I own a 24×26′ full dormered cape that was built in 1952 for $400. It was never finished and never kept up. It was built with rough full 2×4’s. When I bought it, it had to be completely gutted and rebuilt. The studs were furred out to be able to accommodate R-19 insulation in the walls.
My partner and I put in all of the proper vents and insulation ourselves. Unfortunately I found out recently we didn’t install the vents correctly and also didn’t add enough insulation. The rafters are only 2×6’s as are the ceiling joists. We’ve had some major problems with ice dams over the years since we bought the house. The attic space (such as it is) has 2 layers of R-15 in it – running in opposite directions. The dormers and steeper roof pitches have a R-19 insulation in them. The proper vents aren’t out to the roof edge and don’t fill the cavity between rafters enough. When we bought the house there was no soffit, so we had the contractor build one out. Unfortunately he only built it out about 4-6 inches, so it isn’t far enough out to maximize venting. So,after the insulation was installed we put in a 6mil vapor barrier, then strapping on the ceiling, then sheetrock. The dormer area has insulation, vapor barrier, 1inch foam insulation, then sheetrock. Most of our upstairs is unfinished, but we would like to put things in motion to get it finished.
Our contractor has said there are a couple of options as far as taking care of the situation. One would be to take everything back to the studs, reinstall the proper vents, install 2 inch rigid insulation, then add the strapping and sheetrock. Also insulation would be blown in to the small space left in the attic and the gable end vents would be sealed off. The second option would be to leave everything in place and add more insulation over it, then strap and sheetrock. We do have a ridge vent as well as the gable end vents at this point.
My feeling is that with 2×6’s, it doesn’t give us many options as far as insulating. It seems as though it would be a wise choice to get the proper vents installed correctly and maximize our venting. But, how do we maximize our insulation with a 2×6 once the proper vents are in place? A friend suggested using 4 inch rigid insulation between the rafters, which would create a 2 inch space behind. In this case proper vents might not be necessary.
I read the article “A Crash Course in Roof Venting”, but that would only work for us if we were doing new construction. We’re trying to work with existing conditions.
Any suggestions you might have would be greatly appreciated. I can send photos if that would help.
Thank you for your attention and sorry for the lengthy description.
Replies
haw
don't worry about the description being lengthy, usually little information is given-you have provided a good bit.
I would go to the Building Science website and look around. Your 2x6 framing is nothing new and I would bet, has been discussed in length there.
One important item you made no mention of-how well did you seal the various sources of warm air coming up through your existing frame? In many cases, you can track warm moist air from the basement that makes its way up, providing a good medium for ice forming at eaves/valley's and other less insulated or trapped areas (from venting).
Can lights, wire runs, plumbing vents, exhaust vents are good places to start looking and sealing.
insulating roof with 2x6 rafters
I'm afraid when we put this house back together (we had to gut the entire house when we bought it) 12 years ago, we had a builder who didn't do us any favors; a great guy, but his building practices have something to be desired. When will contractors be required to be licensed to build and remodel houses?
Anyway, I just looked down in the basement and indeed, none of our heating pipes, drain pipes, or the plumbing vent are sealed. Should I go around with some "great stuff" and start sealing up these areas? I'm assuming this is better to use than fiberglass? I just need to be careful on how much I fill the drilled or cut out holes. We do tend to get large bands of condensation on our windows when the weather turns colder. When the temperatures really dip those bands are often times ice. We put up a vapor barrier after the insulation went in. This goes for the upstairs as well. We have it on the ceiling, but I'm afraid I didn't seal up the overlaps with foil tape.
I'll check out the building science website.
Thank you for your help and information.
Even new capes are difficult to insulate and ventilate properly and to the extent that litlle heat will escape and melt the snow. Rather than rip things out inside, with no guarantee that it will be adequate, I'd concentrate on abating the ice dams on the roof. Either ice and water shield under the shingles, snow panels, wide exposed metal flashing, or metal roofing. A lot of folks just rake the snow off the roof eaves up about 3-4 feet, not easy on a full dormer but those often have rolled roofing which doesn't allow water backing up. Forget about heat tapes. You can see snow panels behind the turret.
even new capes are difficult
We do have ice and water shield, and rake about 1/2 of our roof every time it snows. Last year we got ice dams 1/2 way up the roof--not good. Some old timers around here suggest panty hose filled with ice melt and stretched along the edge of the roof. Other than unsightly (and we'd have to buy pantyhose) it would interfere with raking the roof.
As Calvin eluded to ... air sealing is as (if not more) important as ventilation of the attic to control ice dams. I've seen well insulated attics end up w/ 16" of ice on the roof ... due to high air leakage into the attic.
I insulated an attic once by simply applying 2-3" of rigid to the ceiling and sheetrock screwed through that into the rafters. Rigid insulation installed in restrictive areas (e.g. near the eave of the roof where attic space is a minimum) can help maintain R-value in a small space. I've also furred the rafters w/ e.g. 2x2 or even 2x4 to gain the depth I wanted.
Some would advocate a non ventilated approach I think ... Foam the rafters full.
Foam insulation and 1" airspace in a 2x6 will give you ~R-30.
Food for thought.
very helpful info
Thank you so much for this helpful information. What about strapping over the rigid insulation, then screwing into that? Would that help up the R-value? The house is only 24x26, so the dormer spaces aren't that large. If we go with foam, I'm assuming there wouldn't be any need for the 6mil vapor barrier?
Thanks again.
What about strapping over the rigid insulation, then screwing into that? ... 6 of one ... half dozen of the other, I think. The strapping has to be fastened much like the drywall, so not sure of the benefit (although there may very well be one that is hidden from our view ... yaknow? ... you do something and then realize why/how your method or shortcut doesn't work ... it's that hindsite being 20/20 thing). With e.g. Thermax applied and then strapping on top, you gain the bit of thermal insulation of the reflective surface and air space combo ... can't believe I'm actually supporting a 'radiant barrier' application, but if any one works, this is probably as good of application as can be had.
I'm obviously not intimately familiar w/ many details of your situation ... so at some point you'll have to take all of our food for thought and come to a personal decision about what's right for yourself.
Many/most foams have an inherent vapor retarder characteristic (i.e. perm less than 1.0), I think, so you're generally right about the 6 mil plastic ... but make sure when you decide what foam material to use ... to check the mfg recommendations/specs.