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i’ll be installing tongue and groove spruce boards on a vaulted ceiling of an existing home (far northern climate). the roof is scissor truss (no energy heel) with not much more room for additional insulation in the attic (no extra space at the walls). i hope to sandwich an insulating layer between the new ceiling boards and the existing drywall for r-value and vapor barrier.
any suggestion on the best options to add insulation interior? i believe the reflective bubble wrap stuff will be safe in this application, but it not any great r-value and is a bit spendy.
any issues with having the old drywall ceiling surface stuck between two vapor barriers?
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Dear Jim,
The only problem I can see is the minimal contribution of the bubble wrap. It is extremely expensive for the R's.
A layer of foil faced PIC foam board is good. More is better. If the existing insulation is only around R20, you'll want to look at over-blowing. Don't let the tight eaves condition keep you from doing something good through the other 90% of the attic.
And you're hip to air sealing right? And the cellar is dry?
Regards, Fred
*thanks fred,i think we're ok on the insulation in the attic (about r-35 to r-40 or so...looks like r19 batts over loose glass). just looking to add some easy r-value before the new ceiling finish goes up. i was concerned that any foam board products interior of sheetrock would not meet appropriate fire code. you're thinking this is acceptable?air sealing is pretty good for an upgrade project (verified by blower door tests) and crawl space is very dry. thanks again, jim
*Dear Jim,I hate when you guys set me up. You have a BD test and then ask about bubble wrap? You must be toying with me.Most places will accept boards over foam.Best, Fred
*thanks again fred,no set up intended.... just pondering the fire safety factor. jim
*R35 to R40, and you're adding insulation?I'd question the value of ading any, unless you're someplace awfully cold....
*southcentral alaska. we get our share of really cold stuff...it's a long winter. i guess my thinking was to take the opportunity to have a sort of monolithic thermal break across the vaulted ceiling surface (as long as cost was reasonable).
*Dear BH,You make a key point about the diminishing effects of added insulation. In theory we can take the insulation U-values and add them to get a theoretical performance. But that never happens in a real house.Jim makes the point that a monolithic layer of insulation has a dramatically disproportionate performance when compared to batts.But the most important effect of this type of measure is the radical reduction of air movement through the ceiling. This can not be measured in R-values, but it is very real. In my experience, it makes the difference between a good house and a total lemon.Regards, Fred
*Alaska - Does it get cold there ???Just kidding - I tend to think more midwestern. I don't think the added insulation sounds like a bad idea. Actually, I don't think energy heels on the trusses would've been a bad idea either if you're that far north. Are they pretty common up there?
*they are pretty standard design now. this house was built in the 70's. not a whole bunch of thought put toward energy design. there's plenty of places in the upper midwest that are as cold as here....just not as long. thanks for all the input guys. jim