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Spray Foam Insulation Applied to Existing Attic Ceilings

Scope

Insulate an attic in an existing home by installing spray foam (typically closed-cell) on top of the ceiling plane, i.e., on the floor 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, these must be vented to the outside.
  • Remove any existing insulation, debris, and dust, and prepare the attic floor for spray foam insulation.
  • Verify that all attic floor penetrations can be adequately sealed with spray foam insulation.  Provide additional air sealing measures such as sealants or rigid foam blocking of large holes 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 a minimum of 1 inch of spray foam insulation over the attic floor to provide a continuous air control layer. Install the spray foam to meet or exceed code-required R-values or add additional loose-fill or batt fibrous insulation over the 1 inch of spray foam insulation to levels that meet or exceed the current adopted building energy codes.

This approach is suitable for homes 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.

For more guidance on applying spray foam insulation to attic ceilings, see the U.S. Department of Energy’s Standard Work Specifications (SWS).

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

Many older homes have little or no attic insulation and the attic floor/ceiling plane often has numerous air leaks from unsealed drywall-top plate seams, recessed can lights, gaps around vent pipes and wiring, open soffits, etc., that allow conditioned air to escape into the attic.

Gaps around HVAC flue pipes allow conditioned air to leak through blown fiberglass into the attic
Figure 1.  Gaps around HVAC flue pipes allow conditioned air to leak through blown fiberglass into the attic. An IR camera image shows gaps around HVAC flue pipes allow conditioned air to leak through blown fiberglass into the attic. (Image courtesy of Building Science Corporation).

One technique that can both increase attic insulation and air seal the attic is to apply a layer of spray foam to the attic floor, then to install additional blown-in or batt insulation to meet or exceed insulation R-value requirements.

Closed-cell spray foam (ccSPF) is the preferred product for this air barrier application.  Open-cell spray foam (ocSPF) has a rapid and large volume of expansion during installation. This expansion can make application of a continuous uninterrupted layer of foam difficult due to the “billows” and voids created during ocSPF application. In contrast, ccSPF can be more easily applied in a 1-inch layer of consistent thickness.

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).

If there are significant amounts of debris or dust on the floor of the attic, remove the debris and sweep or vacuum the surface before applying the spray foam. Old insulation, dust, and bits of plaster or mortar will interfere with spray foam adhesion, making an effective air seal difficult. Attempting to encapsulate any significant amount of debris with spray foam insulation is not recommended. If the debris contains hazardous materials, it should be removed or remediated regardless of whether the attic is to be outside of conditioned space or included within the thermal enclosure.  For instance, loose-fill vermiculite insulation may contain asbestos. 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)

The presence of flooring above the ceiling joists in an attic will complicate implementation of air sealing 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.  [CAUTION: In some cases, floor sheathing may resist the lateral thrust of roof framing. If floor sheathing is attached to framing that is perpendicular to the slope of the roof (perpendicular to the ridge or eave), do not remove the floor sheathing without first consulting a qualified building professional.] 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 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.)  Note that 2 inches of ccSPF is typically a Class II vapor retarder.

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. Because spray foam has a higher R-value per inch than blown or batt insulation, it should provide adequate insulation R-value, even with low pitch roofs. 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 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 spray foam 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 ductwork and air handling equipment are installed in the attic, options include temporarily removing the equipment (to provide access to the floor below for spray foaming) or converting the attic to an unvented attic that is sealed along the roof line, combined with retrofit duct sealing and testing. 

Closed-cell spray foam is installed to air seal the floor of the existing vented attic then covered with additional loose-fill fibrous insulation
Figure 2. Closed-cell spray foam is installed to air seal the floor of the existing vented attic then covered with additional loose-fill fibrous insulation.

How to Insulate Attic Floor with Spray Foam 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 the spray foam.
    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 3: 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.

  3. Verify that all attic floor penetrations can be adequately sealed with spray foam insulation.  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. Don’t block intentional openings such as combustion air ducts and soffit, ridge, and gable vents.
  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 4.) If soffit vents exist, inspect existing baffles and install new baffles if needed. (See Figure 3.)
    Four attic venting approaches for vented attics that don’t have soffit vents - vents are installed low for incoming air and high for outgoing air
    Figure 4. Four attic venting approaches for vented attics that don’t have soffit vents - vents are installed low for incoming air and high for outgoing air.

  5. Install a minimum of 1 inch of spray foam insulation over the attic floor.  Cover the entire ceiling including up to and over the exterior wall top plates and seal all penetrations to create a continuous air control layer. Install loose-fill fibrous insulation over the spray foam insulation to levels that meet or exceed thermal insulation levels for the current adopted building and energy codes. If roof is low over attic eaves, completely fill those areas with spray foam to baffles to ensure code-minimum or higher insulation levels over the top plates.
    Spray foam insulation is installed to cover the entire attic floor and the juncture of the attic floor, the top plates, and the base of the baffles
    Figure 5. Spray foam insulation is installed to cover the entire attic floor and the juncture of the attic floor, the top plates, and the base of the baffles.

    Loose-fill fibrous insulation is installed over the spray foam on the attic floor and up against the baffles on top of spray foam insulation to full required insulation height
    Figure 6. Loose-fill fibrous insulation is installed over the spray foam on the attic floor and up against the baffles on top of spray foam insulation to full required insulation height.

 

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 large penetrations with rigid blocking 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.

Apply spray foam insulation to a debris- and dust-free surface to provide adequate thermal resistance and to meet or exceed the levels specified in the current adopted building and energy codes.

Follow the spray foam manufacturer’s instructions and guidelines for installation and Spray foam is a material that is essentially “manufactured” when applied at the building site.  Given the importance of this material’s performance, quality control measures should be set in place.  Some key issues include moisture content and temperature of the substrate, applied spray foam layer or “lift” thickness, ratios of the two spray foam components during application, and storage/handling of spray foam components.  Further information is available at the Spray Polyurethane Foam Alliance.

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."  Burying the junction box within the ccSPF layer would clearly violate this requirement, and should not be done.  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 roofs must be vented 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

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. 

IECC climate zones
IECC Climate Zone Map

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

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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

ENERGY STAR Certified Homes (Ver 3.0, Rev 07) requires that ceiling, wall, floor, and slab insulation levels meet or exceed those specified in the 2009 International Energy Conservation Code (IECC).

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 IECC. Visit the U.S. DOE Building Energy Codes Program to see what code has been adopted in each state. For states that have adopted the 2012 IECC or an equivalent code, EPA intends to implement the ENERGY STAR Certified Homes Version 3.1 National Program Requirements for homes permitted starting one year after state-level implementation of the 2012 IECC or an equivalent code. However, EPA will make a final determination of the implementation timeline on a state-by-state basis. Some states and regions of the country have ENERGY STAR requirements that differ from the national requirements. Visit ENERGY STAR’s Regional Specifications page for more information on those region-specific requirements.

The ENERGY STAR Thermal Enclosure System Rater Checklist (Ver 3, Rev 07) specifies:

2.1 Ceiling, wall, floor and slab insulation levels shall comply with one of the following options:

2.1.1 Meet or exceed 2009 IECC levels, OR

2.1.2 Achieve <= 133% of the total UA resulting from the U-factors in 2009 IECC Table 402.1.3, excluding fenestration and per guidance in note “d” below, AND home shall achieve <= 50% of the infiltration rate in Exhibit 1 of the National Program Requirements.

(3) Insulation levels in a home shall meet or exceed the component insulation requirements in the 2009 IECC - Table 402.1.1. The following exceptions apply:

      1. Steel-frame ceilings, walls, and floors shall meet the insulation requirements of the 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 inch on center. This exception shall not apply if the alternative calculations in "d" below are used;
      2. 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;
      3. 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 square feet or 20% of the total insulated ceiling area, whichever is less. This exemption shall not apply if the alternative calculations in "d" are used;
      4. 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 insulation levels of all non-fenestration components (i.e., ceilings, walls, floors, and slabs) can be traded off using the UA approach under both the Prescriptive and the Performance Path. Note that fenestration products (i.e., windows, skylights, doors) shall not be included in this calculation. Also, note that while ceiling and slab insulation can be included in trade-off calculations, the R-value must meet or exceed the minimum values listed in Items 4.1 through 4.3 of the ENERGY STAR Checklist to provide an effective thermal break, 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.

DOE Zero Energy Ready Home

The U.S. Department of Energy Zero Energy Ready Home National Program Requirements specify as a mandatory requirement (Exhibit 1, #2.2) that, for all labeled homes, whether prescriptive or performance path, ceiling, wall, floor, and slab insulation shall meet or exceed 2012 IECC levels. See the guide 2012 IECC Code Level Insulation – DOE Zero Energy Ready Home Requirements for more details.

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

2009 IECC

Section 101.4.3 Additions, alterations, renovations or repairs.  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 101.4.5 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 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.

Section 402.3. 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 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.

20122015, and 2018 IECC

Section R101.4.3 (R501.1.1/R503.1.1 in 2015 and 2018 IECC) Additions, alterations, renovations or repairs.  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 R101.4.5 (R503.2 in 2015 and 2018 IECC) 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 R402 Building Thermal Envelope. Table R402.1.1 (R402.1.2 in 2015 and 2018 IECC) indicates the prescriptive requirements for building enclosure components.

Section R402.2.1 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 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.

Section R402.2.4 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 R402.4 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.

Retrofit: 200920122015, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 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

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.

20122015, and 2018 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.

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: 200920122015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 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.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

  1. Author(s): BA-PIRC
    Organization(s): BA-PIRC
    Publication Date: October, 2013

    Case study describing a multifamily deep energy retrofit project in Annapolis, Maryland.

  2. Author(s): BA-PIRC
    Organization(s): BA-PIRC
    Publication Date: November, 2013

    Case study about a multifamily, affordable housing retrofit project that achieved 44% energy savings using readily available, cost effective measures.

References and Resources*

  1. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2009

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  2. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2009

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  3. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2012

    Code establishing a baseline for energy efficiency by setting performance standards for the building envelope (defined as the boundary that separates heated/cooled air from unconditioned, outside air), mechanical systems, lighting systems and service water heating systems in homes and commercial businesses.

  4. Author(s): International Code Council
    Organization(s): ICC
    Publication Date: January, 2012

    Code for residential buildings that creates minimum regulations for one- and two-family dwellings of three stories or less. It brings together all building, plumbing, mechanical, fuel gas, energy and electrical provisions for one- and two-family residences.

  5. Author(s): Lstiburek
    Organization(s): Building Science Corporation
    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.

  6. Author(s): Pettit, Neuhauser, Gates
    Organization(s): Building Science Corporation
    Publication Date: July, 2013

    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.

  7. Author(s): Lstiburek
    Organization(s): Building Science Corporation
    Publication Date: October, 2006

    Report providing guidance about whether to construct a vented or unvented attic based on hygro-thermal zone.

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

Last Updated: 11/17/2015