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Our 2 1/2 story house dates back to 1912, which predates the use of insulation in these parts (Alberta, Canada).
I would like to insulate the top floor and attic, preferably putting the insulation on the underside of the roof so that the small attic space remains warm and I can use it for storage, something they didn’t provide much of in 1912.
So: any advice on how to proceed, vents, vapour barrier, unusual things I should watch for? The advice I am getting around here has typically not much contact with reality.
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What size are the rafters? Are there collar ties?
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The rafters are 2x4s, there are no collar ties, just a ridge board with 2x4s leaning up against it. Apparently this is the way they used to do it...
Simon
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I would attach rigid foam board (probably 1" Celotex) to the underside of the rafters and blow in cellulose above the foam. If you minimize air infiltration I wouldn't expect any need for ventalation. I would not want to use fiberglass without venting. If cellulose is not cost effective, go with thicker foam board.
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Help--I am re-roofing my 1954 Anchorage house only to find no insulation in most of the roof. (That explains the cold winters!) We have cathederal ceilings almost to the ridge line and have access to the 2x8 rafters only through the tounge and groove sheathing. We plan on using some sort of insulating material (blown in cellulite?) and then building a new roof over 2x2 stringers. Any suggestions?
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R.
I think cellulose dense-packed to 3.5 lbs/cf is ideal for this type of retrofit. Lift one course of the T & G and densepack the Cells, then replace the plank. If you get the cells up to the requisite 3-3.5 lbs/cu.ft it'll effectively air-seal the whole assembly. Isolate flammables such chimneys from the cells before blowing. Replace or get rid of any non-IC rated lights.
What is the ceiling construction? Drywall? T & G?
Why the 2x2's?
Steve
*HI Simon,You don't have a lot of room to work with there. I gather, given you haven't any insulation up there, at the present time, means you have not ridge or soffit venting either.Seems like most of the advise you've been getting wouldn't allow for adequate ventilation. The only way I can think of to give you some measure of insulation and still maintain adequate insulation would be to use SM styrofoam.This would require installing a 1x2 strip against the 2x4s all sides, up tight against the roof sheating. Cut the 1 1/2" thick SM to fit snug in between the rafters.Once that's done, install a second layer of 1 1/2" SM the opposite way or running the lenght of your attic. Install 2x2s in between to act as nailers later. This criss cross pattern will give you an effective 3" of SM insulation which will dramatically reduce your heating bills. With regards to the ventilation, you will be left with a cavity the lenght of your rafters. Make sure you have vent holes in the soffit area and follow up by installing a ridge vent that straddles the ridgeboard sufficiently to allow air to escape from both sides of the rafter cavities.Cover the inside with a layer of poly, and follow with drywall or whatever.Hopes this helps,Gabe
*Yuppers...Steve's got the ticket.
*Labor intensive lobster fest ideas if you ask me...but don't ask me as that's even better.
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If you are installing a well-insulated but unventilated roof in Anchorage you can expect heavy ice dam build up. With the heavy snowloads we get here the snow actually acts as additional insulation. Without some sort of ventilation between the insulation and heavy snow, the temperature of the roof deck will rise above freezing no matter what thickness or type of insulation you're using, melting the snow next to it. This water runs down to the eves, freezes and can build up to unbelievable thicknesses. The water backing up behind this dam will penetrate under shingles and into any available opening, causing water damage inside the home. If you decide to go with this "hot roof" design I'd suggest using waterproof membrane beneath the shingles (required by code) along the eves and valleys to at least prevent water penetration. The AK Craftsman Home Program is an excellent source of info for building up here. They suggest a minimum of 1 1/2" of continuous ventilation for cathedral ceilings. I assume that's what you had intended for the 2x2s?
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Our 2 1/2 story house dates back to 1912, which predates the use of insulation in these parts (Alberta, Canada).
I would like to insulate the top floor and attic, preferably putting the insulation on the underside of the roof so that the small attic space remains warm and I can use it for storage, something they didn't provide much of in 1912.
So: any advice on how to proceed, vents, vapour barrier, unusual things I should watch for? The advice I am getting around here has typically not much contact with reality.