Comparing Attic Approaches for Zero Net Energy Homes

Energy and Cost Saving Attic Approaches for Homes

Lawrence Berkeley National Laboratory


Berkeley, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

Staff is reviewing the final report and a final project presentation occurred on 12/19/18. The Fresno test home was monitored continuously from September 2016 to the end of April 2018, and the Clovis test home was monitored from June 2017 through mid-May 2018. The Fresno home exceeds California Title 24 energy performance requirements by 30%, while the Clovis home is designed as a net zero-energy home. Over 100 sensors were installed per home, monitoring temperature, relative humidity, heat flux, surface condensation, moisture and HVAC energy use. An improved version of a sophisticated and mature model called Register Capacity (REGCAP) was used to extend results to all of California's 16 climate zones. Preliminary results indicate an average of 18 percent savings in HVAC energy use using these approaches.

The Issue

As homes approach zero net energy (ZNE), the energy impacts of some emerging construction strategies need investigation to determine their energy impacts. One strategy is to seal and insulate the attic that contains the home's thermal distribution system. However, there are questions regarding the level of air sealing and insulation needed, the impact on attic humidity and potential for attic or roof damage, and the overall impact on annual building energy use.

Project Innovation

The project focused on the performance of different attic assemblies and their associated heating, ventilating and air conditioning (HVAC) systems. Field measurements of attic and HVAC system performance were conducted in two new high performance homes in California with sealed and insulated attics. One home was built to be about 30 percent better than Title 24 and the other is a ZNE home. The attic insulation approach involved a new lower-cost approach using blown insulation that does not use expensive spray-foam. The results of the measurements are used directly to provide technical support for potential changes to Title 24 and provide information to contractors and builders on sealed and insulated attic performance and alternative approaches.

Project Goals

Assess the thermal conditions in sealed and insulted attics and predict HVAC energy savings across new California homes.
Evaluate moisture performance for sealed attics using vapor permeable insulation to identify moisture risks.
Identify potential solutions to moisture issues in sealed attics.

Project Benefits

This project will lead to technological advancement by offering alternative construction techniques for sealing and insulating attics, compared to conventional methods. The alternative technique involves the use of sealed attics and could lead to electricity savings and peak demand savings when compared to conventional duct systems, and also increase occupant comfort. The recipient is working with building developers on these new techniques which will contribute to achieving ZNE goals for new construction. The techniques can also be applied to home retrofits with HVAC equipment.

Lower Costs


The technologies and construction techniques could result in significant reduction in heating and cooling energy cost which is estimated to be 15 percent for new construction and 25 percent for retrofits.

Environmental & Public Health

Environmental Sustainability

A 15 percent reduction in energy use associated with unvented attics could result in reductions in greenhouse gas emissions. Assuming 10 percent of new homes are built with the attic approaches recommended in this study, approximately 5,000 metric ton of CO2e will be reduced compared to standard construction.

Key Project Members

Iain Walker

Iain Walker

Brennan Less

Brennan Less

Senior Scientific Engineering Associate



De Young Properties


Contact the Team