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Attic Eave Minimum Insulation

    Scope
    Scope Images
    Image
    Design the roof with raised heel trusses to allow full insulation over the top plates of the exterior walls.
    Scope

    Design the roof framing to allow full insulation over the top plates of the exterior walls.

    • Install raised heel trusses or use another roof framing method that allows space to install insulation over the top plates of the exterior walls, or install high-R-value insulation, to achieve an R-value that approaches code minimums for attic insulation.
    • ENERGY STAR requires ≥ R-21 in climates zones 1 through 5 and ≥ R-30 in climates zones 6-8. The insulation must extend over the top plate of the exterior wall and be installed using RESNET Grade 1 insulation techniques (ENERGY STAR).

    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
    Description

    In vented attics, insulation is laid on the ceiling deck of the top floor of the home. Maintaining the insulation level throughout the entire plane of the ceiling and over the top of the perimeter walls is key to preventing heat flow through the ceiling and into or out of the home. When the roof pitch is low at the eaves, insulation may be compressed or lacking. In the winter in cold climates this can cause cold spots along ceilings and subsequent condensation concerns, while also causing warm spots at the roof deck which can cause snow melt and therefore contribute to ice dam formation in snowy climates. This can be true of roofs built with pre-made trusses and roof rafters constructed on site.

    Standard roof trusses are narrow at the eaves, preventing full insulation coverage over the top plate of the exterior walls.
    Figure 1. Standard roof trusses are narrow at the eaves, preventing full insulation coverage over the top plate of the exterior walls (Source: Georgia State Supplements and Amendments to the International Energy Conservation Code 2011). 

     

    A standard site-built roof of rafters may pinch the insulation at the eaves.
    Figure 2. Standard site-built roof rafters may pinch the insulation at the eave (Source: Georgia State Supplements and Amendments to the International Energy Conservation Code 2011). 

     

    Builders and architects have several options for designing pitched, vented roofs that allow the insulation to achieve its full thickness over the plate line of the exterior walls: elevating the heel (sometimes referred to as an energy truss, raised-heel truss, or Arkansas truss), use of cantilevered or oversized trusses, lowering the ceiling joists, or framing with a raised rafter plate (BECP 2011). For a truss roof, raised heel energy trusses or oversized (cantilevered) trusses that form elevated overhangs, in combination with rafter baffles and soffit dams, will provide clearance for both full-height insulation and ventilation.

    In stick-built roofs where rafters and ceiling joists are cut and installed at the construction site, laying an additional top plate across the top of the ceiling joists at the eave will raise the roof height, prevent compression of the attic insulation, and permit ventilation. When installing a raised top plate, place a band joist at the open joist cavities of the roof framing. The band joist also serves as a soffit dam, helping to prevent wind washing of the attic insulation (where air entering the soffit vents flows through the attic insulation, which can reduce attic insulation R-values on extremely cold days or add moisture to the insulation) (Southface and ORNL 2000Straube and Grin 2010).

    With a cathedral ceiling, a vaulted parallel chord truss roof can be constructed. Cathedral ceilings must provide space between the roof deck and ceiling for adequate insulation and ventilation. The 2009 IECC requires at least R-30 in areas where the roof-ceiling design doesn’t allow for more. Insulation levels of R-30 or higher can be achieved through the use of truss joists, scissor truss framing, or sufficiently large rafters. For example, cathedral ceilings built with 2x12 rafters have space for standard 10-inch, R-30 batts and ventilation.

    The designer should specify energy trusses or other constructions that will allow full height construction and baffles on building plans. These designs will be implemented by the framer. The insulation contractor should install the insulation correctly to full depth and install rulers. This task should be included in the contract for the appropriate trade, depending on the workflow at a specific job site.

    If the roof is designed with limited height over the exterior top plates, an option is to install higher R-value per inch insulation over the top plates. This could be rigid insulation that is R-5 or greater per inch, such as extruded polystyrene or polyisocyanurate, or closed-cell spray foam. Rigid foam block could also serve as the insulation dam and baffle to provide protection for soffit vents and ventilating air flow. 

    See the Compliance tab for 2009 IECC-specified wall insulation levels.  Some building scientists note that fully vented, pitched attic assemblies can be the lowest cost, highest R-value, and most durable roofs in all climates zones (except perhaps IECC Zone 1 and Zone 2 with high coastal humidity), as long as no major sources of potential air leakage (e.g., HVAC ducts or recessed light fixtures) are present in the ceiling plane. Given the low cost, high insulation levels (R-60 to R-100) are affordable and economically justified in Zones 5 through 8 and the only change required to meet these high levels, other than an airtight ceiling, is to construct raised heel trusses or rafter designs to accommodate the increased amount of insulation (Straube and Grin 2010).

    How to Construct a Roof with Full Insulation at the Eaves

    1. Order and install oversized or raised heel trusses (Figure 3), or install site-built rafters with raised top plates (Figure 4). Specify 2- to 2½-foot overhangs, which are higher, providing more room for insulation at the top plate and additional window shading.
    2. Install baffles and soffit dams at each rafter bay to provide a clear path for ventilation air above the insulation and to prevent insulation from falling into the soffit vents.
      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 (Source: Georgia State Supplements and Amendments to the International Energy Conservation Code 2011). 
      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 (Source: Georgia State Supplements and Amendments to the International Energy Conservation Code 2011). 
    3. For cathedral roofs, specify and install parallel chord trusses (Figure 5).
      In cathedral ceilings, parallel chord trusses allow thicker insulation levels over the exterior wall top plates.
      Figure 5. In cathedral ceilings, parallel chord trusses allow thicker insulation levels over the exterior wall top plates (Source: Courtesy of PNNL). 
    4. Install attic rulers to show that blown insulation is installed to the proper depth. (The rules should be installed with numbering facing the attic entrance; one ruler for every 300 ft2).
    5. Fill the attic with blown, spray foam, or batt insulation to at least the required minimum insulation level. Blown or spray foam insulation should cover the tops of the ceiling joists. Batts should completely fill the joist cavities; an additional layer of batts can be layed over top of and running perpendicular to the joists. Shake batts to ensure proper loft. If joist spacing is uneven, fill any gaps with scrap pieces of insulation. Cut slits in batt insulation to fit around wiring, plumbing, or ductwork without compressions.
    Success
    Ensuring Success

    The quality of the insulation installation should be visually inspected by the site supervisor. It may be possible to detect heat loss at the tops of exterior walls with an infrared camera if a sufficient temperature difference exists between the outside and the conditioned space of the house. Attic rulers should be installed upright from the ceiling deck and facing the attic entrance, one ruler for every 300 ft2 including at the eaves, to make it easier for the inspector to confirm that proper insulation depth has been achieved.

    Climate
    Climate

     

    Hurricane and High Wind Zones

    When engineered trusses are used with raised heels  in regions designated as hurricane or high wind areas, blocking and continuous sheathing should be installed around the raised heel as bracing to resist displacement. Raised heel trusses have been found in laboratory testing to experience high top cord and rotational displacement compared to a low heel trusses during lab-simulated seismic events (NAHB Research Center 2011).

    Cold Climate Zones

    Adequate insulation and ventilation over exterior wall top plates is especially critical in colder climates with extended periods of snow cover or high snow loads, to reduce the risk of ice dam formation.

    Insulation Requirements

    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)

     

    Training
    Right and Wrong Images
    Image
    Wrong – Framing will not allow for required insulation depth
    Wrong – Framing will not allow for required insulation depth
    Image
    Right – Framing allows for required insulation depth
    Right – Framing allows for required insulation depth
    Image
    Wrong – Framing and wind baffle installation will not allow for required insulation depth
    Wrong – Framing and wind baffle installation will not allow for required insulation depth
    Image
    Right - Continuous wall sheathing and blocking has been installed to brace the raised heel trusses
    Right - Continuous wall sheathing and blocking has been installed to brace the raised heel trusses
    Image
    Spray foam insulates the attic eave between the attic floor and the SIP roof panel.
    Spray foam insulates the attic eave between the attic floor and the SIP roof panel.
    Videos
    CAD
    CAD Files
    1 inch exterior insulation sheathing as attic eave baffle and vent
    1 inch exterior insulation sheathing as attic eave baffle and vent
    Download: DWG PDF
    1 inch rigid insulation as attic eave baffle cut around manufactured vent
    1 inch rigid insulation as attic eave baffle cut around manufactured vent
    Download: DWG PDF
    Thin-profile attic eave baffle and vent
    Thin-profile attic eave baffle and vent
    Download: DWG PDF
    Turned down concrete slab - 1 inch rigid insulation
    Turned down concrete slab - 1 inch rigid insulation
    Download: DWG PDF
    Turned down concrete slab - 1 1/2 inch rigid insulation
    Turned down concrete slab - 1 1/2 inch rigid insulation
    Download: DWG PDF
    Turned down concrete slab - 3/4 inch rigid insulation
    Turned down concrete slab - 3/4 inch rigid insulation
    Download: DWG PDF
    Compliance

    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.
    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 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 Single-Family New 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.
    Footnote 13) Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 2015 IECC – Table 402.2.6. Compliance can be determined by meeting Zero Energy Ready Home requirements based on prescriptive insulation requirements, or U-factor alternatives. 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.

     

    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 402.1.1 lists ceiling R values by climate zone: CZ 1-3: R-30, CZ 4-5: R-38, CZ 6-8: R-49.
    Section 402.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.

    2012 IECC

    Table 402.1.1 lists ceiling R values by climate zone: CZ 1: R-30, CZ 2-3: R-38, CZ 4-8: R-49.
    Section 402.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.

    2015 IECC and 2018 IECC

    Table 402.1.2 lists ceiling R values by climate zone: CZ 1: R-30, CZ 2-3: R-38, CZ 4-8: R-49.
    Section 402.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.

    2021 IECC

    Table 402.1.3 lists ceiling R values by climate zone:  CZ 0: R-30 CZ 1: R-30, CZ 2-3: R-49, CZ 4-8: R-60.
    Section 402.2.1, Ceilings with attic spaces. R-38 will satisfy the requirement for R-49 insulation on the ceiling if the R-38 is uncompressed and extends over the top plates at the eaves. In the same way, R-49 suffices in climate zones requiring R-60 attic insulation.

    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, 2020). 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 1102.1.1 lists ceiling R values by climate zone: CZ 1-3: R-30, CZ 4-5: R-38, CZ 6-8: R-49.
    Section 1102.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.  

    2012 IRC

    Table 1102.1.1 lists ceiling R values by climate zone: CZ 1: R-30, CZ 2-3: R-38, CZ 4-8: R-49.
    Section 1102.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.

    2015 and 2018 IRC

    Table 1102.1.2 lists ceiling R values by climate zone: CZ 1: R-30, CZ 2-3: R-38, CZ 4-8: R-49.
    Section 1102.2.1, Ceilings with attic spaces. R-30 will satisfy the requirement for R-38 insulation on the ceiling if the R-30 is uncompressed and extends over the top plates at the eaves. In the same way, R-38 suffices in climate zones requiring R-49 attic insulation.

    Section R905.1.2 (Section R905.2.7.1 in 2012 and 2009) specifies ice barrier requirements for geographic areas where there has been a history of ice dams. Requirements apply to asphalt shingle roofs, metal roof singles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. An exception is included for detached accessory structures not containing conditioned floor area.

    Section R905.7.1.1 (Section R905.8.1.1 in 2009) states that in areas where the average daily temperature in January is 25°F (-4°C) or less, solid sheathing is required on that portion of the roof requiring the application of an ice barrier.

    Section R805.6 discusses vapor retarder and insulation requirements for unvented attics and unvented enclosed rafter assemblies in cold climates.

    Table R806.5 (R806.4 in 2009) specifies roof-ceiling insulation requirements for condensation control based on climate zone.

    2021 IRC

    Table 1102.1.2 lists ceiling R values by climate zone: CZ 0: R-30, CZ 1: R-30 CZ 2-3: R-49, CZ 4-8: R-60.
    Section 1102.2.1, Ceilings with attic spaces. R-38 will satisfy the requirement for R-49 insulation on the ceiling if the R-38 is uncompressed and extends over the top plates at the eaves. In the same way, R-49 suffices in climate zones requiring R-60 attic insulation.

    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.

    Retrofit
    Existing Homes

    SCOPE

    Installing raised heel roof trusses, as described for new homes, is beyond the scope of most retrofits but energy performance of existing roofs can often be improved by adding air sealing, insulation and baffles.

    • Provide a pathway for air to flow from soffit vents to the main part of the attic and up toward the ridge by installing or verifying installation of baffles.
    • Prior to installing insulation, carefully clear, clean, and air seal the top plates along all exterior walls.
    • Install insulation in the eave areas to the maximum height possible.

    Assess the attic as described in the guide titled Pre-Retrofit Assessment of Attics, Ceilings, and Roofs. In ventilated attics, ensure there is adequate ventilation as described in the guide on Calculating Attic Passive Ventilation.

    Air sealing can impact indoor air quality and the air available for combustion appliances to work properly. Before starting the air sealing read and conduct the assessments described in the Pre-Retrofit Assessment of Combustion Appliances and the Pre-Retrofit Assessment of Hazardous Materials.

    The U.S. Department of Energy’s Standard Work Specifications (SWS) define minimum requirements to ensure that the work performed during home energy upgrades is effective, durable, and safe. The Standard Work Specifications include specifications for the following topics, which may be applicable to insulating soffits.

    • Global worker safety.
    • Worker health and safety specifications related to air sealing.
    • General air sealing attics.
    • Insulating attic ceilings.
    • Soffit ventilation and baffles.
    • Combustion safety, which may be impacted by air sealing.

    DESCRIPTION

    The techniques described in this guide for new homes require incorporating structural design features such raised heel trusses that allow for the full depth of insulation in the attic eaves. This approach is not feasible in existing homes that do not have specially designed roof trusses. However, attic eaves in existing home can be insulated to the extent that space allows while still permitting adequate ventilation.

    Prior to installing insulation, carefully clear, clean, and air seal the top plates for all exterior walls. Clearing this area may involve rolling back or moving insulation that is in the rafter cavities. Use a continuous bead of sealant or spray foam to seal the seam between the top plate and the gypsum board. The seam may also be sealed with rigid foam, sheet goods, or reflective foil insulation that is glued in place and sealed along all edges. Seal all penetrations through the soffits that are not part of the air vents and confirm that screening over soffit vents is securely in place; these steps will help stop the entry of pests and wind-blown rainwater.

    Install baffles as described for new homes in the Description tab. In addition to the approach described for new homes, baffles may also be supported using spray foam or rolled fiberglass batts to form a backstop for the baffles. If the baffles will block access to the wall top plate, seal the top plate before installing the baffle.

    Completely fill the space between the attic floor and the attic-side of the baffles with blown-in, batt, or spray-foam insulation. Use insulating material with the highest R-value to achieve the best success in the limited space. Spray foam has the advantage of combining air-sealing with insulation and will conform well to the sloping contour of the roof and the complex shape of the rafters.

    For more information on related topics see the following guides.

    Batt Insulation for Existing Vented Attics

    Guide describing how to increase insulation in existing homes by installing batt insulation on the ceiling plane of a vented attic.

    Blown Insulation for Existing Vented Attic

    Guide describing how to insulate a vented attic in an existing home using blown insulation added to the attic floor.

    Ducts Buried in Attic Insulation

    This guides describes buried ducts in loose-fill attic insulation, a method that can only be used in dry climates.

    Wind Washing

    Guide describing wind washing and how to prevent it.

    SUCCESS

    Before insulating the attic floor, clear, clean, and air seal the top plates where all interior walls intersect the attic floor.

    COMPLIANCE

    See Compliance tab. 

    More

    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)
    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)
    U.S. Department of Energy
    Organization(s)
    DOE
    Publication Date
    Description
    Information sheet with the definition and uses for a raised truss.
    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)
    NAHB,
    Southface Energy Institute,
    Oak Ridge National Laboratory,
    National Renewable Energy Laboratory
    Organization(s)
    NAHB,
    Southface Energy Institute,
    Oak Ridge National Laboratory,
    National Renewable Energy Laboratory
    Publication Date
    Description
    Information sheet about advanced wall framing.
    Author(s)
    Straube,
    Grin
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Report that considers a number of promising wall systems that can meet the requirement for better thermal control.
    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.
    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)
    Baechler Michael C,
    Gilbride Theresa L,
    Hefty Marye G,
    Cole Pam C,
    Williamson Jennifer,
    Love Pat M
    Organization(s)
    Pacific Northwest National Laboratory,
    PNNL,
    Oak Ridge National Laboratory,
    ORNL
    Publication Date
    Description
    Report identifying the steps to take, with the help of a qualified home performance contractor, to seal unwanted air leaks while ensuring healthy levels of ventilation and avoiding sources of indoor air pollution.
    *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.

    Sales
    Building Science Measures
    Building Science-to-Sales Translator

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

    Image(s)
    Technical Description

    There are two levels of attic 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 Attic Insulation
    Sales Message

    High-efficiency attic 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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