Foam insulation in the roof
user-144738
| Posted in Energy, Heating & Insulation on
We are in the middle of a massive renovation. Down to studs. Our house has hipped roofs with dormers on the second floor. No attic. Our builder has suggested rather strongly that we use foam insulation in the roof. He and the advertisement for the insulation claims substantial reduction in heat and a/c costs and claims no need for sofit or ridge vents. Can this be true? I hope this is our last renovation. I don’t want to be surrounded by a mess of rot in 5 years. What should we do?
Replies
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=72433.1
This is a good way to go. Just make sure that you get a R value of the foam.
Search for info on unvented roofs. Plenty of info here and at http://www.buildingscience.com
We roofed without vents and used Corbond as well as Icynene throughout. Love it, roof looks great...
I personally like the system, just be sure you get documentation from the foam installer or GC that will allow you to use a warm (no airspace) roof in your jurisdiction.
The documentation is specific to the manufacturer, generic info will not work here.
If you can do this I think you will be very happy with the results.
Garett
Here are a couple of sites you might take a look at.
http://www.buildingscience.com
http://www.professionalroofing.net/past/mar02/feature2.asp
Also there is an article in the May 2005 edition of the Journal of Light Construction.
I tried to get the building department here(Ft. Worth, Texas) to approve this but they said that they had never heard of such a thing. I don't think they do very much outside reading. The 2003 IRC is the edition of the code that is used here and it says that all attic shall be vented. As I understand it, this is approved in the 2006 edition.
Hope this helps. Lot of luck.
Besure to use a closed cell type foam I use corbond no water vapor condensation.
Icyne allows vapor to pass through but I don't know if enough would condense to cause a problem.
"Icynene allows vapor to pass through but I don't know if enough would condense to cause a problem."
The lead article in last June's ( I believe) Energy Design Update newsletter featured a house where the Icynene was moisture soaked to the point that drops of water could be squeezed out of it!!! Yes, Icynene is very permeable. You have to control interior RH's so there will be very little diffusion into the foam or install a VB.
Where was the house?Icynene suggests an impermeable paint job as VB, only necessary in Madison WI latitude and above.Buildingscience says for Boston *don't* use VB to allow drying of melting snow to the interior (so they implicitly advise against closed cell). OTOH vapor retarder for Aspen.
This was a small house/large cabin (14' x 24') in Vermont.
In a space that small what created enough moisture to saturate the insulation?
Was it a bunk house? Commune? Did it have an un-vented gas heater?
Garett
(1) Vapour barrier should have been installed. Icynene recommends one over 7,500 DD; this locale had about 9,000 DD
(2) Indoor RH was much higher than normal; at times, 3 people living in this small house.
(3) Icynene reduced natural air change severely, compounding the high RH's.
(4) Only mechanical ventilation was bathroom fan controlled by the occupants.
A case of nobody understanding what they were creating from the design stage onward!!!!
As I've said in other posts:
re-train/learn; re-train/learn; re-train/learn; re-train/learn
Edited 4/29/2006 6:54 pm ET by experienced