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Karsten 12-13-2009 12:03 PM

Is it advisible to insulate under a ceiling

I stumbled across this site and almost found the answer to my problem in another thread.

This is my situation:

I want to insulate the ceiling of my mobile home (Vermont, double wide, built in 2000) more than what it is now. The roof structure are scissor trusses with blown-in cellulose above an airtight sheet rock ceiling. Shingles on the roof. The interior of the ceiling is sprayed with some sort of structured paint that results in air tightness or at least vapor barrier. According to the manufacturer the roof is insulated to R30, but I doubt it is that everywhere and I find it not enough these days. I will increase wall insulation and I want to add more to the ceiling as well.

The ceiling is high enough to add (maybe 2.5") to the inside but I do not know if this makes sense for a variety of reasons. I am worried about encapsulating the existing sheet rock in the ceiling. I also don't want to add too much weight but I plan to remove the shingles and add a metal roof to create more overhang one day. That should be lighter.

Does it make sense to think about rigid foam panels on the inside under the ceiling? If yes, should the furring strips be between the foam and the existing ceiling or between the new insulation and the new sheet rock? I am worried about moisture and condensation.

If it makes more sense to insulate on the outside, what do I do about the existing air space under the OSB panels? I could throw reclaimed 2" poly iso panels on top of the OSB after I stripped the shingles from the roof but what is the point if there is fresh air circulating underneath the new insulation? It would help with moisture but it would eliminate the insulation efficiency of the newly installed foam panels. Could/should I close the existing soffits and make sure that air circulates between the foam panels and the metal roof?

Any ideas/tips/advice? Pros, cons? Crazy?

Bondo 12-13-2009 01:31 PM


If it makes more sense to insulate on the outside,
Ayuh,... I would think the Best way to go would be Adding more blown in cellulose....

Karsten 12-13-2009 05:23 PM

"Ayuh,... I would think the Best way to go would be Adding more blown in cellulose.... "

That is a thought I have had but dismissed maybe too early. There is little room in those scissor trusses. I could maybe blow in a few more inches of cellulose but I would lose my attic ventilation. I hear mixed messages about whether this is acceptable for northern VT.

Is it OK to not have attic ventilation with a metal roof? I mean considering that the metal roof is screwed to strapping and that leaves a bit of space between the OSB and the metal? How about the shingle roof? Do I need to switch to metal right away or can I leave the shingles up a while longer even without attic air flow.


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