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Vented to Unvented Attic

Converting an attic from vented to unvented can reduce utility costs while improving comfort, indoor air quality, and durability.

Preparation
The attic shall be inspected for water leaks and moisture, structural, or pest damage. A list of all needed repairs shall be provided to the homeowner before air sealing work begins so remediation can be fully addressed as necessary.
If there is active knob-and-tube wiring present in the attic, insulation shall not be installed until the wiring is replaced with modern wiring. If the knob and tube wiring will remain, it should be properly boxed and it must remain accessible. If the wiring is in the way of properly air sealing and insulating the underside of the roof deck, then it must be moved.
Work shall not proceed if existing insulation is vermiculite, which may contain asbestos.
If there is a vapor retarder on the attic floor, it shall be removed to allow any moisture that builds up in an unvented attic to diffuse into the house below.
All openings that exist to ventilate the attic, including ridge vents, gable vents, and soffit vents shall be closed off and sealed with reroofing work as necessary.
All wood-to-wood framing joints and penetrations exposed to exterior conditions shall be sealed.
Any existing whole-house fan shall be removed or disabled and the drywall ceiling opening shall be fully patched and refinished to match the existing ceiling.
Care shall be taken not to block, remove, or disable kitchen or bathroom fan exhaust vents, water heater or furnace flues, radon vent pipes, and plumbing vent pipes. All kitchen or bath exhaust fans shall be modified as required to vent to the outside, not into the attic.
If possible, two-part closed-cell polyurethane spray foam should be installed at all points where roof decking meets rafters and at seams in the roof deck because this can increase the ability of the roof to resist uplift from high winds by up to 300%.
Air Sealing Roof Sheathing and Gable Walls
All sealants used shall be compatible with their intended surfaces and meet fire rating requirements around flues. Maximum gap dimensions shall be consistent with manufacturer’s specifications.
A continuous seal consisting of sprayer-applied caulk, liquid membrane coating, mastic, spray foam, and/or equivalent shall be applied at seams, cracks, joints, and edges, and around all penetrations and vents at all roof sheathing and vertical gable walls to the exterior. Gable end walls are vulnerable to collapse in high-wind events. Applying two-part closed-cell polyurethane spray foam may improve structural performance. Additional guidance on reinforcement can be found in FEMA documentation.
Insulating the Sloped Roof and Gable Walls
Insulation shall be installed at all roof surfaces and gable wall surfaces adjoining the exterior at levels that meet or exceed prescriptive levels specified by the 2012 International Energy Conservation Code and with less than 2% gaps, voids, and compressions. Note: the insulation value at the gable walls shall be the same minimum as required by code for above-grade walls.
All IRC code requirements for air-permeable and air-impermeable insulation at the roof sheathing shall be fully met.
All IRC code requirements for a fire ignition barrier at the insulation surface exposed to the attic shall be fully met.
Commissioning
HVAC supply and return air flow to the attic shall be properly sized. Add HVAC system capacity if needed, especially if increasing the amount of living space.
After completion, a combustion safety test shall be performed if any natural draft combustion equipment exists in the home to ensure there is no back-drafting or spillage of combustion emissions.
The home shall be inspected for the presence of a whole-house ventilation system. If one is present, the actual air flow shall be tested and verified to meet ASHRAE 62.2, including the additional square footage of the now unvented attic. If the home has no whole-house ventilation system, or if the existing system does not meet the ASHRAE 62.2 requirements, a recommendation shall be made to the homeowner to either install a new system or repair an existing system to be ASHRAE 62.2-compliant.
In U.S. Environmental Protection Agency Radon Zone 1, a radon test kit shall be provided to the homeowner at the completion of the work so a radon remediation strategy can be undertaken where measurements exceed EPA acceptable levels.

BASC Guides

Information guide describing how to assess attics, ceilings and roofs before proceeding with upgrades in existing homes.


Information guide describing pre-retrofit actions to take to assess for asbestos, volatile organic comounds (VOCs) soil gasses including radon and lead.

Guide describing methods for insulating an unvented attic along the roof line.

Guide describing options for designing/locating the thermal boundary in new and existing homes.

Guide describing how to add spray foam insulation to the underside of the existing roof deck.

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert (HIE) is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

  • Be the Expert: Take advantage of Building America Solution Center comprehensive guidance on ‘Existing Home’ retrofits.
  • Earn Trust: Inform homeowners how your work conforms to U.S. Department of Energy (DOE) world-class expert guidance and recommend homeowners visit the DOE website as evidence these are indeed official best practices.
  • Clarity with Contrast: Tell prospective homeowner clients to compare your expert recommended best practices with other contractors.
  • Ensure Equivalent Pricing: Tell prospective homeowner clients to insist other bids also include DOE checklists to ensure equivalent quality work.
  • Translate Value: Note your company uses DOE HIE Checklists based on world-class expert recommendations for home improvements on all your public-facing communication including websites, advertising, and signage.
  • Create Emotional Experiences: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images for good and bad insulation and air sealing; pre- and post-energy bills following quality installed work; short and long warranties for standard and high-efficiency equipment; and charts showing amounts of contaminants in homes that can be reduced with effective fresh air systems.

Vented to Unvented Attic Background

Applying a spray sealant to an attic

An unvented attic is air sealed and insulated at the sloped roofline instead of at the attic floor. As a result, the attic becomes part of the conditioned space of the home. This protects heating and cooling equipment and ductwork located in attic from temperature extremes so it will last longer and operate more efficiently. An unvented attic also helps reduce potential moisture problems by keeping out humid outside air and wind-driven rain. As an added benefit, the conditioned attic can provide climate-controlled storage space or could potentially be converted to bonus living space if the structural support is in place.