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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.

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.

Checklist

This U.S. Department of Energy checklist includes important specifications that can contribute to a complete and quality installation. All work shall comply with these specifications, all relevant codes and standards, and all manufacturer installation instructions. The contractor shall check each box on the checklist below and sign and date at the bottom to certify the work is completed.

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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 and new roofing installed as needed.

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.

Installation: 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 sealant 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.

Installation: 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 (IECC) and with less than 2% gaps, voids, and compression. Note: the insulation value at the gable walls shall meet or exceed 2012 IECC prescriptive requirements for above-grade walls in the home’s location.

All International Residential Code (IRC) 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.

Resilience Recommendations


Two-part closed-cell polyurethane spray foam is recommended 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%.

Since gable end walls are vulnerable to collapse in high-wind events, it is recommended that two-part closed-cell polyurethane spray foam be applied to improve structural performance. Additional guidance on reinforcement can be found in FEMA documentation.

Commissioning


HVAC supply and return air flow to the attic shall be provided at a rate of 1 CFM/50 ft2 of attic floor area. HVAC system capacity shall be increased if needed, especially if increasing the amount of living space.

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 a target ventilation rate based on house size as follows: 50 cfm for up to 1,500 ft2, 70 cfm for 1,501 to 2,500 ft2, and 100 cfm for over 1,500 ft2. If the home has no whole-house ventilation system, or if the existing system does not meet the target ventilation rate, recommendations shall be made to the homeowner to either install a new system or repair the existing system to meet the target ventilation rate.

At the completion of the work, a radon test kit shall be provided to the homeowner with a recommendation to initiate a radon remediation strategy if post-retrofit radon measurements exceed EPA acceptable levels.
Vented to Unvented Attic

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert 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:

Trust Matters: Inform homeowners how your work conforms to this world-class expert guidance. Recommend they visit the DOE website as evidence these are indeed official best practices.

Knowledge Matters: Take advantage of the Building America Solution Center as a resource for becoming an expert on these projects.

Clarity Matters: Tell prospective clients to contrast your expert-recommended best practices with other contractors.

Value Matters: Advise prospective clients to insist other bids also include these checklists to ensure equivalent quality work.

Message Matters: Showcase on your website and marketing materials that your company uses the highest quality best practices specified on HIE Checklists.

Experiences Matter: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images; pre- and post-energy bills; short and long warranties; and simple charts and graphics depicting performance advantages.

Related Guides

Guide:

Pre-Retrofit Assessment of Attics, Ceilings, and Roofs

Description
Information guide describing things to consider in the attic, ceiling, or roof before attempting retrofits of items including HVAC, wiring, or structural systems.
Guide:

Pre-Retrofit Assessment of Hazardous Materials

Description
Information guide describing hazardous materials that may encountered in the home when retrofitting a home, including asbestos, mold, and radon.
Guide:

Unvented Attic Insulation

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

Vented versus Unvented Attic

Description
Guide describing options for insulating and air sealing at either the attic floor or along the roof line in new homes.
Guide:

Below Deck Spray Foam Insulation for Existing Roofs

Description
Guide describing how to add spray foam insulation to the underside of the existing roof deck as part of the conversion of a vented attic to an unvented, insulated attic.

Disclaimer

This content is a work created with funding provided by the United States Department of Energy under Contract no DE-AC05-076RL01830 for the operation of Pacific Northwest National Laboratory. The information and guidance provided by Pacific Northwest National Laboratory (PNNL) in the content are intended solely for educational purposes only and do not constitute formal training or certification. It is provided with the explicit understanding that neither the United States Government nor the United States Department of Energy, nor the Contractor, nor any or their employees, nor any jurisdiction or organization that has cooperated in the development of these materials, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness or any information, apparatus, product, software, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Viewers assumes full responsibility for all actions that they may take from information provided in this content including ensuring the safety, code compliance, and proper functionality of any products they choose to install. Installation and use of such products should be performed in accordance with local regulations and manufacturer instructions.