Replies

1. 
   andy_engel | May 21, 2006 09:30pm | #1

   You can probably get an engineer to sign off on an unvented roof to get it past the AHJ. Also, ask the panel manufacturer for help on this issue.

   Not all manufacturers require venting. I think that Elk doesn't. Check out some manufacturer's websites.

   Andy

   "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein

   "Get off your dead #### and on your dying feet." Mom

2. 
   Knightdiamond | May 21, 2006 09:31pm | #2

   Ya know, I don't have an answer but I had a discussion with an
   "Energy Efficiency" guy awhile back and his argument was, (and it made sense to me) A frame homes don't have vented roofs. Its just a "tilted" wall. (I am currently trying to build a cathedral ceiling with no vented ridge with a metal roof. Thats why we had this discussion) So whats the diff? Seems to me if you build it right it should not have to vent. (Under certain applications) Now, when I had another discussion with "my" structural engineer on the same subject he said it would get too hot. But I am here to tell ya that I have been in my attic when it was so hot you could not breath and I could not stay in there for more than a few minutes! Seems to me it was cooler out on the shingles! But what do I know. BTW- After I went to S. MS post Katrina to help a family member I was/am sold on metal roofs. The only one I saw damaged was one that had been hit by a piece of neighbors roof when it failed. All asphalt shingle roofs were damaged. Just some more than others. KD

1. 
   andy_engel | May 22, 2006 12:02am | #3

   FYI, venting's original purpose had nothing to do with controlling heat. It had everything to do with controlling moisture. Now, it's pretty common knowledge among building science guys that damp attics are almost invariably linked to damp foundations. The stack effect carrys warm air into the attic from the house. Where does the replacement air come in? Where the house's air pressure is lowest, the foundation. The air comes in, picks up moisture, and lofts to the attic, where in the winter, it condenses.

   Venting was written into codes in 1947 or thereabouts. Back then, the materials to effectively keep moisture out of basements didn't exist. They do now. Back then, they didn't understand air sealing the framing as a critical part of construction. A lot of guys still don't get that.

   Where the idea that venting would cool attics got attached, I don't know. I do know it doesn't work very well at that. And I also know that there are now far more effective ways to address venting's original purpose.Andy

   "Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein

   "Get off your dead #### and on your dying feet." Mom

3. 
   BobS | May 22, 2006 01:19am | #4

   In addition to Andy's suggestion of Elk shingles, Certainteed also allows unvented roofs in their warranty but they derate it somewhat.

   I'm not sure if there are SIPs like this, but there do exist foam panels with a vented osb top. Its a foam panel, then essentially some furring strips on top, then a layer of OSB. But there's no osb on the bottom, at least the ones I've seen.

   Check Altas Roofing's Crossvent panels.

   If you read some of Bill Rose's stuff you'll find the genesis of venting is suspect at best. I'm not sure that will help you with your building inspector. I'd think your SIPs installer should have some material to help.

4. 
   JonE | May 22, 2006 01:55am | #5

   There are a couple of manufacturers that do allow direct installation of asphalt fiberglass shingles on an unvented roof.  There are some special warranty conditions for doing so, I think.  I had the same dilemma and solved it by doing a cold roof system.  Mine was complete overkill, but I'm pretty much guaranteed that my roof won't leak and will last a long time.

   Basically, from the bottom up, SIPS, followed by a layer of Grace Tri-Flex 30 (because the roof was going to sit unfinished for six months).  When we finished the roof we left the Tri-Flex on there, installed 1x4 strapping, 1/2" plywood, a layer of 15# felt and shingles.  Ridge vent and eave vents and the roof is ventilated, yet we get the full insulation of the SIPS.

    

1. 
   experienced | May 22, 2006 10:22am | #6

   We have to educate the manufacturers and BI's to the recent and not so recent research!! In the past 1+1/2 years I have been able to get roofs on a couple of expensive homes ($500,000 & $1 million +)  through without venting.

   Armin Rudd of Building Science Corporation  in an Oct/2005 article titled "Field Performance of Unvented Cathedralized (UC) Attics in the USA" in the Journal of Building Physics reports that for dark gray or black south facing shingles (the worst case for heating due to colour and orientation) "on average, over the whole month of August, 2001, the UC attic shingles were 0.2 F deg warmer than the standard vented attic"    Notes: The UC attic is what we have been calling a conditioned attic. This was also in Jacksonville, Florida, where things get quite hot!!

   "Since the temperature of the roof shingles was not shown to be significantly affected by the presence of insulation, it was unlikely to affect the durability of the shingles."

   So what will the shingle manufacturers say now?? Bill Rose said if anything, having an unvented roof will give the manufacturer a way out of a warranty situation when the problem was the poor quality of their products. I have seen this with some light coloured roofs I have inspected in the past 2-3 years. These roofs used to last 22 to 26-27 years although only warranted for 10 years. Now I'm seeing their life reduced to about 15-16 years. One viewed last week had substantial granule loss - this was only 13 years old and I'm in the Great White North where shingles will never get as hot as Jacksonville, Florida.

   Seems we have one attic ventilation myth dispelled. Damn building scientists!!

   Edited 5/22/2006 10:59 am ET by experienced

   Edited 5/22/2006 8:59 pm ET by experienced