Cost- and Energy-Efficient Attic Designs for California Homes

New attic designs that mimic ducts in the conditioned space have the potential to reduce energy in homes at costs competitive to existing practices.

BIRA Energy


Stockton, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

The recipient instrumented three existing homes in the City of Rio Vista with the following attic approaches: Vented with R-38 on the ceiling, Sealed with box netted R-38 under roof deck, and vented with R-38 on the ceiling and R-19 under roof deck. The monitoring started in August 2018. Unfortunately, the grant expired on June 30, 2018. The Energy Commission staff and the recipient are exploring options for obtaining the monitored data and results for the homes and concluding the project.

The Issue

In 2013, new California home construction totaled 85,310 units; 36,878 single family units and 48,432 multifamily units. An estimated 90% of the single family homes had the heating, ventilation and air conditioning (HVAC) equipment and ductwork (ducts) in the temperature extremes of ventilated attics. California homes place the HVAC and ducts in the attic to avoid using valuable living space. Placing ducts in the attic makes duct installations easier and less expensive. However, this practice results in wasted energy estimated at about 4.8 TWh and significant carbon emissions estimated at 1.2 million metric tons of equivalent carbon dioxide emissions (CO2e) each year.

Project Innovation

This project evaluates, tests and refines two different attic designs in California homes, and recommends the best approaches to home builders addressing cost-effectiveness and energy-efficiency. The baseline will be the current energy efficiency code practices for ventilated roof attics with no additional attic insulation and ducts within the attic that comply with the current energy code (2013) requirements for ducting.

Project Benefits

Methods to improve the efficiency of building envelopes have included sealed, insulated attics as well as standard vented attics but are in limited use in the market today. However, these approaches add considerable cost to builders under current practices. The research team is employing new and novel installation methods and materials, which include low cost fiberglass insulation with boxed netting and integral vapor retarder, that have the potential for energy savings on par with ducts in the conditioned space, but at a cost similar to current construction practices.

Lower Costs


The project could lower energy cost to ratepayers by developing attic assemblies that allow ducts to perform as if they were located in the "conditioned space" and reduce HVAC energy costs without adding cost to builders. Pilot work on the attic designs have demonstrated that these approaches can potentially be cost neutral to ratepayers. Assuming a market penetration of 73% of the current single-family market, new construction with these designs could potentially recoup the costs to ratepayers within a single year.

Key Project Members

Project Member

Robert Hammon




Electric Power Research Institute, Inc.


Oak Ridge National Laboratory


Oak Ridge Associated Universities


Michael L Dalton, CPA




Match Partners


Owens Corning


Contact the Team