Something practical – new roof design saves energy

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.

By Emma Macmillan

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/.

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63 Responses to Something practical – new roof design saves energy

  1. In Sweden keeping heat in during winter is the main problem, not keeping heat out. Good insulation could become useful summertime too. Latest summer was the worst for ages, with only half a dozen “real summerdays” local weather service says.

    –Ahrvid

    Ps. Hackers hacking away at Jo Nova again? It this moment I only get “This account has been suspended” when trying to connect.

  2. EternalOptimist says:

    Brilliant
    Saving energy is good. It’s what I believed since I was 20 years old.
    just leave the carbon, the politics, the tree rings, Al Gore, Mann, Gleik and the Polar bears out of it.
    and let me go back to growing potatoes and other stuff

    and Hansen.Please no more Hansen

  3. Long time reader, and very occasional poster. Had to comment on this as it is not totally new, just a variation on a ventilated ridge system.

    My house in rural Australia has a large verandah completely surrounding the house. Under the verandah, all the way around is a vent feeding into the cavity between insulation and the corrugated steel roof. All along the ridge of the roof is a ventilation cowling. Cooler air is drawn in from the vent under the verandah, and convects up the underside of the roofing, venting out at the top.

    It’s effectiveness is clear inside the house on 100 degree plus days, and of course the fact that it requires regular cleaning of dust buildup from the mesh covering the inlet vent!

    Something old is new again!

  4. I seem to remember this passive double-layer roof ventilation system from my years in southern Spain. Not quite as sophisticated, of course, and executed in concrete, but I think the basic idea is the same.

  5. eyesonu says:

    This is not brain surgery. It’s common sense.

    Now will someone be getting a patent on the “new” idea? I hope not.

  6. Curiousgeorge says:

    I seriously doubt it could be done for the cost they estimate on any but the smallest of homes with plain roofs. Maybe a 1000sqft house could be done for $2000. You can’t even get asphalt shingles replaced on a standard 1800sqft house for under $5000. And I’d want a engineering evaluation of the additional weight and resulting stresses during a heavy snow. Btw, this design would not shed snow very well without additional heat being added somehow.

  7. Steve says:

    Have they tested this in heavy snow climes?

  8. Sean says:

    Why does the green cult not spend some of their billions on developing useful energy efficient suggestions like this instead of wasting it like they do on activism, propaganda and hate speech?

  9. ntesdorf says:

    As Tim Wainwright says this sort of roof design is common in Australia and has been so for 100 years especially in the tropics, Our own house in Sydney has solar panels on the north (sunny) slope and they act as a cooling sub0surface airflow channel which keeps the house 10 degrees cooler in hot weather in addition to the effects of 6 inch roof insulation and 6 inch sub attic floor insulation. We do not seem to have much in the way of winters in Sydney but summers used to be very hot.
    It is good to see people devoting themselves to practical cost-saving ideas that are useful to peoplerather than pursuing anti-social scams like CAGW and Carbon trading.

  10. Pittzer says:

    Quote: 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./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?

    This solution seem more about moving hot air out of an attic to keep it from radiating heat back into the living area of the home. I’m very interested because I am about to begin the design phase on a new home.

  11. Sean says:

    just checked Jo Nova – also getting the account suspended message…

  12. Matthew W says:

    Pittzer says:
    September 12, 2012 at 2:50 pm
    Does this make sense to anyone? I don’t see why anyone would spend $8K to seal the attic and essentially air condition it.
    ===========================================================
    Yes it does make sense.
    Think “GOVERNMENT SUBSIDIES” via stimulus spending.
    (remember the insulation boondoggle associated with the last porkulus bill??)

    http://www.foxnews.com/politics/2011/04/14/obamas-5-billion-weatherizing-program-wastes-stimulus-funds-auditors/

    Greenies will promote it

  13. Myron Mesecke says:

    Even I have thought of a double decked roof with flow through ventilation design. Common sense for the Texas heat and we rarely get any snow or ice where I am.

  14. I have ridge vents on my house, which were billed as a way to allow passive airflow and let
    heat out of the top vent. Problem is, this only happens when the wind blows, which it never does during a typical Florida day. My attic gets to over 140 degrees, and since the morons ran the duct work thru the attic , the air in the ducts heats up while sitting for the next AC cycle and even during steady state conditions, gains 8+ degrees travelling from the source to the room vents. It is impossible to adequately cool this house. If the building codes had any intelligence, they would require interior ductwork – note that any airduct leakage in this case is irrelevant- the leakage is to interior space. Blown in insulation protects me from any transfer of heat from attic to my interior. Note that even if this newfangled roof manages to keep attic temps close to outside ambient temps, that would still have attic ductwork running thru 90 degree plus temperatures, rather than the 70 degree temps on the interior if located there. Moral of the story – put ductwork within the interior conditioned space, where it belongs. That would save far more energy than anything anyone can do with a roof.

  15. Scute says:

    I had a friend in Italy with a south facing study which became too hot in the afternoon. We made up a flat box unit, black-faced and attached it high on the south wall. Then used ducting to effectively connect the box to the cellar with the studio inline. The radiation on the box powered the passive system, drawing cool air from the cellar and through the studio. The cellar was air-leaky which was fortunate but so was the studio which was less fortunate. It worked, but the box needed to be roof-sized. A professional system, linked to a large cellar, underground carpark or purpose-built cut and fill concrete tunnel would take this idea further. The key is getting the driver (the sun-facing convector) the right area/volume for the volume of the building and cool reservoir. It needs to be matt black on the outside and insulated on the house side because, although part of a passive system, it is has to be seen as the driver of the system, required to do a lot more work than the system described above. I think the perfect application for this would be in a purpose-built supermarket with all sun-facing walls acting as convectors and where the cool reservoir is an underground parking/ delivery area. Air is drawn up to ground floor level, across the floor (not rising) and out at or very
    near the base of the walls. Then up the convectors. The supermarket entrance would be ten feet up with steps down so as to prevent cool air loss. The cool air would hopefully flow exactly where needed- where people are shopping i.e. 0-6 feet.

  16. MarkW says:

    A 20 year payback for a retro-fit? Thanks, but no thanks.

    I’d love to know how much this would add to the cost of a new roof.

  17. lurker, passing through laughing. says:

    Double layered ventilated roofs are becoming in creasingly common as a high cost custom option on homes in the Houston reas. I wonder how a three layered roof would hold up under strong windstorm stresses?
    I wonder how the very high cost of a three-layer system like the ORNL example pays off compared to a two layered solution or just a well ventilated radiant barrier more taditional roof?

  18. lurker, passing through laughing. says:

    sorry…. I think a good solar powered roof vent system might be a nice compromise.

  19. dp says:

    In Washington State wasps and spiders love these crown vents. They quit working when snow covers them but that is just for a few days each year. Same with low-profile stand-off roof vents. Humid air from inside the house is a problem if it gets into the attic space and freezes when the ventilation system quits working. Still – in a new construction it looks promising.

  20. kadaka (KD Knoebel) says:

    Paper: M$ Doc, 1.0Mb: http://info.ornl.gov/sites/publications/files/Pub30786.docx

    Warning: This was given as a link to the paper by Gizmag.
    PDF, 3.6Mb: http://www.nrca.net/rp/technical/symposium/pdf/17_miller.pdf
    It’s actually a stack of glossy handouts with pics and graphs, a press release kit. But it does have some usable info.

    From the paper:

    Winter Field Tests of the Prototype Roof and Attics

    During winter nights, field data revealed that night sky temperatures were much lower than the surface temperatures of the test roof systems, a situation that drives radiation heat loss to the sky. Good roof design should ideally limit heat gains during the summer while also limiting heat losses in the winter, which is why insulation works better than cool roof systems in cold climates. As shown in Figure 5, the ventilated and insulated roof assembly limits daytime heat gains from 8 a.m. to 6 p.m., which does not benefit a home during winter months. However, it also limits the nighttime losses as compared to the base assembly (Figure 5). The foil-faced OSB assembly limits losses occurring from 8 p.m. until 8 a.m. So the amount of heat retained at night by a ventilated and insulated roof deck must exceed the daytime penalty (Figure 5) for it to be adopted in cold climate design. Seasonal simulations are needed for verification.

    I’ve seen new home construction where attics aren’t even used for storage anymore, there’s a small access door, and electrical wiring is simply laid on top of the joists. Mere residents shouldn’t even be there.

    So why not go all the way, and make attics part of the heating system? The attic “floor” is done like a roof, completely sealed away from the rooms, fully insulated. The attic ventilation is closed off by switched vents, heat is allowed to build during the day. Then at night, vents are opened and the stored warmth is used for heating until it is depleted. That’s “winter mode”. To accommodate summer, vents to the exterior are switched open or closed to achieve no more than a maximum allowed temperature.

    I’ll also note that in this age of extreme caution, there’s the recommendation to turn water heater temperatures down to as low as 120°F to avoid kids getting scalded. A sealed attic under an uninsulated roof can achieve at least that with bright sunlight, and not just in summer. So stick an appropriate heat exchanger in the attic and use that heat for water heating.

    After that, might as well make the attic “floor” extra sturdy, and add some stone or gravel or similar thermal storage mass.

  21. Ray says:

    It might save energy but it won’t do anything good to the UHI (maybe greater night day differences).

  22. AJB says:

    Cold roof designs like this are fast disappearing in the UK, the days of permeable fibre insulation are numbered. Sealed warm roof designs using composite materials specifically designed for the job is the obvious way to go these days, even for refurbishment. e.g. http://www.celotex.co.uk

  23. Gerry Parker says:

    It’s actually as simple as adding a layer of foam (panel) insulation on top of the plywood and under (whatever) roofing material you choose, even without the air gap. I have chosen metal roofing due to the tropical nature of our weather and never had a roofing failure. It’s a shocking concept (apparently) to keep the heat out of the attic. Glad to see a proven idea getting some airplay, just realize it can be done more than one way.

    The foam panels can be had at retail for less than $1 per square foot, or like I did for may barn, you can grab them for free when a company replaces it’s roof. The biggest problem I found is that the screws for the metal roof are not common in the length required to screw through the foam panels to the decking.

    Gerry Parker

  24. All newer houses here in Perth have roof vents. Most are the size and shape of a pineapple and spin as they vent heat from the roof space. A design I assume keeps rain out.

    The thing is, I see them gaily spinning away in winter, when daytime temperatures average around 18C and nightime temperatures around 7C, and as people don’t have central heating here, houses get pretty cold. During the day, at least on sunny days, the roof space will be the warmest place in the house and these roof vents are cooling it down.

    A means to turn theses vents off in the winter would cost little and generate substantial energy savings.

    Its a pet peeve of mine that simple and obvious measures to reduce energy consumption like this are ignored, while billions are spent on boondogles like electric cars and carbon capture.

  25. Steve C says:

    Looks pretty good to me. Mind you, I say that as someone whose attic “room”, three floors up, has four airbricks facing into the prevailing sou’westerlies and neither heating nor insulation. Pretty much anything looks pretty good compared with that, although it’s almost usable for a couple of weeks twice a year, around the equinoxes. Century-plus-old building standards leave quite a lot to the imagination, like comfort … but hey, if you survived, you got to run the British Empire, which got you out of it and into someone else’s country! Happy days!

  26. Matthew W says:

    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.
    =======================================================
    From the looks of it, I would think for new construction, it would add little to the cost.

  27. michaeljmcfadden says:

    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

  28. Tom in Florida says:

    “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.

  29. Keith Minto says:

    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.

  30. Martin Clark says:

    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.

  31. jbutzi says:

    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.

  32. 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.

  33. J Cuttance says:

    can i get a plug for my roof idea?

  34. polistra says:

    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):

  35. koralis says:

    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.)

  36. Mike McMillan says:

    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.

  37. prjindigo says:

    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.

  38. george e smith says:

    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.

  39. 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 .

  40. Skeptik says:

    So the scientists have finally caught up with the tent fly.

  41. Keith Pearson, formerly bikermailman, Anonymous no longer says:

    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.
    ##############################

    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.

  42. rogerknights says:

    Curiousgeorge says:
    September 12, 2012 at 2:37 pm

    You can’t even get asphalt shingles replaced on a standard 1800 sqft house for under $5000.

    The article says it can be installed over an existing roof (4th paragraph).

  43. Les Johnson says:

    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.

  44. It’s suitable to aplied in tropical country like Indonesia

  45. Kelvin Vaughan says:

    So convection is used to cool the roof because radiation does not cool the roof.

  46. Bloke down the pub says:

    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.

  47. Petrossa says:

    My 300+ years old house has such a roof. Since when it was build. The more things change…..

  48. cba says:

    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.

  49. Randall_G says:

    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.

  50. SC_Conservative says:

    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.

  51. Jason says:

    Is this more efficient that a properly placed deciduous tree?

  52. GP Hanner says:

    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.

  53. SandyInLimousin says:

    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

  54. bob says:

    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.

  55. AC says:

    Pittzer @ 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.

  56. Myron Mesecke says:

    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.

  57. bob says:

    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.

  58. Frederick Michael says:

    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.

  59. pk says:

    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

  60. Mark Besse says:

    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.

  61. 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?

  62. Kelvin Vaughan says:

    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!

  63. Ken Harvey says:

    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.

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