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.