ORNL roof-and-attic system keeps houses cool in summer, warm in winter
The new roof system includes controls for radiation, convection and insulation, and a passive ventilation system
Heating and cooling a house are two of the biggest ongoing costs for homeowners and are responsible for the bulk of the average household’s energy consumption. A new kind of roof-and-attic system field tested at the DoE’s Oak Ridge National Laboratory (ORNL) improves the efficiency of both winter heating and summer cooling. Importantly, the new system can be retrofitted to most existing roofs.
The new roof system design includes a passive ventilation system that pulls air that would have gone into the house from the underbelly of the attic, up into an inclined air space above the roof so it can be carried up and out. It also features controls for radiation, convection and a foiled covered polystyrene insulation. This insulation forms the heart of the system and can be fitted over and between rafters in new constructions or attached on top of an existing shingle roof system without the need to remove the old shingles.
The ORNL team says computer simulations show that poorly sealed heating, ventilation, and air conditioning (HVAC) ducts that leak conditioned air into an attic typically cost homeowners US$100 to $300 per year. Sealing the attic with spray foam can save over $460 a year, but the initial cost is around $8,000.
In comparison, ORNL claims retrofitting the new roof-and-attic design to an existing house could save homeowners around $100 a year, but for an initial cost of about $2,000. While the yearly savings aren’t as high, the significantly lower initial cost would result in close to the same number of payback years for both approaches.
The team, led by Bill Miller of ORNL's Building Envelope Group, is working on designs that would lower initial installation costs even further to provide greater overall cost effectiveness.
The team’s paper, “Prototype Roof Deck Designed to Self-Regulate Deck Temperature and Reduce Heat Transfer” (PDF), was published by the National Roofing Contractors Association.
About the Author
Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.
All articles by Darren Quick
I put a roof exactly like this on my house about 12 years ago. It's called an "ice house" roof because this construction was used (before the advent of home based refrigeration) to build structures for storing ice between visits from the iceman. The concept is sound and works well. On new construction the cost impact would be minimal. In my case it was a hail damage re-roof and the cost/benefit equation was occluded by insurance claims and the fact that I upgraded my air conditioning equipment at about the same time. I can say, however, that our monthly AC cost went down year over year after we added the ice house roof.
Amhome of Florida and HCI, the company that now has the patents have built this type of roof for over 20 years but use 8-7/8 inch thick polystyrene foam below foil backed roof decking leaving an 1-1/2 inch air gap for air flow from ventilated soffitts to ridge vents, creating an R-50 rated roof system.
Sorry, this is NOT news ORNL.
My 70’s home has been upgraded using off-the-shelf products that have been available for decades. We increase the soffit venting and put in rafter baffles up to the peak from the vent along the underside of the roof deck. Aluminum foil was fastened to the underside of the rafter behind the baffles. This created the air-flow and heat reflectance to the roof.
Additional peak venting was made and a decorative gable vent and exhaust fan was added powered by a solar panel. The R-30 in the attic floor joists was over-laid with R-30 batts rolled across the joist creating a thermal break with the joist to the attic. This was over-laid with a commercial perforated foil product to increase infra-red reflectance back into the attic. The heating and air conditioning use plummeted to half of previous use. The total cost was far less than expected and should have a 7.5-year pay-back.
Tell me again why this ORNL design is getting news?
Keeping the roofs fit and cool in summers is a big challenge for most of the homeowners. As the temperature raises cost of cooling the house obviously increases. In summers you can paint your roofs with white color or with specially formulated reflective paint as it will help rooms under the flat roofs much cooler.
Over 160,000 people receive our email newsletter
See the stories that matter in your inbox every morning