ORNL roof and attic design proves efficient in summer and winter
A new roof system field-tested at Oak Ridge National Laboratory improves efficiency using controls for radiation, convection and insulation, including a passive ventilation system that pulls air from the underbelly of the attic into an inclined air space above the roof.
OAK RIDGE, Tenn., Sep. 10, 2012 — 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, a multi-seasonal efficiency uncommon in roof and attic design.
The system improves efficiency using controls for radiation, convection and insulation, including a passive ventilation system that pulls air from the underbelly of the attic into an inclined air space above the roof.
“Heat that would have gone into the house is carried up and out,” says Bill Miller of ORNL’s Building Envelope Group. “And with a passive ventilation scheme, there are no moving parts, so it’s guaranteed to work.”
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.
Poorly sealed HVAC ducts leak conditioned air into an attic, which typically costs homeowners $100 to $300 per year based on ORNL computer simulations.
To address the problem, some homeowners pay $8,000 to seal the attic with spray foam, which can save upwards of $460 a year. For less initial cost and the same number of payback years, homeowners can retrofit the attic with the new design for about $2,000 and save $100 a year.
Looking to the future, Miller and colleagues are working on designs with lower initial installation costs, and greater cost-effectiveness overall.
The paper, “Prototype Roof Deck Designed to Self-Regulate Deck Temperature and Reduce Heat Transfer,” was published by the National Roofing Contractors Association. Authors on the paper are W. Miller, Stan Atherton and Russell Graves of the University of Tennessee, Knoxville, and Billy Ellis of Billy Ellis Roofing.
Funding was provided by the DOE Office of Energy Efficiency and Renewable Energy and Billy Ellis Roofing under a User Agreement. UT-Battelle manages ORNL for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.
UT-Battelle manages ORNL for the Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.
Is this more efficient that a properly placed deciduous tree?
For those of us in the temperate climate zone, it looks like the major problem would be finding a contractor who has a clue as to how to implement that concept.
I’ve no idea if this works, but it is advertised in a lot of English language publications (here in Limousin, France) as a way of keeping holiday homes ventilated when they are unoccupied, particularly over winter.
http://www.solarventi.com/generelt/generelt.htm
QUOTE: Does this make sense to anyone? I don’t see why anyone would spend $8K to seal the attic and essentially air condition it. Why not fix the leaking ducts?
It’s becoming popular to seal and condition the attic. Otherwise you get humidity inside the attic that moves through the fiberglass insulation and condenses on the ductwork, causing mold. The attic doesn’t get conditioned much though.
In our house the ductwork runs in the basement, so any leaks just condition the partly finished space down there.
In our last house we had a similar functioning roof. We had a metal roof installed over the shingle roof, on purlins. So there was a 3/4 inch (2cm) gap between the metal and the shingle. The air would heat up, and move through the vertical ridges (bumps in the roof material) to the ridge. I don’t think it made a huge difference, but everything helps.
Pittzer @ur momisugly 9/12 2:50 PM
I did roofing (and genrall house work) from about 2003 to 2008. The current ‘best’ in terms of cost/effectiveness is to do ridge venting with soffet venting. Also including roof ducts under then decking can help. The reason for this is most heat in the attic is trapped rising heat combined with radiated external. Obviously if the house AC is 70 and the outside is 90, then there isn’t much rising heat, but a lot of solar heating. Proper venting (keeping the attic cool) is important to increase the longevity of the shingles. Shingles being REQUIRED in certian areas – notably Florida doesn’t alow metal or tile roofs. (shingles can be ‘glued’ down better than the other types and are less likely to blow off in huricanes).
Notes- soffet vent – soffet is the area of the house under the roof that makes up the ‘eves’. It is parell to the ground. If it were inside it would be a ‘ceiling’. Roof duct is generally a styrofoam chute about 3 feet long 12 wide and 3 inches ‘deep’. These are made by Owens Corning (possibly others – see http://www.[favorite home improvement].com [search roofing] and it should come up). Used at the bottom of the roof going up into the attic space, this alows the soffet vent air flow to go up along the inside of the roof, alowing for ideally the temp in the attic to cool down to the temp outside.
I hope that helps.
I’m thinking that in Texas at least, garage doors should have vents in them and a ceiling vent pipe in the garage connected to a solar powered exhaust fan. My garage gets pretty hot. I’ve even heard of HOAs that forbid keeping your garage door open which would keep the garage cooler during the day when you are home.
Solar powered fans don’t really work. Not enough power from the tiny collectors to power a real fan. Those spinning turbines don’t do anything at all. Continuous ridge vent with adequate sofffet is the best. Powered gable fans work too.
For your garage, you could check and see if there is insulation in the attic over it. If not, put some in.
This is similar to how I insulated the attic over my garage. I bought a bunch of Mylar “space blankets” and stapled them to the 2×6 rafters. Heat is channeled up to the ridge vent. Cost me about $50 and it works fabulously.
phillip bradley:
about shutting off the roof ventilator (rotary type) for winter.
every labor day slip up there with a suitably size trash bag and some bungee cords, place the bag over the turbine and tie it down with the bungees. then next spring take it off.
even seventy year olds can do that.
C
Unlike measuring temperature, the best solution in roof design is location dependent. What is best in hot and humid is not the same in cold and wet. Even the prevailing winds can make a difference (well duh). Secretary Chu’s white roof campaign suffers from the same bureaucratic “one size fits all” solution (and a whole lot more). It also fails to recognize seasonal changes (though who still puts up storm windows each spring and fall anymore).
As an architect with over 30 years experience, I don’t trust the model output, numbers or lack of unexpected problems. I see some possible benefits which might actually work in TN. I also see fire marshals having a cow over potential chimney effect of such a ventilated roof/attic. Fire concerns were the real reason for the failure of double wall construction to achieve much market penetration.
Does someone know how to make a roof white, black or grey at the push of a button?
Please let me know if you have ideas to accomplish this. Thanks.
Until then, foam roofing is probably the way to go, Les Johnson’s idea looks really good too for hot and cold places. Most of the USA is both hot and cold, right?
Poems of Our Climate says:
September 13, 2012 at 9:40 pm
Does someone know how to make a roof white, black or grey at the push of a button?
Use LCD tv screens for the tiles!
Don’t we have an engineer who has been to Sardinia and can describe the mechanics of the the typical roof in that country? Vents built into the wall from a foot or two above the floor, leading to a vented ridge attic. They work magnificently in the summer but my guess would be that one would need to plug the wall vents in winter. The Sardinians have been building them for centuries.