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Insulation for new construction

This summer I'm planning on building a new home in Greenville Maine.
No need to mention it gets cold in winter.
I plan to build using 2 X 6 studs and OSB exterior sheathing with housewrap followed by log siding.
I originally had planned to have expanding foam insulation throughout, but my builder says this is going to be expensive, the 5 1/2" depth of the stud walls. He suggested getting rigid foam insulation boards (Dow TUFF-R) to fill the first two inches, R-12, and then fill the remaining 3 1/2 inches with the expanding foam insulation for an R of about 34 and a thermal barrier over the interior studs before tongue and groove planking.
If I go with this method should I place the TUFF-R against the exterior sheathing or leave, say, 1/2" of airspace?
Also, the cathedral ceiling would be done similarly, with maybe 2 or 3 layers of TUFF-R followed by a 1" thermal barrier before the planking. Would I need a vapor barrier?
Heating would be by propane for underfloor radiant heat with a wood stove backup.
Thank you all for your valuable info.

Timothy Miller
Re: Insulation for new construction

Howdy, consider using 2by8"plates and stagger 2by6" studs 24"os and weave R19 or more fiberglass between the studs. This reduces greatly the thermo bridging of the studs . Case study in Canada found this raised the r value to what the insullation was rated instead of the actual r value of actual whole wall which was a dismal R3 in conventional 2 by 6 studs walls with R19 insullation. Just that simple hardly any additional cost makes an amazing improvement. I'd spray foam to control air infiltration at the bottom plate to foundation and electrical boxes etc. What flooring isullation are you considering? Consider R22. Also consider enginered trusses to allow more insullation at the ceiling to wall plate- otherwise this is a cold spot due to not enough clearance in the framing for insullation to match the rest of the attic. Also a 6 mill vapor barrior extended 1' out onto the floor and ceiling caulked to the wall plates warmside of the walls. Finally Using T vac air barrior on the exterior instead of the foam to save $$ over using the foam panels.

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