Vented vs Unvented Attic

    Scope Images
    Image
    The thermal boundary for a gable roof can be located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic
    Scope

    Determine whether to locate the thermal boundary at the roof line or at the ceiling plane of a home.

    This decision will be based on several factors, including:

    • climate
    • desire for additional living and storage space
    • building design and configuration
    • location of HVAC.

    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

    Where to locate the thermal boundary is an important design consideration when designing the roof-attic-ceiling assemblies in new construction. The thermal boundary consists of the thermal barrier (insulation) and the air barrier (for example, caulked sheathing or mudded and taped drywall). These two layers should both be continuous around the building envelope (walls, ceiling, floor) and they should be in continuous contact with each other.

    In a roof-attic assembly, the builder has two choices: the thermal boundary can be at the ceiling plane, leaving the attic space above uninsulated and vented, or the thermal boundary can be located at the roof line, creating a sealed, insulated, conditioned or semi-conditioned attic space. When the thermal barrier is located at the roof line, it can be either above or below the roof decking. Either way, the attic would be unvented.

    When the thermal boundary is at the ceiling level, the ceiling drywall serves as the air barrier; any gaps around penetrations (for wiring, flues, ducts, etc.) are carefully air sealed. The thermal barrier consists of the insulation (typically blown fiberglass or cellulose, sometimes spray foam and batt), which is piled on top of the ceiling drywall. Vents are installed at the soffits and at or near the ridge, and baffles are installed at each soffit vent to provide a pathway for ventilation air and to keep insulation from blocking the soffit vents. The lower soffit vents are intended to “supply” air to the attic space, and the upper roof/attic vents are intended to “exhaust” air from the attic space. Ridge vents are more effective than button/off-ridge vents in this regard. In general, gable-end vents should not be used in conjunction with ridge or off-ridge vents because the gable-end vents are likely to “short-circuit” attic air flow. 

    In hurricane and high-wind locations and fire-prone locations, the IBHS Fortified Home program recommends not installing gable-end vents in new homes. Use certified, properly installed ridge or off-ridge vents rather than gable vents. For existing homes that have gable vents, either permanently block the gable vents or provide removable or operable exterior or interior coverings or shutters that can be installed when a hurricane or fire threatens and removed when the threat has passed. Permanent mounting anchors should be installed for these coverings. To provide more robust wildfire resiliency, mesh screening should be installed at soffit vent openings. The recommended mesh size is 1/8 inch (3 mm) or less. Ridge vents that are compliant with Miami-Dade wind-driven rain requirements and are effective at wind-driven rain control are also effective in controlling the entry of airborne embers or cinders. 

    See Figures 1 through 3 for examples of thermal boundary locations for vented and unvented attics for three attic designs: flat ceiling/gable roof, low-sloped shed roof, and 1-and ½-story home.  

    The thermal boundary for a gable roof can be located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic.
    Figure 1. The thermal boundary for a gable roof can be located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic (Source: Building Science Corporation).

     

    A low-sloped shed roof with the thermal boundary located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic.
    Figure 2. A low-sloped shed roof with the thermal boundary located at either a) the flat ceiling with a vented attic or b) the roof line for an unvented attic (Source: Building Science Corporation).

     

    A 1- and ½-story home with a room located in the attic and the thermal boundary located at either a) the walls and ceiling of the attic room with small vented attic spaces or b) the roof line for an unvented attic.
    Figure 3. A 1.5-story home with a room located in the attic and the thermal boundary located at either a) the walls and ceiling of the attic room with small vented attic spaces or b) the roof line for an unvented attic (Source: Building Science Corporation).

     

    The key to creating an unvented roof assembly is to keep the roof deck – the principle condensing surface in roof assemblies – sufficiently warm throughout the year such that condensation will not occur, or to prevent interior moisture-laden air from accessing the roof deck. This is done by using air-impermeable insulation such as rigid foam board or spray foam. Rigid foam insulating sheathing is installed on top of the roof sheathing. For more information on this technique, see the guide Above Deck Rigid Foam Insulation for Existing Roofs. Spray foam is installed on the underside of the roof sheathing. For more information on this technique, see the guide Spray Foam Under Roof Sheathing. Both methods require a very high degree of airtightness for avoidance of condensation due to the warming of cold surfaces. For the above-deck rigid foam, air tightness is achieved by installing a continuous membrane over the roof sheathing and under the rigid foam. This membrane could be a peel-and-stick or paint-on membrane or a carefully installed underlayment. For below-deck insulation, the spray foam will provide condensation control. However, all wood-to-wood joints in the framing must still be sealed. In both assemblies, air-permeable insulation (such as batt or loose fill) can be used to increase the overall insulation value. For the above-deck rigid foam option, the batt or blown insulation would go below the decking.  The minimum required thickness of the “air-impermeable insulation” to manage condensation potential is stated in Table R806.5, "Insulation for Condensation Control," of the 2012 IRC. For cold climates, the air-impermeable insulation should be maintained at 50% or more of the total R-value of the roof system for condensation control. For example, if an R-80 unvented cathedralized attic is to be constructed in a cold climate, a minimum of R-40 (50%) should be air-impermeable insulation installed and layered according to Section R806.5 of the 2012 IRC (Figure 4). See the IRC or the guide Unvented Attic Insulation for details.

    Detail of an unvented cathedralized attic showing air-impermeable spray foam insulation plus batt insulation installed on the underside of the roof deck.
    Figure 4. Detail of an unvented cathedralized attic showing air-impermeable spray foam insulation plus batt insulation installed on the underside of the roof deck (Source: Building Science Corporation).

     

    Factors to consider when determining where to locate the thermal barrier in new construction include climate, desire for additional living and storage space, building design and configuration, and location of HVAC. Some factors are listed below. See the Retrofit tab for additional factors that should be considered.

    In coastal locations, hurricane regions, and areas prone to wildfires, it may be advisable to construct an unvented conditioned attic because soffit and roof vents can be an entry point for wind-blown rain and burning embers as well as salt-laden air which can corrode fasteners and HVAC equipment.  While the purpose of soffit vents is to reduce moisture in the attic, in hot humid locations the outside air is likely to be more humid than the inside conditioned air.

    Other reasons for constructing an unvented attic include the following. The builder (or homebuyer if the buyer has purchased prior to construction) may want the attic space to be conditioned for additional living or storage space. The home design may have a complex interior design that would require many transitions between flat ceilings, knee walls, trey ceilings, and/or vaulted ceilings; in cases where numerous transitions make it difficult to achieve a continuous thermal barrier at the ceiling, it may be simpler and thus less expensive to insulate at the roof line. A design decision to have a central ducted heating and cooling system with ducts and air handler located in the attic is another good reason to insulate and air seal at the roof line, which will provide a conditioned or semi-conditioned space for the HVAC equipment. This can improve HVAC performance and longevity as the equipment does not have to work against the much greater temperature differentials of a vented attic.

    For installation guidance for vented and unvented attics in new and existing homes, see these Building America Solution Center guides. For more information, search “attics” or “roofs” in the Solution Center:

    Ensuring Success

    Vented attics are less expensive to insulate and the vents provide for control of condensation in the attic. Unvented attics can provide more resistance against wind pressures and wind-driven rain in high wind regions and protection against wind-borne embers in wildfire-prone areas. They can also provide an insulated space for storage and HVAC equipment. Climate, homeowner desires, and subcontractor skill levels may dictate which option to choose. 

    The key to creating an unvented roof assembly is to keep the roof deck – the principle condensing surface in roof assemblies – sufficiently warm throughout the year such that condensation will not occur, or to prevent moisture-laden air from the interior of the home from accessing the underside of the roof deck. The roof deck can be kept warm by installing rigid foam insulation over the sheathing. For more information on this technique, see the guide Above Deck Rigid Foam Insulation for Existing Roofs. Or, interior moist air can kept from reaching the underside of the roof deck by covering the underside of the roof sheathing with an air-impermeable insulation like closed-cell spray foam.  For more information on this technique, see the guide Below Deck Spray Foam Insulation for Existing Roofs. Both methods require a very high degree of airtightness to avoid condensation. For above-deck rigid foam, air tightness is achieved by installing a continuous membrane over the roof sheathing and under the rigid foam. This membrane could be a peel-and-stick or paint-on membrane or a carefully installed underlayment. For below-deck insulation, the spray foam will provide condensation control. However, all wood-to-wood joints in the framing must still be sealed.

    Climate

    In coastal locations, hurricane regions, and areas prone to wildfires, it may be advisable to construct an unvented attic because soffit vents, roof vents, and gable vents can be entry points for wind-blown rain, burning embers, and salt-laden air that can corrode HVAC and fasteners. If the home is constructed with a vented attic, specify vents that are high wind and fire resistant.

    In hot humid locations, it may also be advisable to construct unvented rather than vented attics to help reduce the entry of moisture-laden air into the attic. In hot humid locations, the outside air is likely to be more humid than the inside air. Inside surfaces may be cooler and may provide condensing surfaces for humid air introduced into a vented attic, thus encouraging condensation in the attic.

    There are climate-specific criteria for attic insulation requirements and impermeable insulation requirements for unvented attics. See the Compliance Tab for specific criteria.

    Right and Wrong Images
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    Right – Button vents provide ventilation to a vented attic
    Right – Button vents provide ventilation to a vented attic
    Image
    Right – A continuous ridge vent provides full ventilation to a vented attic
    Right – A continuous ridge vent provides full ventilation to a vented attic
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    Wrong – Wind-driven rain and wildfire embers can enter an attic through the soffit vents.
    Wrong – Wind-driven rain and wildfire embers can enter an attic through the soffit vents.
    Image
    Right - Baffles are installed in attic to keep blown insulation from blocking soffit vents and ventilation path
    Right - Baffles are installed in attic to keep blown insulation from blocking soffit vents and ventilation path
    Image
    Right – Sheathing extends to rafters adding strength to soffit, baffles keep attic insulation from vent to maintain air flow
    Right – Sheathing extends to rafters adding strength to soffit, baffles keep attic insulation from vent to maintain air flow
    Image
    Wrong – Gable end vents can circumvent soffit-to-ridge airflow and allow in wind-driven rain and wildfire embers
    Wrong – Gable end vents can circumvent soffit-to-ridge airflow and allow in wind-driven rain and wildfire embers
    Image
    Right - A technician applies a thin layer of closed-cell foam to air seal an unvented attic assembly before filling the ceiling joists with batt or blown insulation.
    Right - A technician applies a thin layer of closed-cell foam to air seal an unvented attic assembly before filling the ceiling joists with batt or blown insulation.
    Image
    Right – A continuous ridge vent will be installed along the peak of this roof.
    Right – A continuous ridge vent will be installed along the peak of this roof.
    Image
    Right – Spray foam insulates the unvented attic.
    Right – Spray foam insulates the unvented attic.
    Image
    Right – An insulated space is provided in the home’s attic to house the HVAC equipment.
    Right – An insulated space is provided in the home’s attic to house the HVAC equipment.
    Image
    Spray foam insulates and air seals the ceiling deck and top plates of this vented attic.
    Spray foam insulates and air seals the ceiling deck and top plates of this vented attic.
    Videos
    CAD
    CAD Files
    Thin-profile attic eave baffle and vent
    Thin-profile attic eave baffle and vent
    Download: DWG PDF
    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

    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.

     

    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 402 Building Thermal Envelope. Table 402.1.3 (402.1.2 in 2015/2018 and 402.1.1 in 2009 IECC) 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. The 2021 IECC states that this exception can also be followed when R-60 insulation is required: R-49 insulation is recognized to satisfy the requirement for R-49 insulation when 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 402.2.2 Ceilings without attic spaces. Where the prescriptive requirements would require more than R-30 insulation but the roof/ceiling configuration cannot accommodate the insulation level indicated by the prescriptive requirements, R-30 is the minimum insulation requirement. This reduced insulation requirement is limited to the lesser of 500 square feet or 20% of the total insulated ceiling area.

    Section R402.2.3 Eave baffle. (Not included in the 2009 IECC) 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. The baffle must be installed to the outer edge of the exterior wall tap plate and baffles shall be installed continuously where soffit venting is not continuous.

    Note that baffles should also be used with vented cathedral assemblies.

    Section 402.2.4 (402.2.3 in 2009 IECC) 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.

    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.

     

    2009201220152018, and 2021 International Residential Code (IRC)

    Chapter 3 Building Planning.

    Section R301.2.1 Wind design criteria. Buildings shall be constructed in accordance with the wind provisions of this code using the ultimate design wind speed in Table R301.2(1) as determined from Figure R301.2(5)A. Where not otherwise specified, the wind loads listed in Table R301.2(2) adjusted for height and exposure using Table R301.2(3) shall be used to determine design load performance requirements.

    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.

    Chapter 8 Roof-ceiling construction.

    Section R806 Roof Ventilation. Construction ventilation requirement and provisions for protections against weather, insect and vermin intrusion; also includes minimum vent area, insulation clearance, installation, and rafter assemblies.

    Section R806.3 Vent and insulation clearance. Provisions to prevent insulation from blocking the free flow of air in a ventilated roof assembly. Does not apply where an unvented roof assembly is used as indicated in Section R806.5 (R806.4 IRC 2009).

    Section R806.4 Installation and weather protection. Provisions to install ventilation components in roofs in accordance with both manufacturer’s instructions and Section R903. (IRC 2012-2021 only)

    Section R806.5 Unvented attic assemblies. This section outlines the conditions for unvented attic/roof assemblies. (R806.4 IRC 2009) Note that Table R806.5 (R806.4 IRC 2009) indicates the amount of insulation above the roof deck or air-impermeable insulation below the roof deck required for condensation control assuming minimum required total insulation as indicated in Chapter 11 Energy Efficiency Section N1102 Building Thermal Envelope. Higher R-value assemblies will require a proportionally larger amount of air-impermeable insulation below the roof deck or insulation above the roof deck for condensation control.

    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 R806.4 Unvented attic assemblies. This section outlines the conditions for unvented attic/roof assemblies. Note that table R806.4 indicates the amount of insulation above the roof deck or air-impermeable insulation below the roof deck required for condensation control assuming minimum required total insulation as indicated in Section N1102 Building Thermal Envelope. Higher R-value assemblies will require a proportionally larger amount of air-impermeable insulation below the roof deck or insulation above the roof deck for condensation control.

    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 the specific language of this section for the required dimensions of the access.

    Chapter 11 Energy Efficiency

    Section N1102 Building Thermal Envelope. Table N1102.1 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. The 2021 IRC states that this exception can also be followed when R-60 insulation is required: R-49 insulation is recognized to satisfy the requirement for R-49 insulation when 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 N1102.2.2 Ceilings without attic spaces. Where the prescriptive requirements would require more than R-30 insulation but the roof/ceiling configuration cannot accommodate the insulation level indicated by the prescriptive requirements, R-30 is the minimum insulation requirement. This reduced insulation requirement is limited to the lesser of 500 square feet or 20% of the total insulated ceiling area.

    Section N1102.2.3 Eave baffle. (IRC 2012-2021 only) 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 (Section N1102.2.3 in IRC 2009) 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.

     

    2009, 2012, 2015, 2018, and 2021 International Wildland-Urban Interface Code (IWUIC)

    Chapter 5 Sections 504, 505, and 506 discuss the requirements for roof assemblies in the wildland-urban interface.

    Section 504 Class 1 Ignition-Resistant Construction.

    Section 504.10.1 Attic ventilation openings, foundation or underfloor vents, or other ventilation openings in vertical exterior walls and vents through roofs shall not exceed 144 square inches (0.0929 m2) each. Such vents shall be covered with noncombustible corrosion-resistant mesh with openings not to exceed ¼ inch (6.4 mm), or shall be designed and approved to prevent flame or ember penetration into the structure.

    Section 504.10.1 Vent locations. Attic ventilation openings shall not be located in soffits, in eave overhangs, between rafters at eaves, or in other overhang areas. Gable end and dormer vents shall be located not less than 10 feet (3048 mm) from lot lines. Underfloor ventilation openings shall be located as close to grade as practical.

    Section 505 Class 2 Ignition-Resistant Construction.

    Section 505.10.1 Attic ventilation openings, foundation or underfloor vents, or other ventilation openings in vertical exterior walls and vents through roofs shall not exceed 144 square inches (0.0929 m2) each. Such vents shall be covered with noncombustible corrosion-resistant mesh with openings not to exceed ¼ inch (6.4 mm), or shall be designed and approved to prevent flame or ember penetration into the structure.

    Section 505.10.1 Vent locations. Attic ventilation openings shall not be located in soffits, in eave overhangs, between rafters at eaves, or in other overhang areas. Gable end and dormer vents shall be located not less than 10 feet (3048 mm) from lot lines. Underfloor ventilation openings shall be located as close to grade as practical.

    Note: The IWUIC does not contain any requirements for attic ventilation openings for Class 3 Ignition-Resistant Construction.

     

    2020 Florida Building Code

    Section 1523.6.5.2.13 Ridge vents of metal, plastic or composition material. All ridge vents shall be tested in compliance with TAS 100(A) for wind-driven water infiltration. All ridge ventilators shall be restricted to roof mean height as tested in compliance with TAS 100(A), and they shall be listed in the system manufacturer’s product approval. (See code for additional requirements and exceptions.)

     

    Existing Homes

    Scope

    Consider occupant use, performance, and building geometry factors when determining whether to retrofit an existing attic to provide insulation and air sealing at the roof line rather than the attic floor.

    Description

    In existing homes, attics are typically vented and may or may not have any insulation (See Figure 1). In determining whether or not to seal the attic and insulate it at the roof line, there are several factors to consider. Some of these factors are listed below. These and other considerations are provided in Table 1.

    • Is the roof supported by truss framing? If yes, it can’t be used for living space, which argues for attic floor insulation.
    • Is the HVAC equipment in the attic? If yes, it should be sealed and insulated at the roof line, even if the roof uses truss framing.
    • Are there already rooms in the attic that are used for living space? If yes, then the simplest way to ensure a continuous air and thermal boundary is likely to insulate at the roof line.
    • Is the attic used for a significant amount of storage? If there is a desire to make that space conditioned to protect stored belongings, if moving everything out to air seal and insulate at the attic floor would be a hassle, and/or if insulating at the attic floor would remove storage space, then insulating at the roof line is a better option.
    • Is there a staircase leading to the attic?
    • Is there flooring over the attic floor? If existing flooring is located perpendicular to the ridge and attached to the framing, if may have been installed to resist roof thrust. Consult a structural engineer before removing. Removal would be the best way to adequately air seal the attic floor, so moving the air and thermal boundary to the roof line is the better option.
    • Is there a lot of dust and debris on the attic floor? Hazardous materials must be removed and surfaces must be cleaned, regardless of which option is chosen.
    • Does the attic have a very low slope that limits the ability to adequately air seal, insulate and provide 2 inches of ventilation space above the insulation from the eaves to ridge vents? If yes, then insulating at the roof line may be the better way to ensure adequate R-value.
    This attic is insulated along the ceiling deck and is vented with soffit and ridge vents.
    Figure 1. This attic is insulated along the ceiling deck and is vented with soffit and ridge vents (Source: Courtesy of PNNL). 

     

    Ensuring Success

    Important Health and Safety Prerequisites for High-Performance Enclosure Retrofits

    Changes to the building enclosure will have a significant impact on the dynamics of water, air, vapor, and heat flow within the home. Certain measures should be implemented to ensure that these changing dynamics do not have negative ramifications for health and safety. It is also important to ensure that parts of the building not directly affected by the work are able to support and protect the planned work. Prior to upgrading to the thermal enclosure,

    • Ensure combustion safety for combustion equipment located within the pressure boundary.
    • Remediate any hazardous conditions that will be affected (e.g., exposed or aggravated) by the planned work.
    • Ensure that the roof system provides robust protection from rainwater and ice dams and that proper flashing is in place (might be concurrent with an upgrade if replacing the roof is a part of the planned work).
    • Provide mechanical ventilation if not already provided.

    Combustion Safety

    Provide minimum combustion safety by providing direct-vent sealed-combustion equipment or forced draft equipment (see Direct Vent Equipment). When furnaces, boilers, and water heaters are installed within the home’s pressure boundary, ideally this equipment would be direct-vent sealed-combustion equipment. If existing equipment is not direct-vent sealed-combustion or forced draft, the homeowners must decide whether to

    • Replace equipment with a direct vent or forced draft equipment, or
    • Retrofit forced-draft to existing equipment.

    Hazardous Materials

    Hazardous materials that will be affected by the retrofit work or that may impact the indoor air quality must be remediated and/or removed. Follow applicable laws and industry procedures for the mitigation of hazardous materials. Engage the services of a qualified professional when needed.

    Roof Condition

    Except where a roof replacement is planned, ensure that the existing roof system provides robust protection from rainwater and ice dams (see the guides Step and Kick-Out Flashing at Roof-Wall Intersections and Roof Eaves Sealed with Self-Adhering Membrane in Cold Climates). A structural evaluation may be needed to determine if the roof is capable of supporting expected snow loads above a high R-value attic/roof assembly.

    Ventilation

    Provide mechanical ventilation complying with Section M1507 of the 2012 International Residential Code. Mechanical ventilation may be added concurrent with or as part of the larger attic/roof retrofit project.

    Compliance

    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.

    2012 IECC

    Section R101.4.3 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 R101.4.5 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.

    2012 IRC

    Appendix J, Section 501.6, Ventilation. This 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.

    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)
    Lstiburek
    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)
    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)
    Neuhauser
    Organization(s)
    Building Science Corporation,
    National Renewable Energy Laboratory,
    BSC
    Publication Date
    Description
    Report about a project that examines implementation of advanced retrofit measures in the context of a large-scale weatherization program and the archetypal Chicago, Illinois, brick bungalow.
    Author(s)
    Pettit,
    Neuhauser,
    Gates
    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)
    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.
    *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 Measures
    Building Science-to-Sales Translator

    High-Performance Thermal Enclosure = High-Performance Thermal Enclosure

    High-Performance Thermal Enclosure
    Sales Message

    A high-performance thermal enclosure ensures both high-efficiency and professional installation for all roof, wall, floor, foundation, and window assemblies. What this means to you is less wasted energy along with enhanced comfort, quiet, and durability. Explore the terms below to find sales themes for the various components within the thermal enclosure of a home.

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