESNET) in its Home Energy Rating System Standards (RESNET 2013). Grade 1 Installation requires that insulation material should uniformly fill wall cavities, filling each cavity from side to side and top to bottom, without substantial gaps or voids (Figure 1). The batt insulation should be cut to fit around any wiring or piping installed in the wall cavities (Figure 2). For more information, see the Building America Solution Center guide, Insulation Installation Achieves RESNET Grade 1.

Showing cutting methods of batt insulation

Figure 1. Batt insulation should be cut to fit around wiring or pipes in walls cavities (Source).

Correctly installed fiberglass batt

Figure 2. This fiberglass batt is incorrectly installed; the batts should be sliced to fit around wiring (Source).

There are many factors to consider when installing batt insulation from either the interior or exterior. Understanding Vapor Barriers is a good primer on what needs to be considered regarding vapor retarders.

There are other insulation materials that might be considered for retrofit applications where the drywall will not be removed. These could include blown fiberglass or cellulose that is installed from the exterior of the wall using the “drill and fill” method as described in the guide Blown Insulation for Cavities of Existing Exterior Walls, or rigid foam, also typically installed on the exterior, which might be chosen as part of a home re-siding project as described in the guide Rigid Foam Insulation for Existing Exterior Walls. Spray foam might be considered for existing walls where either drywall or exterior cladding and sheathing will be removed. Each of these methods has its own advantages and disadvantages; see the referenced guides for more information when selecting a retrofit approach.

How to Install Batt Insulation in Walls in Existing Homes

  1. Consider the scope and goals of the project to determine the best insulation product for the job.
  2. If using batt insulation, select the appropriate size for your wall cavities and the right R-value for your project.
  3. Remove drywall and any old insulation from wall cavities.
  4. Air seal any gaps around penetrations and any seams in sheathing.
  5. Install batts in accordance with the RESNET Grade 1 standard: the batt insulation should uniformly fill the wall cavities, filling each cavity from side to side and top to bottom, without substantial gaps or voids (Figure 1).
  6. Cut or slice batt insulation to fit around any wiring or piping installed in the wall cavities (Figure 2).
  7. Install, mud, and tape new drywall. 
Ensuring Success

Visually inspect the batt installation to verify that the installation meets RESNET Grade 1 quality standards.

Climate

The exterior wall assembly should be designed for a specific hygrothermal region, rain exposure zone, and interior climate.  The climate zones are shown on the map below, which is taken from Figure C301.1 of the 2012 IECC.

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. 

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

The insulation levels should be based on the minimum requirements for vapor control in the current adopted building code and the minimum requirements for thermal control in the current energy code.  Additional insulation can be added above these minimums to create high R-Value exterior wall assemblies. The table below provides the minimum thermal resistance (R-value) requirements for exterior walls specified in the 2009 IECC (ICC 2009b) and the 2012 IECC (ICC 2012b), based on climate zone.

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

Table 1. Wall Insulation Requirements per the 2009 and 2012 IECC (same for 2015 and 2018 IECC).

Videos
Author(s)
Advanced Energy
Organization(s)
Advanced Energy
Description
Brian Coble, Director of High Performance Homes for Advanced Energy provides best practices on "Proper Installation of Insulation" as he walks viewers through an ENERGY STAR Home and points out every area of a home that must be insulated to meet RESNET Grade 1 Insulation Installation Requirements...
Publication Date
Author(s)
Advanced Energy
Organization(s)
Advanced Energy
Description
Brian Coble, Director of High Performance Homes for Advanced Energy provides best practices on "Proper Installation of Insulation" as he walks viewers through an ENERGY STAR Home and points out every area of a home that must be insulated to meet RESNET Grade 1 Insulation Installation Requirements...
Publication Date
Author(s)
Advanced Energy
Organization(s)
Advanced Energy
Description
Brian Coble, Director of High Performance Homes for Advanced Energy provides best practices on "Proper Installation of Insulation" as he walks viewers through an ENERGY STAR Home and points out every area of a home that must be insulated to meet RESNET Grade 1 Insulation Installation Requirements...
CAD

Compliance

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

ENERGY STAR Certified Homes, Version 3/3.1 (Rev. 09)

National Rater Field Checklist

Thermal Enclosure System.
2. Fully-Aligned Air Barriers.6 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 4-8.8

Footnote 6) 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, paperbased products, or other materials that are easily torn. If polyethylene is used, its thickness shall be ≥ 6 mil.

Footnote 8) 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.

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) 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 12) Building envelope assemblies, including exterior walls and unvented attic assemblies (where used), shall comply with the relevant vapor retarder provisions of the 2015 International Residential Code (IRC).
Footnote 23) Envelope leakage shall be determined by an approved verifier using a RESNET-approved testing protocol.

American Society for Testing Materials (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, 2012, 2015, 2018, and 2021 International Energy Conservation Code (IECC) and International Residential Code (IRC) Minimum Insulation Requirements: 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 IECC

Table 402.4.2 Air Barrier and Insulation Inspection Component Criteria, 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

Exterior insulation for framed walls is in substantial contact and continuous alignment with the air barrier. Table R402.4.1.1 Air Barrier and Insulation Installation, 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 and 2018 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. Walls: Insulation in exterior framed walls is in substantial contact and continuous alignment with the air barrier. 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 ASTM E 1827 (or RESNET/ICC 380 in 2018 IECC) 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 (Section R501.1.1 in 2015, 2018, and 2021 IECC). 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.)

2009 IRC 

Table N1102.4.2 Air Barrier and Insulation Inspection Component Criteria, 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 IRC

Exterior insulation for framed walls is in substantial contact and continuous alignment with the air barrier. Table N1102.4.1.1 Air Barrier and Insulation Installation, 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 IRC and 2018 IRC

N1102.4.1.1 Air Barrier and Insulation Installation. Walls: Insulation in exterior framed walls is in substantial contact and continuous alignment with the air barrier. 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, 20152018, and 2021 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018, N1109.1 in 2021 IRC). 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.)

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

NFPA 70: National Electrical Code

Article 394.1: If a home has knob and tub wiring, insulation should not be applied to touch or surround the wiring. 

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.

References and Resources*
Author(s)
Cottrell
Organization(s)
RESNET,
North American Insulation Manufacturers Association
Publication Date
Description
Presentation describing RESNET grading criteria for insulation installation.
*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.

Pacific Northwest National Laboratory

Building Science Measures
Building Science-to-Sales Translator

High-R Wall Insulation = High-Efficiency or Ultra-Efficient Wall Insulation

Image(s)
Technical Description

There are two levels of wall insulation: high-efficiency insulation, which meets the 2015 International Energy Conservation Code, and ultra-efficient insulation, which is 25% more efficient than this national code. Using high-efficiency and ultra-efficient insulation along with professional installation (e.g., no gaps, voids, compression, or misalignment with air barriers, complete air barriers, and minimal thermal bridging) creates conditioned spaces that require very little heating and cooling, along with even comfort and quiet throughout the house.

High-Efficiency or Ultra-Efficient Wall Insulation
Sales Message

High-efficiency wall insulation helps provide added thermal protection. What this means to you is less wasted energy along with enhanced comfort and quiet. Knowing there is one opportunity to optimize performance during construction, wouldn’t you agree it’s a great opportunity to meet or exceed future codes?

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