Hi all,
I did a search but there’s so much material. If anyone could suggest more specific search criteria for my situation I’d be very grateful.
Here’s the scoop though. I’ve a 1947 Cape Cod in central VA. There are no eaves at all so there is no ventilation into either the attic space or the rafter space. (As far as I can tell, there were never any gable vents either although many other houses of the same period around me have them). At some point in the past the attic has been turned into living space and most of it is now a cathedral ceiling. I’m going to have a bathroom put in, but I want to deal with any insulation/roof venting issues that there might be at the same time. According to Joe Lsiburek this is a Mixed-Humid climate and in his Builders Guide book (p.177) he shows a roof cross-section with eaves vents. I’ve searched the web for answers including more stuff from Joe L but the more I find the more confused I get. Anyway, I don’t have eaves vents so what would be the best construction? The underside of the rafters is 1/4″ panelling of some kind. That will be coming off and replaced with drywall.
Appreciate your help and Thanks!
Replies
I would use spray in place foam--remove the panelling from the underside of the rafters and have foam sprayed into the bays between, then drywall.
There are small vents available that mimic soffit venting. They are triangular, like chimney crickets, you simply mount them between the rafters at the bottom of the roof and vent the ridge .. not sure but think the one's I saw were made by maximum ..
I'm with Danno. Sprayed in foam eliminates the need for venting, provides much better insulation R-value per inch and eliminates air leaks in old walls/roofs.
Well, thanks everybody. It looks like foam then. What exactly is the foam called so I know what to say to bidders?
What treatment should the kneewalls get and the ceiling floor from the kneewall to the outside wall? The same?
Thanks again.
Use A urethene foam like Corbond.Another choice is Icythene, which has only about half the R-value and is not a vapor stop
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Thanks for your reply. Sorry I'm tardy in replying but my PC at home is kaput , I keep in touch from work and I've been away for over a week.
I didn't get any answers as to what should be the case at the kneewall and the ceiling from the kneewall to the outside wall. There is access to this area so would you foam that too or use batts?
Thanks again, David
Insulate the roof and leave the space behind the kneewall as conditioned space. The kneewall is just dressing to define a space in your case , as I understand your description. There are times when one might define the insulated space diferently and insulate from top plate in along cieling, then up the kneewall, then up the rafters. That method complicates things and creates more problems than it solves, IMO
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Hey Piffin..are you sure about that difference between Corbond and Icynene? I understood there is apparently a higher R value in the Corbond, but as far as I can see they are both otherwise actually doing all the same things. Can someone explain to me in simple terms the difference between the 'closed cell' and the 'open cell' spray in foams, and which is which.thanks
arthurhttp://www.thesmallbuildingcompany.com
yes, I am sure. Corbnond is a closed cell polyurethene which makes up a VB by its closed cell nature. Icy is an open celled structure that can get waterlogged.
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I'd go with the sprayed in foam too.
Guessing you have 2x6 or 2x8 rafters, there's not much room for insulation and if you try venting it even less.
Location might be helpful, there are BTers in VA, might be some help local to you.
Joe H
As Piffen said in Post #10, do all the way down the slope of the roof and the small triangular gable end walls to make the whole outer attic a conditioned storage space with access doors that do not need to be weatherstripped. This is the simplest way to do this space but many are stuck in the old method of doing the back of the kneewall and under the outer attic floor boards. See the end of:
http://www.eere.energy.gov/buildings/info/documents/pdfs/26447.pdf
Edited 8/2/2006 6:41 pm ET by experienced