News Worthy: Conditioned, Unvented Attics

Ed the Roofer

I just received this article from an Inspectors Website Forum and felt it was noteworthy for everyone to consider.

Ed



The concept of building attics as conditioned, unvented spaces has grown in acceptance in recent years, and this construction method has been advocated by the U.S. Department of Energy’s Building America program. A principal benefit of conditioned attics is that ductwork located in the attic is not exposed to extreme conditions.

With ducts inside the conditioned space, energy loss from leaks and heat conduction from the ducts is much less severe. The 2006 International Energy Conservation Code® specifies a default efficiency of 80% for forced-air systems, if ducts are located in an unconditioned attic. Where the distribution system is run entirely in conditioned space, such as a conditioned attic, the default distribution system efficiency increases to 88%, resulting in energy savings.

A new set of requirements allowing unvented, conditioned attic assemblies is contained in Section R806.4 of the 2006 International Residential Code® (IRC). The 2006 IRC requires that the surface under the roof deck, where moisture would condense, be maintained above 45°F on average during the coldest month. The 2007 Supplement of the IRC simplifies this by specifying the insulation levels that will maintain this temperature.

The IRC requires air-impermeable insulation to prevent moisture reaching the underside of the roof deck in all but climate zones 2Band 3B. If air-permeable insulation is used in the exempt zones, rigid board insulation may be needed above the structural roof sheathing to keep the underside of the roof deck above 45°F for the coldest month.

The IRC prohibits the use of a vapor retarder between the conditioned attic and the top-story ceiling of the house so that any moisture that does collect in the attic can escape into the house. A final requirement is that if wood shingles or shakes are used, they must be separated by a ¼-inch air space from the roofing felt over the structural sheathing.

For more information, see the Code Note, Conditioned Attics, at http://resourcecenter.pnl.gov/cocoon/morf/ResourceCenter/
article/1520.

For the full requirements of the 2007 Supplement for the IRC, See Section R806.4 of the code at www.iccsafe.org/cs/codes/2007-08cycle/2007Supplement/IRC07S.pdf

Source: U.S. Department of Energy’s Setting the Standard newsletter.

Chris Johnson

I've been pushing spray foam insulation on the underside of the decks for my clients for a few years now, my house is done that way as well.

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Teetorbilt

I know that my posts on the subject go back at least 2-3 yrs. At one point I was thinking about going into the spray-foam business but a survey of local homebuilders nixed the idea. Too expensive, they said.

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Ed the Roofer

Yes, it does seem to be the more efficient method and most energy prudent choice.

How would a contractor who does roofing specifically gear up to get more well informed in adding this as an add on business feature?

What gear and financial requirements would something like that entail?

What type of costs and profit margins are readily available? Is it as lucrative as I have seen mentioned by some inspectors who are more familiar with the product? Or, is the grass always greener on the other side of the fence?

Ed

nap

does the saving realized from the ducts being in a conditioned space (where they should be insulated anyway) offset the cost of conditioning the additional space? Effeciency is meaningless if the additional space that must be conditioned causes the bills to go up.

as well, you must maintain 45º+ temp on the underside of the roof deck? I must be misunderstanding what that is saying as it would require one to underinsulate to maintian that temp. That would seem to infer that a designed heat loss is required.

Chris Johnson

Teetor;

Spray foam here runs 2 - 2 1/2 times that of batts for same 'R' value, custom homes will spend it, hell they pay me for ICF's, what just build 1/2 a nice energy efficient home, start doing more and saving more.

Ed;

My buddy spent $ 80k for his set up, 26' enclosed trailer, big ass generator (I say big ass cause I can't remember the size, but it's big), spray equipment, air compressor, assorted tools, etc.

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Chris

neolitic

I intend to follow the links later,
but assume you already have, Ed.
Last ime I read up on this it was emphasized
that it was a whole house system.
Vent to exterior fans,heat exchangers...
Not just a matter of spray the deck,
and business as usual.

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Teetorbilt

Ed, I haven't done any more research since being shot down. Here are the resources that I aquired back then. All of the links were dead, here are the ones that I remembered (current links).

A basic sprayer was about $3.5K+. I've used these rigs for flotation on boats and they tend to be a mess to clean up, I hope that this has improved.

http://www.sprayfoamsystems.com/red.html
http://www51.honeywell.com/sm/chemicals/enovate/

nap,

http://www.buildingscience.com/bsc/
http://www.sprayfoam.com/cnt/docs/DeWitt_spray_foam.pdf

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Chris Johnson

The guns are still a pain to clean up from what I see

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Chris

neolitic

Ed--
You sure have been busy tonite!
Gonna take me a week to catch up
by the time I follow all the
links to links, on all of the threads
you began.

Thanks,

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Ed the Roofer

I got a whole chit load all in one e-mail from The Inspectors Journal Forum.

Good site, even though I do not frequent it much, but I have found a lot of very useful and informative links there.

If you or anybody else checks it out, I would recommend finding the library of archived documents and other such articles.

Ed

neolitic

I will, eventually....
I'm truly curious, cause last
time around the whole system
was not an inconsiderable investment.
Like I've said along way from
blow and go!

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tnt specialty

as is typical...they're 15+ yrs behind.....LOL....