Best way to vent (or unvent) roof?
I am looking for suggestions on how to handle insulating this roof. The main problem is that where there are gables, there aren't any eaves for venting. The house is in Zone 6, I am looking to get R100 by insulating the rafter plane with dense pack cellulose. Am I better trying to build out a channel from an open eave to create venting or going unvented by fitting 5" of foam in the upper roof and finishing with cellulose. Neither idea seams great and spray foam would be very costly.
Pictures:
https://picasaweb.google.com/100264534486477190801/RoofVenting
Asked by Brian Van Handel
Posted Sun, 11/04/2012 - 19:11
Edited Mon, 11/05/2012 - 07:07
Posted Sun, 11/04/2012 - 19:11
Edited Mon, 11/05/2012 - 07:07
Yahoo
Technorati
Google
Facebook
Delicious
Digg
StumbleUpon
RedditOther Questions in Energy efficiency and durability
In General questions | Asked by Theresa Thompson | May 18, 13
In Energy efficiency and durability | Asked by Dan Kolbert | May 17, 13
In Green building techniques | Asked by Andy Chappell-Dick | May 18, 13
In Energy efficiency and durability | Asked by JOSEPH POLAND | Jan 15, 13
In General questions | Asked by Mike Goulet | May 15, 13
Brian,
Since it looks like your roof has at least one valley, it's not a good candidate for a vented roof.
It looks like a new house, which raises the question: isn't this a little late in the construction sequence to be designing the roof insulation?
Ideally, you would have included a thick layer of rigid foam above the roof sheathing before you installed the roofing. Is it too late for that?
Posted Mon, 11/05/2012 - 06:48
Martin, the house has a 12/12 pitch and is located on a steep hill. I had looked at guidelines from Fastenmaster and if memory serves me right, 5-6 inches of foam meant screws 6" on center. Not very buildable. Originally, I had planned on a tji roof and unvented roof throughout with 5-6" spray foam on the underside. The design was changed to trusses, which allow roughly 50% of the roof to be vented. Venting is by far a cheaper option as the trusses have enough depth for R100 of cellulose. I was looking for opinions on was to do with the rest of the roof that isn't easily vented.
Posted Tue, 11/06/2012 - 12:50
Brian,
Unvented roofs need either:
1. Rigid foam on top of the roof sheathing, or
2. Closed-cell spray foam on the underside of the roof sheating.
Another option, of course, is a SIP roof.
Posted Tue, 11/06/2012 - 14:15