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Heidi Kellner 08-30-2012 08:26 AM

Insullating Large Cathedral Attic in Old Victorian Home
We're still unsure about how to finish off the attic in our large old home. It has 1800 sq. feet of gables/ceiling and 700 sq. feet of gable walls.

Most insullators that have seen the space want to spray CCF but I have apprehensions about this process. First, the roof is 8 years old and was cheaper shingles layed flat on the tarpaper with no plywood down first, so the CCF would come in direct contact with the roofing (we're in zone 4/5). The rafters are old lumber with only 3 1/2 max. space to fill with the foam (not enough R value probably?). It's a very tall victorian and if there was a roof leak we wouldn't know about it and it's prohibitively expensive to find a roofer to get up there to deal with the roof. Plus it sounds like when you use CCF that you then need to condition the space 24/7, which means we can't close the space off when not in use, but still have to pay for some form of AC/Heating to keep the temp/humidity in good range. (One specialist said we don't need any air venting that you seal the space, the end, and another said we had to have an air venting system and his cost for that was an extra $1,000).

Currently we have 2 gable vents and 4 roof vents and soffit vents around, but the roof vents are only on two surfaces of the roof and there are more like 6 or 8 surfaces because of gables on every side. No ridge vents.

What I'm thinking would be a safer method than CCF would be to fir out my rafters another 2", leave some air space and cut insullation board to fit inbetween the rafters, install ridge vents and finish with one more layer of board and then drywall, probably having to sacrifice the peaks and do a slightly dropped ceiling - so the soffits would supply air up to the ridge vents, toe walls all around insulated on the backside as well.

Is there anything wrong with using the board and doing it this way?
Insights welcome!

GBrackins 08-30-2012 09:05 AM

a few photos would be nice

and if I understand your post correctly you are saying they laid tar paper over the rafters without any roof sheathing???????????

joecaption 08-30-2012 09:10 AM

No matter what type roofing you have there's no way to install it without something to attach it to.
There's no form or roofing I've ever heard of that's just layed over tar paper without some form of sheathing.

Heidi Kellner 08-30-2012 09:15 AM

no solid decking
there is no solid decking. you can see the black underlayment. the only decking is the old boards laid across the rafters which are many inches appart, so lots of roofing nails poke through the roof all over the place - make sense?

Heidi Kellner 08-30-2012 09:16 AM

there is spaced sheathing - no solid plywood deck - very odd to me and mentioned as odd by one other roofer who has been in the attic and not mentioned as odd by another

GBrackins 08-30-2012 10:47 AM

yes, that makes sense, especially if you have an older home.

plywood was not developed until the 40's, I believe after WWII so board sheathing was common. My old place was built in the 1850's and had board sheathing about 24" in width and had gaps between the boards so it could expand when it got wet. tar paper and weather resistant barriers were not required way back when, of course in most places there were no building codes either

Windows on Wash 08-31-2012 10:04 AM

Your idea of rigid foam with a vent space between the deck and the foam is a solid one.

You can either continue to add rigid foam to that space and cover the rafters with it until you get the proper R-Value for that region or spray with with foam as well.

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