You’ve probably been in the attic, over the ceiling and under the roof and marveled at the heat in the summer and cold in the winter. The radiant energy bombarding the ceiling is a major input for the air conditioning system to cope with. That attic poses the biggest ongoing costs for homeowners and is responsible for the bulk of the average household’s energy consumption.
A new kind of roof-and-attic system field-tested at the Department of Energy’s Oak Ridge National Laboratory keeps homes cool in summer and prevents heat loss in winter. The design is a multi-seasonal efficiency almost unseen in today’s roof and attic designs.
To build in efficiency the new design is a system that uses controls for radiation, convection and insulation, including a passive ventilation system that pulls air from the eve of the attic into an inclined air space above the roof. Simply put – the roof deck is doubled with an extra air space between that’s vented.
The passive ventilation system pulls air that would have gone into the house up into an inclined air space above the roof so it can be carried up and out. The system 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.
Bill Miller of ORNL’s Building Envelope Group said, “Heat that would have gone into the house is carried up and out. And with a passive ventilation scheme, there are no moving parts, so it’s guaranteed to work.”
The best news is the new roof system design can be retrofitted with almost all roofing products. The heart of the design is a foiled covered polystyrene insulation that fits over and between rafters in new construction or can be attached on top of an existing shingle roof system. Homeowners don’t have to remove old shingles, which saves money.
The current practice for poorly sealed HVAC ducts leaking air conditioned air into an attic, a practice that ORNL estimates costs homeowners $100 to $300 per year, is to seal the attic with spray foam. Attic spray seals can run $8000 and save a few hundred annually.
But the ORNL retrofit system is expected to be cheaper and still come out even from projecting a $2,000 investment and save a hundred dollars or so.
The team is led by Bill Miller of ORNL’s Building Envelope Group and 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” (a PDF file), has been published by the National Roofing Contractors Association.
This a graphic rich paper well worth a download and saving for later reference. (Docx File)
It’s certainly time for a roof design update. As seen in the paper the assaults on home heating and cooling from above are well worth a minor added investment.
Keep this one in mind when a new roof is needed.