Lessons from Builders Adopting High Performance Attics

By David Peery, C.E.M.

Many production home builders in California have adopted high performance attics. Builders recognize that this envelope feature is one of the most effective energy efficiency measures that can also increase occupant comfort. From utility programs that incentive builders to adopt high performance attics, we can share several lessons learned.

Modeling and Plan Review

When opting for below-roof-deck insulation (HPA-B), most cases do not require a radiant barrier under the roof deck. Prior to HPA-B adoption, many builders would use roof sheathing that included a radiant barrier. However, the application of insulation under the roof deck would require it to touch the radiant barrier, in turn eliminating the radiant barrier effectiveness and benefits. Save money by not including radiant barriers where they are not needed. Note that most building departments will still require radiant barriers on gable ends; however, HPA-B does not require insulation on gable ends.

For unvented attics (also known as sealed attics), some building departments are failing inspections if there is a not a visible 1-inch air gap between the entire roof deck and below deck insulation. The California Energy Commission (CEC) compliance manual shows that a 1-inch air gap is only needed adjacent to the vent and cites ICC 806.3: “Where eave or cornice vents are installed, insulation shall not block the free flow of air. A minimum of a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.” Check with your building department for local requirements.

Insulation installation below roof decks can be trickier than vertical insulation installation in walls. Typically, installers use wires or straps below the roof deck to hold the insulation in place. Avoid fasteners that compress insulation batts because they can degrade insulation performance, or opt for a system specifically designed for below-roof-deck installation. Starting January 1, 2020, Quality Installation Insulation (QII) is mandatory under the 2019 energy code, so be sure to apply the QII principles to attic insulation.


Introducing additional insulation in attics poses several sequencing challenges. Consider roof vent installation: if below-deck insulation installation occurs before vent installation, which is typical, the roofers installing the vents must take caution not to damage the insulation below. It is suggested that the insulation installer return to site to clean up the insulation around each roof penetration to ensure its integrity.

Mechanical and ducting may pose difficulties for the insulation installer if the equipment prevents access to the entire roof deck. Consider installing HVAC equipment after below-deck insulation installation. Even then, double check that subsequent HVAC installation has not dislodged the insulation already installed.

Regular and frequent communication is key! Schedule a kickoff and frequent meetings with the project team regarding installation sequencing. Inform mechanical, insulation, and plumbing trades of the new approach, and prepare time in the project schedule to allow for the insulation installer to repair any insulation issues when on site for ceiling/lid insulation installation. Identify up-front whether the roofer or insulation installer will prepare insulation for venting.


New design approaches require new installation techniques, yet many trades are inexperienced with the new techniques. Product and material pricing is higher for newer, advanced products, and builders see few opportunities to pass on these additional costs to homebuyers.

Try engaging the various trades early. Connect with manufacturers to test out products on a small subset of homes to provide installers and builders opportunity to work with product. Enlist a manufacturer’s product knowledge to advise on installation, and create shared sense of responsibility for additional cost, risk, and learning curve to encourage greater adoption of methods and products.

Try engaging homebuyers to incite demand for smarter, more efficient home designs. Educate homeowners on the value of HPA and HPW. Work to adopt materials and messaging to appeal to this value.

In future articles, we will explore some of the lessons learned from adopting high performance walls.