Vaulted ceiling insulation question
I am building a 50 x 60 workshop with 16 ft ceilings in Vermont. We do get cold … two years ago while building an living in an RV onsite, we had a week with nights of -30 and daytime highs of -10. We have only had a couple of days in the 80’s this summer and only average 5 days in the 90’s (have had none this year).
Anyway, was planning to use standard flat bottom trusses but like the idea of an insulated attic area …. gable end on the 60 ft wall so lots of attic in the center area of the building.
I am thinking about going with sloping flat trusses with a 24″ cord.
With 20″ of blown in insulation (say Owens Atticat), I will have about R-60 with a 4″ air gap between the insulation and the roof.
My question is on the vapor barrier.
We just built the house and a local energy consultant (a friend so the advice was free), had me leave out the poly! He had me caulk every piece of dry wall in place. He said the drywall would work as a vapor retarder (controller) and there would be less chance of mold.
We had poly up in one room (on an outside wall) … when we took it down, it was soaked and mold had started so I am guessing he was correct.
So, I am now trying to figure out what to do on this ceiling.
I can put no poly and caulk every sheet ( not sure what I am using yet … something cheap like hardboard).
I can go with the poly.
I can put house wrap between the trusses and interior wall sheeting.
Any thoughts on this?
Also, I want to maintain the 4″ of air gap as I blow in the insulation. I am thinking of putting the wrap over the rafters (between the top of the rafters and the roof sheathing) but then run it down 4″ (well 3 1/2 to the bottom of the 2 x 4 top of truss) then over to the next truss. I was thinking I may need say a 1 x 2 to hold it in place and tight against the truss.
The other idea is to use the preformed rafter vents. I found them for $1 each online ($2 – $2.50 local). Just a bit worried they look very flimsy. Also only an inch or two of gap.
Either way … about $500 to maintain the air gap.
Again any thoughts?
If I use house wrap on top to hold the air gap and on the bottom (between the trusses and internal sheathing) is this ok? Will cause any problems using two layers, one on top and one on the bottom of the insulation (again, thinking two layers that will stop moisture but breath, no poly)?
One thing that always comes into play is cost. This is a workshop and I am on a very tight budget. To save money, the walls are T111 nailed to the studs (wrap between) … no sheathing. Things line spray foam are out of the question. I did put sheets of foam under the floor, around the perimeter of the pad and out 36″ (poured the workshop pad when we built the house so just put the cost into the 30 year mortgage of the house). I can’t afford to put it on the inside of the building.
Thanks so much …
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