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Batt Insulation for Existing Vented Attics

    Scope
    Scope Images
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    Batt insulation is installed at the attic floor
    Scope

    Insulate a vented attic in an existing home by installing batt insulation on the ceiling plane of the attic, as follows:

    • Before any retrofit work is done, inspect the roof and attic; repair any leaks, remove active knob and tube wiring, and remediate any hazardous materials.
    • If existing bath fans vent into the attic, they must be vented to the outside.
    • Remove any existing insulation, debris and dust, and prepare the attic floor for air sealing and fibrous batt insulation.
    • Seal all attic floor penetrations with sealant, one-part spray foam, or rigid blocking material as needed.
    • Verify that proper ventilation of the attic is provided with soffit vents (preferred) or gable and ridge vents. Verify that there is a baffle at each soffit vent extending from the top plate to above the height of the insulation to provide a pathway for ventilation air while keeping insulation out of the soffit vents.
    • Install batt insulation over the attic floor to levels that meet or exceed the current adopted building and energy codes.

    This approach is suitable for projects with a vented attic where the thermal boundary is established at the attic floor/ceiling plane. This approach requires that there be sufficient height between the underside of the roof deck and the top plate at the eave to install the full code-required amount of insulation while maintaining an air gap for ventilation above the insulation. Installing HVAC ducts and air handlers in vented attics is not recommended.

    See the following Building America Solution Center guides for more information:

    See the U.S. Department of Energy’s Standard Work Specifications (SWS) for more guidance on installing batt insulation and batt insulation over existing insulation.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

    Description
    Description

    Many older homes have little or no attic insulation. Batt insulation can be installed at the ceiling plane/attic floor to improve thermal performance in a vented attic.

    When attic batt insulation is installed in two layers (Figure 1), the first layer of batts is typically installed between and parallel to the ceiling joists and the second layer is typically run perpendicular to the first layer, to cover the tops of the joists, thus stopping thermal bridging through the joists. The second layer could also be installed parallel to the first layer of batts but with the batts offset so that the seams don’t line up. The batts should be split to fit snugly around any wiring or pipes. The batts should be installed in accordance with RESNET Grade 1 installation criteria (See BASC guide: Insulation Installation Achieves RESNET Grade I as well as Insulation Installation [RESNET Grade 1] - Part 1 and Insulation Installation [RESNET Grade 1] - Part 2).

    The ceiling plane or attic floor should be thoroughly air sealed prior to installing insulation. Robust and continuous air control is critical to a high-performance thermal enclosure. The existing insulation must be removed to provide access to the ceiling plane for air sealing. Debris and dust should also be removed so that sealants will have good adhesion. Seal all cracks, seams and holes using caulk or spray foam sealants. Use solid blocking for any larger holes or open soffits. Metal blocking and collars can be constructed around hot flues to keep insulation from touching them. Covers can be purchased or constructed to cover, air seal, and insulate recessed can lights that are not insulated ceiling airtight (ICAT) rated. (See Attic Air Sealing Guide and Details.)

    If existing insulation was removed from the attic floor to perform air sealing, it may be reinstalled if it is in good condition.  However, existing attic insulation is often contaminated with construction debris, plaster scraps, animal droppings, etc. Older loose-fill may be vermiculite insulation which can contain asbestos. The safest approach may be to dispose of the old insulation and install only new insulation.

    Guidance for mitigating asbestos-related issues from HUD, EPA, NIH, OSHA and FEMA is available in Homeowner's and Renter's Guide to Asbestos Cleanup After Disasters and Asbestos: Worker and Employer Guide to Hazards and Recommended Controls

    The presence of flooring above the ceiling joists in an attic will make it difficult to air seal at the ceiling plane (attic floor).  If the air control is to be established at the ceiling plane, then any attic flooring installed above that must be removed to provide full access to the ceiling surface.  Alternately, it may be possible to transition the air barrier to the top of the existing attic floor. To successfully execute this option, sufficient insulation is required outboard (on top of) the floor to control condensation and a robust air control connection must be made from the top of the exterior walls to the perimeter of the attic flooring.

    In climate zones 6 or higher, a Class I vapor barrier (e.g., polyethylene) or Class II vapor retarder should be installed above the ceiling drywall as required by code. Class I vapor barriers should be avoided in climate zones 5 and below, as condensation can occur on the attic side of the vapor barrier in summer months during air conditioning periods. (See BSD 102 Attic Ventilation.)

    One benefit of a vented (rather than unvented) attic is that interior-sourced moisture will be vented out of the attic space before causing damage to the roof sheathing. Another advantage of vented attics in cold climates is that they help to reduce the chances of ice damming on the roof. Ice dams occur when heat leaks from the conditioned space (through holes in the ceiling plane, insufficient insulation, or heat loss from ductwork) and melts the snow on the roof. This melted snow travels down to the edges of the roof where it refreezes, creating icicles and ice dams. Attic ventilation helps to “flush away” this heat before it can melt the snow. (See BSI-046: Dam Ice Dam, and BSD-135: Ice Dams.)   

    The vented attic approach requires that there be sufficient height at the attic eaves for code-level required amounts of insulation. In mixed- and cold climates (zones 4 and above), inadequate insulation raises risks of wintertime condensation at the top plate due to cold surfaces. If the roof is too low at the eaves to install adequate amounts of batt insulation, then alternative solutions are to fill the space over the top plate to the baffle with closed-cell spray foam or to cover the top plate area with rigid foam board. (Spray foam and rigid foam have higher R-values per inch than blown insulation. Spray foam has the added advantage of air sealing the top plate-to-drywall seams and the baffle-to-top plate seam.) Another option is to convert the attic to a sealed, insulated space by sealing the soffit vents and insulating along the underside of the ceiling deck with closed-cell spray foam or above the roof deck with rigid foam. In new home construction, a common solution to increase the roof height for insulation above the top plate is to use raised heel trusses. Older existing roofs are unlikely to have raised heel trusses and raised heel trusses are not likely to be installed as a retrofit measure unless a complete reconstruction of the roof is required, for example if a second or third story is being added.

    The vented attic approach requires that there be sufficient height at the attic eaves to maintain an air gap above the insulation for ventilation air traveling from the soffit vents to the ridge vents. The vent space should be at least 2 inches high and the width of the framing bay at each soffit vent (Lstiburek 2006). Baffles should be installed at each soffit vent to provide this pathway for ventilation air to move up past the insulation along the underside of the roof deck to ridge vents or mushroom cap vents located near the ridge. The lower edge of the baffle can be sealed to the attic floor at the outside edge of the top plate with spray foam, which also air seals the top plate-to-dry wall seams. The baffles also serve to prevent insulation from covering the soffit vents and they can prevent “wind washing,” i.e., when wind blows in the soffit vents and pushes the insulation back from the eaves.

    If the attic does not have soffit vents, attic ventilation can be provided by installing other types of vents such as gable or eyebrow vents down low near the attic floor, along with ridge vents or mushroom cap vents located up near the roof ridge.

    Powered attic ventilators (thermostatically controlled fans that exhaust attic air during hot weather) can result in increased infiltration (and associated higher cooling loads).  Studies have shown that powered ventilators have higher electricity consumption than their associated air conditioner savings (FSEC 2005/ Literature Review of the Impact and Need for Attic Ventilation in Florida Homes).

    Installing HVAC ducts and air handlers in vented attics is not recommended. Locating ductwork and/or air handling equipment in a vented attic can contribute to energy losses, performance issues, and ice dam formation in snowy climates, especially if the ducts and air handlers are leaky or poorly insulated.  One exception is if the ductwork can be encapsulated in spray foam and buried beneath the attic floor batt insulation. The ducts must be tightly air sealed and covered with a sufficient amount of spray foam insulation to minimize the risk of condensation forming on the outside of the ducts. See Ducts Buried in Attic Insulation.  However, because mechanical equipment such as air handlers cannot be adequately air sealed, locating them in a vented attic is not recommended. If the air handler must be located in the attic then consider converting the attic to a sealed, insulated space.

    Batt insulation is installed at the attic floor.
    Figure 1. Batt insulation is installed at the attic floor (Source: Courtesy of Building Science Corporation). 

     

    How to Insulate Attic Floor with Batt Insulation

    1. Before any retrofit work is done, inspect the work area for active knob and tube wiring, bathroom fans venting into attics, roof leaks, and other hazardous conditions. Repair these conditions prior to adding insulation. Inspect for and remove or remediate hazardous materials like asbestos-containing vermiculite insulation.
    2. Remove any existing insulation, debris, and dust from the floor of the attic, and clean the work area to allow for adequate adhesion of sealants.
      Clean the attic floor of debris prior to installing new attic insulation. Use baffles to provide a path for ventilation air entering the attic from the soffit vents.
      Figure 2. Clean the attic floor of debris prior to installing new attic insulation. Use baffles to provide a path for ventilation air entering the attic from the soffit vents (Source: Attic Air Sealing Guide and Details, GM-1001 2010). 
    3. Seal all ceiling joints and penetrations with sealant. Seal top plate-to-drywall seams and top plate-to-baffle seams. Provide additional solid blocking for large holes and open soffits, install metal blocking and collars around hot flues, and install covers over non-ICAT-rated recessed can lights.  (See BSC. 2013. Attic Air Sealing Guide and Details).  Don’t block intentional openings such as combustion air ducts and soffit, ridge, and gable vents.
      Seal drywall to top-plate seams. Seal lower edge of baffle to top plate to prevent incoming air from soffit vents from flowing under baffles into insulation.
      Figure 3. Seal drywall to top-plate seams. Seal lower edge of baffle to top plate to prevent incoming air from soffit vents from flowing under baffles into insulation (Source: Attic Air Sealing Guide and Details, GM-1001 2010). 
      Seal all drywall-to-top plate seams and penetrations at the attic floor.
      Figure 4. Seal all drywall-to-top plate seams and penetrations at the attic floor (Source: Attic Air Sealing Guide and Details, GM-1001 2010). 
    4. Verify that proper ventilation of the attic is provided with soffit and ridge vents or eyebrow, gable end, mushroom cap, and/or other vents. (See Figure 5.) If soffit vents exist, inspect existing baffles and install new baffles if needed. (See Figure 3.)
      Attic ventilation approaches.
      Figure 5. Attic ventilation approaches (Source: Courtesy of Building Science Corporation). 
    5. Install batt insulation over the attic floor to levels that meet or exceed the current adopted building and energy codes for thermal performance.  When applicable, install the insulation in two layers in perpendicular directions (or alternately, with offset seams), with the second layer over the ceiling joists, to control thermal bridging.  Cover the entire ceiling ensuring that the batts cover the exterior wall top plates and are in contact with the baffles to provide adequate thermal resistance at the eaves.
    Batt insulation is installed in two layers in perpendicular directions against the baffle to full required insulation height.
    Figure 6. Batt insulation is installed in two layers in perpendicular directions against the baffle to full required insulation height (Source: Attic Air Sealing Guide and Details, GM-1001 2010). 

     

    Batt insulation is installed in two layers with offset seams against the baffle to full code-required insulation height.
    Figure 7. Batt insulation is installed in two layers with offset seams against the baffle to full code-required insulation height (Source: Attic Air Sealing Guide and Details, GM-1001 2010). 

     

    Success
    Ensuring Success

    Remediate any hazardous conditions that will be affected (e.g., exposed or aggravated) by the planned work. Examples of hazardous materials that may be found in attic/roof assemblies of existing structures include (but are not limited to) lead, asbestos, mold, animal dropping/remains, etc. Follow applicable laws and industry procedures for mitigation of hazardous materials. Engage the services of a qualified professional when needed.

    For more information on vermiculite, see the EPA guide: Protect Your Family from Asbestos – Contaminated Vermiculite Insulation.

    For guidance on handling knob and tube wiring, see Weatherization Assistance Program guide: Retrofitting Insulation in Cavities with Knob-and-Tube Wiring an Investigation into Codes, Safety, and Current Practices.

    Seal all penetrations to provide a continuous air control layer at the attic floor. Visual inspection, infrared thermography, and blower door testing are all tools that can be used to verify air barrier continuity.

    Install batt insulation to provide adequate thermal resistance and to the levels specified in the current adopted building and energy codes.

    Electrical junction boxes accessible from the attic will be buried during this insulation retrofit.  The NEC (Article 314.29, 2005 NEC) requires junction boxes to be accessible "without removing any part of the building."  This clause could be interpreted as including or excluding attic insulation.  The ideal approach would elevate the junction box above the insulation level; alternately, a flag marker could be placed to indicate junction box location.  A local code official could provide further guidance.

    All vented roofs must have an adequate amount of venting according to the applicable current adopted building code.  If the roof is not vented according to the applicable building code then a qualified contractor in the state should be engaged to install the necessary venting.

    Climate
    Climate

    The ceiling/attic floor 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. 

    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).

     

    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. The table below provides the minimum thermal resistance (R-value) requirements specified in the 2009 IECC (ICC 2009b) and the 2012 IECC (ICC 2012b) based on climate zone for ceiling/attic floor assemblies.

    Attic Insulation Requirements per the 2009 and 2012 IECC.

    Table 1. Attic Insulation Requirements per the 2009 and 2012 IECC.

     

    Training
    Right and Wrong Images
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    Wrong - Batt insulation does not provide complete coverage across the attic floor. Ceiling joists are exposed resulting in thermal bridging
    Wrong - Batt insulation does not provide complete coverage across the attic floor. Ceiling joists are exposed resulting in thermal bridging
    Image
    Right – Batt insulation provides additional insulation for the home’s main duct chase.
    Right – Batt insulation provides additional insulation for the home’s main duct chase.
    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
    Wrong - Batt insulation is poorly installed leaving gaps along the ceiling.
    Wrong - Batt insulation is poorly installed leaving gaps along the ceiling.
    Videos
    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)

    ENERGY STAR Single-Family New Homes requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009 International Energy Conservation Code (IECC) with some alternatives and exceptions, and achieve Grade 1 installation per RESNET Standards (see 2009 and 2012 IECC Code Level Insulation – ENERGY STAR Requirements as well as Insulation Installation (RESNET Grade 1) - Part 1 and Insulation Installation (RESNET Grade 1) - Part 2. If the state or local residential building energy code requires higher insulation levels than those specified in the 2009 IECC, you must meet or exceed the locally mandated requirements. Some states have adopted the 2012 or 2015 IECC. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state.

    National Rater Design Review Checklist

    3. High-Performance Insulation.
    3.1 Specified ceiling, wall, floor, and slab insulation levels comply with one of the following options:
    3.1.1 Meets or exceeds 2009 IECC levels5, 6, 7 OR;
    3.1.2 Achieves ≤ 133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, per guidance in Footnote 5d, AND specified home infiltration does not exceed the following:6, 7

    • 3 ACH50 in CZs 1, 2
    • 2.5 ACH50 in CZs 3, 4
    • 2 ACH50 in CZs 5, 6, 7
    • 1.5 ACH50 in CZ 8

    Footnote 5) Specified levels shall meet or exceed the component insulation levels in 2009 IECC Table 402.1.1. The following exceptions apply:
    a. Steel-frame ceilings, walls, and floors shall meet the insulation levels of 2009 IECC Table 402.2.5. In CZ 1 and 2, the continuous insulation requirements in this table shall be permitted to be reduced to R-3 for steel-frame wall assemblies with studs spaced at 24 in. on center. This exception shall not apply if the alternative calculations in d) are used;
    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 or less than specified in 2009 IECC Table 402.1.3 complies. A total building thermal envelope UA that is less than or equal to the total UA resulting from the U-factors in Table 402.1.3 also complies. The performance of all components (i.e., ceilings, walls, floors, slabs, and fenestration) can be traded off using the UA approach. Note that Items 3.1 through 3.3 of the National 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 6) Consistent with the 2009 IECC, slab edge insulation is only required for slab-on-grade floors with a floor surface less than 12 inches below grade. Slab insulation shall extend to the top of the slab to provide a complete thermal break. If the top edge of the insulation is installed between the exterior wall and the edge of the interior slab, it shall be permitted to be cut at a 45-degree angle away from the exterior wall. Alternatively, the thermal break is permitted to be created using ≥ R-3 rigid insulation on top of an existing slab (e.g., in a home undergoing a gut rehabilitation). In such cases, up to 10% of the slab surface is permitted to not be insulated (e.g., for sleepers, for sill plates). Insulation installed on top of slab shall be covered by a durable floor surface (e.g., hardwood, tile, carpet).

    Footnote 7) Where an insulated wall separates a garage, patio, porch, or other unconditioned space from the conditioned space of the house, slab insulation shall also be installed at this interface to provide a thermal break between the conditioned and unconditioned slab. Where specific details cannot meet this requirement, partners shall provide the detail to EPA to request an exemption prior to the home’s certification. EPA will compile exempted details and work with industry to develop feasible details for use in future revisions to the program. A list of currently exempted details is available at: energystar.gov/slabedge.

    Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable 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 2, 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.

     

     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, 2012, 2015, 2018, and 2021 International Energy Conservation Code (IECC)

    Section 101.4.5 (R502.1.2 in 2018, R502.2 in 2021) Change in space conditioning.  This section states that spaces must be brought into full compliance with the new construction requirements if the addition, alteration, renovation or repair changes that space from unconditioned to conditioned space.

    Section 402 Building Thermal Envelope. Table 402.1.1 (R402.1.2 in 2018, R402.1.3 in 2021) indicates the prescriptive requirements for building enclosure components.

    Section 402.2.1 Ceilings with attic spaces. This section indicates that the prescriptive requirement for R-38 ceiling insulations is deemed to be met by R-30 insulation when the R-30 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves.  Similarly, R-38 insulation is recognized to satisfy the requirement for R-49 insulation when R-38 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves. (In the 2021 IECC, this reduction is extended to the requirement for R-60 insulation, stating that R-45 can satisfy the requirement where insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves. )

    Section 402.3. (402.2.4 in 2018 and  2021) Access hatches and doors. Doors or hatches separating conditioned spaces from unconditioned spaces (such as attics and crawl spaces) must be weather stripped and insulated to a level equivalent to that of surrounding assemblies.  When loose fill insulation is used, insulation dams are required around attic hatches.

    Section 402.4 Air Leakage.  This section indicates that the building thermal envelope (as it is called in the IECC) must be sealed to limit infiltration and that it must be sealed in a manner that is durable allowing for differential expansion and contraction.

    Portions of an existing building that are altered in the course of additions, alterations, renovations or repairs must be brought into conformance with the code with the following exceptions applicable to attic/roof retrofit: existing ceiling wall or floor cavities that are exposed provided the cavities exposed are filled with insulation; addition, alteration, renovation or repair projects that do not expose the existing roof, wall or floor cavity; reroofing that does not expose the insulation nor the sheathing.

    Section R402.2.3 Eave baffle.  This section indicates the requirement for baffles to be installed next to eave and soffit vents for vented attics using air permeable insulations.  The baffle can be any solid material, must extend to the top of the attic insulation, and must maintain an opening that is at least as large as the vent.
    Note that baffles should also be used with vented cathedral assemblies.

    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)

    Appendix J, Section 501.6, Ventilation.  The appendix is not attached to the requirements of the IRC unless it is specifically included by the adopting jurisdiction.  This section of the appendix indicates that any space that is changed to be habitable or occupiable by alteration must be provided with ventilation in accordance with Section R303.

    Section R806.3 Vent and insulation clearance.  A vent space clearance of at least 1” must be maintained at the location of the vent and between insulation and roof sheathing.
    Note that this would not apply where an unvented roof assembly is used as indicated in section R806.4.

    Section R807.1 Attic access.  An attic access is required where the ceiling or roof construction is combustible and where the attic area is more than 30 sf and the height between the ceiling framing and roof framing is more than 30”.  Refer to specific language of this section for required dimensions of the access.

    Section N1102.2.1 Ceilings with attic spaces. This section indicates that the prescriptive requirement for R-38 ceiling insulations is deemed to be met by R-30 insulation when the R-30 insulation extends over the wall top plate at the eaves and when the insulation is at full loft and uncompressed over the wall top plate at the eaves.  Similarly, R-38 insulation is recognized to satisfy the requirement for R-49 insulation when R-38 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves.

    Section N1102.2.3 Access hatches and doors. Doors or hatches separating conditioned spaces from unconditioned spaces (such as attics and crawl spaces) must be weather-stripped and insulated to a level equivalent to that of surrounding assemblies.  When loose fill insulation is used, insulation dams are required around attic hatches.

    Section N1102 Building Thermal Envelope. Table N1102.1 indicates the prescriptive requirements for building enclosure components.

    Section N1102.4 Air Leakage.  This section indicates that the building thermal envelope (as it is called in the IRC) must be sealed to limit infiltration and that it must be sealed in a manner that is durable allowing for differential expansion and contraction.

    2009, 2012, 20152018, and 2021 IRC

    Section R806.3 Vent and insulation clearance.  A vent space clearance of at least 1” must be maintained at the location of the vent and between insulation and roof sheathing.

    Section R806.4 Installation and weather protection.  This section indicates that ventilators for roofs are to be installed in accordance with manufacturer’s installation instructions and the requirements of Section R903.

    Section R807.1 Attic access.  An attic access is required where the ceiling or roof construction is combustible and where the attic area is more than 30 sf and the height between the ceiling framing and roof framing is more than 30”.  Refer to specific language of this section for required dimensions of the access.

    Section R901 Roof Assemblies.  This section outlines the design, materials, construction and quality of roof assemblies.

    Section N1102 Building Thermal Envelope. Table N1102.1.1 (N1102.1.2 in 2015 and 2018 IRC) indicates the prescriptive requirements for building enclosure components.

    Section N1102.2.1 Ceilings with attic spaces. This section indicates that the prescriptive requirement for R-38 ceiling insulations is deemed to be met by R-30 insulation when the R-30 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves.  Similarly, R-38 insulation is recognized to satisfy the requirement for R-49 insulation when R-38 insulation extends over the wall top plate at eaves and when the insulation is at full loft and uncompressed over the wall top plate at eaves.

    Section N1102.2.3 Eave baffle.  This section indicates the requirement for baffles to be installed next to eave and soffit vents for vented attics using air permeable insulations.  The baffle can be any solid material, must extend to the top of the attic insulation, and must maintain an opening that is at least as large as the vent.
    Note that baffles should also be used with vented cathedral assemblies.

    Section N1102.2.4 Access hatches and doors. Doors or hatches separating conditioned spaces from unconditioned spaces (such as attics and crawl spaces) must be weather-stripped and insulated to a level equivalent to that of surrounding assemblies.  When loose fill insulation is used, insulation dams are required around attic hatches.

    Section N1102.4 Air Leakage.  This section indicates that the building thermal envelope (as it is called in the IRC) must be sealed to limit infiltration and that it must be sealed in a manner that is durable allowing for differential expansion and contraction.

    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.

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    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
    References and Resources*
    Author(s)
    Neuhauser Ken,
    Gates Cathy,
    Pettit Betsy
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Guidebook providing useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate.
    Author(s)
    Lstiburek Joseph W
    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 Joseph W
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    BSD-102 report providing guidance about whether to construct a vented or unvented attic based on hygro-thermal zone.
    Author(s)
    Straube John
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Article outlining the casuses and solutions for ice dam problems.
    Author(s)
    Lstiburek Joseph W
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Article describing strategies for reducing the risk of ice dam formation on roofs in winter.
    Author(s)
    National Institution of Health,
    U.S. Environmental Protection Agency,
    U.S. Department of Housing and Urban Development,
    Occupational Safety and Health Administration
    Organization(s)
    NIH,
    OSHA,
    EPA,
    HUD
    Publication Date
    Description
    Guidance from HUD, EPA, NIH, and FEMA for workers who deal directly with asbestos.
    Author(s)
    Centers for Disease Control and Prevention,
    U.S. Environmental Protection Agency,
    Federal Emergency Management Agency,
    U.S. Department of Housing and Urban Development,
    National Institutes of Health,
    Hurricane Sandy Rebuilding Task Force
    Organization(s)
    FEMA,
    EPA,
    HUD,
    NIH,
    CDC
    Publication Date
    Description
    Guidance from EPA, FEMA, HUD, and NIH on how to deal with asbestos in homes following natural disasters.
    *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 Corporation, lead for the Building Science Consortium (BSC), a DOE Building America Research Team

    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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