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/.
MarkW says:
September 12, 2012 at 3:27 pm
I’d love to know how much this would add to the cost of a new roof.
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From the looks of it, I would think for new construction, it would add little to the cost.
Not an engineer here, but combining a design like that along with a concept I’ve played with in the idea stage, might do a lot for energy use. The concept I’ve played with is sort of a simplified low-tech geothermal idea for individual dwellings that also addresses the desire for decent ventilation levels. Basically you run radiating/reverse-radiating pipes through the ground and pump air into the house with simply fan power after it runs through the pipes: the air being pumped in will tend to be warmed by the ground in the winter and cooled by the ground in the summer: instead of hot or cold air wisping into and out of the house randomly through vents and cracks there’s a constant supply of fresh air at a “better than outside” temperature constantly being pumped into a slightly-over-pressured home.
Hey, seems like a decent idea… but like I say, I ain’t a injineer!
:>
MJM
“homeowners can retrofit the attic with the new design for about $2,000 and save $100 a year.”
20 years to break even not counting a return on an alternate investment. No thanks.
As mentioned above, double roofs are very effective in tropical Australia, but here is a design from the UK for offices that, to me are very attractive, and a design like this may be a good promotional tool if ‘eco’ is part of your business model.
This is not a ‘new’ design, so there should be no concerns about someone trying to patent it.
My house roof incorporates a roof identical to this and was built in 1990-91. The design was a standard feature of the EXN modular system developed by Réunion Island architect Maurice Tomi. The system became popular after a Category 4 hit Réunion and in many places only Tomi’s buildings were left standing.
Our place didn’t move, didn’t even ‘sing’ in a 200km/hr wind last year.
The system incorporates ‘umbrella’ framing, steel-cored columns with an F28 grade cruciform hardwood stud surround, and hardwood girder trusses. Renders internal walls non load-bearing and therefore optional.
Maurice’s design is a bit expensive to build these days. I have subsequently built two dwellings that have the same type of roof & ceiling using cold-formed steel portal frame.
Good intent, but there are better and cheaper ways to accomplish the same purpose!
This is overly complex and costly and their cost estimate is not even close. $2,000 would not cover the material cost of any one of those three extra layers. Who pays (or charges) $8,000 to seal ductwork? Seems to be 10x the real cost.
What world do these people live in? It is not one I recognize as a practicing architect and builder.
That press release caught my eye yesterday. I contacted the lead author, Bill Miller, who very kindly sent me a PDF of the paper. There’s a lot of good information in it beyond the roof design, including data on energy savings based on HVAC ductwork placement and insulation. I knew about the efficiency differences, but the quantified numbers were pretty amazing. (Yeah, that part is based on a model, but it’s a standardized model that gets tested against the real world.)
This particular roof design is of more value in hot climes than cold, but the contractor they were working with _is_ based in Texas. And the concept has been around for a while (as in Amerindian tipis with liner), but there are some interesting refinements. The PR graphic doesn’t make it completely clear, but this is more than just eave vents. It’s a combination of insulation and a second convection path _above_ the deck (it does work _with_ the eave vents, though). I was favorably impressed, and I don’t generally automatically go for all the latest neato “green” stuff.
Curiousgeorge: The paper does address load-bearing issues and admits that the new deck retrofit isn’t always going to work. I think it’s going to be most useful in new construction, or when the old roof deck needs to be removed anyway due to damage.
can i get a plug for my roof idea?
Very interesting. I’ll bet it would especially help to avoid ice dams. Could pose a problem with squirrels and birds, though; looks like a nice narrow inaccessible channel, just right for nesting without possible disturbance by humans.
A few houses here in Spokane are built with a different type of air-flow setup that appears to accomplish the same purpose…
(Screencap from Google streetview):
http://ockhamsbungalow.com/blog34/roof-isolation.jpg
And how is this really any different than tacking foil insulation (or foiled foam) underneath the rafters? Basically, they’re jsut trying to make sure that hot air stays in the channel, a hot roof reflects back out instead of coming into the attic (summer) and that in winter there is a semi-conditioned attic space where any heat gets reflected back inside rather than hitting the cold cold roof.
Not seeing the real innovation here… I’ve basically done something similar to half my house (have to finish one day.)
My grandfather was building houses with soffit and ridge vents back when they dug basements with horse-pulled dredges. If he’d stretched some radiant barrier foil (currently 13 cents a sq ft) across the rafters, he’d have the same efficiency as this ‘new’ system.
Anyone remember the ‘envelope’ house, with double walls and an air space between? That went nowhere because you were essentially building two houses, one inside the other. Double roof decks, why didn’t we think of this before?
ORNL needs to get back to building nukes.
Way to go Oak Ridge…
Way to rediscover something only a couple hundred years old… you can see this in barn construction from a long long time ago.
Not really new; just new to new researchers in the filed who aren’t well versed in the history of such things.
There are efficient roof design houses up in the snow fields around lake Tahoe. You start with a South facing glass wall (not in Australasia) atrium with a vented floor leading to under house rock piles, like scoria full of air pockets. The roof is near flat sloping from south to north downwards at a slight angle, and a 6-12 inch gap between the to roof layers, and down the north wall, that leads back down to the subterranium.
Sun in the day heats the air in the Atrium, and it goes up over the roof, and then down in the cellar to heat up the rocks, and keeps your tropical garden in the Atrium percolating. At night the warm air in the basement at the north end rises back up the wall, and over the roof keeping it warm, and then once cooled it drops back down in the Atrium, just as it does in the tropical rainforest nights. Works so well, that such houses have been built up there with NO auxilliary heating like a pot belly stove. First guy who built one was forced by the loan company, to put in such a stove auxilliary; but it never ever got used, so they dropped the requirement for newer homes.
But you do lose quite a few cubic feet with such systems.
Where we live at 2500 meters in the Colorado front range the diurnal variation is typically 20c or more . We never need air conditioning . A few years ago we finally put in a ( dog proof ) screen door to harvest some of the summertime afternoon heat . I’ve thought of checking out the feasibility of harvesting the daytime heating of the attic air with just a few vents and simple fan to blow the warmed air down into the living area whenever the attic air was warmer .
I think some of the biggest returns can be made with quite simple technologies .
So the scientists have finally caught up with the tent fly.
michaeljmcfadden says: September 12, 2012 at 5:01 pm
Basically you run radiating/reverse-radiating pipes through the ground and pump air into the house with simply fan power after it runs through the pipes: the air being pumped in will tend to be warmed by the ground in the winter and cooled by the ground in the summer: instead of hot or cold air wisping into and out of the house randomly through vents and cracks there’s a constant supply of fresh air at a “better than outside” temperature constantly being pumped into a slightly-over-pressured home.
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That sounds an awful lot like a low-tech system used on the plains in the days of yore, that my dad told me about just the other day. A deep, covered trench would extend away from the house, leading to a vent under the floor. Combined with a vent in the roof, convection would pull the cooler air from the ground into the house. Things like this, breezeways, sod roofs, and dugouts would have made a degree of comfort in these climes impossible with our current building techniques.
The article says it can be installed over an existing roof (4th paragraph).
My design is similar, but easier and cheaper to retrofit.
1. Putting mylar on the inside of the roof rafters. The mylar would down, go to just above the sofits. This will tend to draw cooler outside air directly into the gap above the mylar. At the top of the roof, near the gable, mylar would go across to the opposite rafters, about 1-2 ft down from the gable top. If there is cross bracing, the myalr would follow the braces. This space allows all channels between the rafters to be interconnected.
2. Installing solar powered, temperature controlled fans, at least 2. One would pull air from the gap between the mylar and the roof deck. The other would pull air from the rest of the attic. There are also conventional vents, which would work in passive mode.
In the Texas winter, the fans are set to pull air only if the attic temps goes above 80 deg F.
In the summer, I disable this, and the fans run as long as there is sunlight, and for 10 minutes every hour when there is insufficient sun (from house power).
I paid just under 1000 for the fans. The mylar (not yet installed) will cost a few hundred.
The mylar will insulate the larger attic from external heat, and will keep winter heat in. The system will also work in passive mode.
It’s suitable to aplied in tropical country like Indonesia
So convection is used to cool the roof because radiation does not cool the roof.
This post is giving me a sense of deja vu. I seem to remember commenting before on a similar thread that it was like the ‘safari roof’ on a Land Rover.
My 300+ years old house has such a roof. Since when it was build. The more things change…..
gee, I should do a paper on my house. It’s quite similar and is about 10 yrs in operation. It has R30 insulation on the ceiling, radiant barrier (foil covered material for radiant barrier) on the rafters under the roof with venting under the roof deck going up to a ridge vent and also down to the top of the wall which has a 3/4 air gap providing a chimney between the radiant barrier inside the inner wall and the outer wall in what is called vent skinning. Air travels (is drawn) up the sides of the house, into the attic, and up and out the ridge vent. There are also vents underneath the rafters at the eaves on the ends. Additionally, all AC / heating equipment, ducts and vents are located in the living space so there is no heat gain or loss with the attic. When our AC unit failed last month, we noticed it when the temperature hit 81 deg F in the early morning and by the time the repairman arrived around noon, the temperature inside had risen to 82 deg F. Living in the S TX, the early morning temperature was above 82 deg F and by noon it was pushing towards 100 deg F. Note the AC is typically run 12 months during the year, just not as much during our typical 2 weeks of winter and 6 weeks of spring and fall.
I wonder if their next gov. grant will get them to the point of vent skinning where the walls become a part of the natural venting and cooling system.
I agree with george e smith that this is not new technology or technique. A two story commercial/institutional building near where I work is having a similar design being installed on two new ell additions.
The steel trusses were covered in steel sheathing which had foam sheets go over it. Wood furring strips were then mounted on the foam to which plywood sheathing was nailed. Then rubber ice dam seals at the eaves and valleys, all topped with what appears to be a tar paper-fabric combo with asphalt shingles capping it out. There appears to be ridge venting, and like the original structure, the ells also have dormer vents. A mix of old and very old building techniques.
Rocket science! Just as when you put a first roof layer over a vented air space you get some insulation and convection protection from the outside, when you add a second roof layer with an additional vented air space to the mix, you get more protection from the outside conditions.
Next breaking headline: “When you add a third roof layer with an additional vented air space, you get a little more protection from outside conditions.”
And, I’m sure that next nugget of rocket science will cost more $tens of millions.
Geeze. No wonder we’re going broke.