For purposes of the study, an under-insulated was defined as one that doesn’t meet the 2012 International Energy Conservation Code (IECC). The 2012 IECC was selected because it has been widely adopted and leads to easily achievable levels of envelope efficiency, a press release from NAIMA said. Twenty-two of the 50 U.S. 50 states have adopted an energy code equivalent to or more stringent than the 2012 IECC.

Using the National Renewable Energy Laboratory (NREL) 2024 ResStock database, ICF extrapolated a sample of 1 million homes for the study. The homes were representative of the construction in all U.S. climate zones and regions, with varied ages, geographic locations, foundation types, and geometries, the NAIMA press release said.

“This research underscores the need to retrofit homes with air sealing and insulation, since almost nine out of 10 homes are under-insulated,” said Curt Rich, president and CEO of NAIMA. “The good news is that homeowners can now take advantage of the 25C tax credit to conduct insulation retrofit work. The tax credit is worth $1,200 and can be claimed every year through 2032. There has never been a better time for homeowners to make their homes more comfortable and lower their utility costs by re-insulating their attic.”

“Poorly insulated homes cause high energy bills, uncomfortable temperatures, and needless damage to our climate from wasted energy,” said Steve Nadel, executive director of the American Council for an Energy-Efficient Economy. “This report shows that under-insulated homes are unfortunately not a rare occurrence but rather the norm. Our policymakers should redouble efforts to help residents better insulate their homes and ensure brand-new homes are built with proper insulation from the start.”

Click here to access the ICF report.