Conflicting insulation advice from spray foam installers
I’m trying to determine the best solution for insulating our conditioned attic/unvented roof/cathedral ceiling and our walls. I have read so many articles/blogs/reports on GBA and from Building Science that my head is spinning. I know more about Joe Lstiburek then I care to, and I realize that fights can break out in blogs over who knows more about vapor drive. I’m probably staring my own theory war by posting this, but here goes. This will long, but I want to cover the details of the build upfront.
Climate Zone 4 Mixed, but very close to the line of Zone 5 – Owen County. We have very large seasonal swings in temperature and high humidity during parts of the year. It can reach 0 degrees F and on a few occasions even less during the winter. We have highs in the mid to upper 90s in the summer, and occasionally hitting 100 or more can happen
Current Build Status:
Framing done and dried in (windows/doors not yet sealed inside with canned spray foam)
Roof Stack-up (conditioned attic portion):
3/4″ OSB sheathing
Feltex synthetic underlayment
8:12 pitch standing seam metal roof – 0 penetrations through the roof i.e. no chimneys/vents/air stacks/etc
Roof Stack-up (cathedral ceiling portion):
same as above
2×6 wood stud wall
1″ XPS Foam
Tyvek Commercial D Wrap
DC-14 DrainMat by Green Guard (provides and R value of 1 according to manufacturer)
1/2″ Rough-sawn Plywood with 3/4″ Kiln dried Poplar spaced 1.5″ to 2″. (looks like reverse board and batton but uses less wood)
Jumbo tex and wire mesh over DC-14, then Coronado manufactured stone
8″ poured concrete walls on 3 sides (walk out)
14″ Floor Joist on top of basement walls
1″ xps foam from footer on the same plane as the wall 1″ XPS
An additional 1.5″ xps foam from top of concrete wall 4′ down (4×8 sheets turned sideways) to better insulate near the frost line
Walk-out Wall of basement
same as exterior 2×6 walls above
Now to my question, how to insulate from here on out? I feel I have addressed thermal bridging in the exterior walls but I have no exterior foam on the roof. I wanted 4.5″ of XPS, but the contractor could not be convinced to do that much rigid foam on an 8:12 pitch – he also felt the thermal bridging in the rafters would result in very little energy loss anyway. I held my ground on the walls, at least. He also suggested a cathedralized attic to make use of the otherwise wasted space in the portion of the home that would not have cathedral ceilings.
In order to do that, we planned to do spray foam directly under the roof deck. 1 of the 3 installers in my area refuses to use open cell foam, 1 will only use open cell, and the other says he recommends open, but will do closed cell if I sign a waiver for water damage due to a roof leak!!
Here is what I wanted to do:
4-5″ ccSPF under the roof deck
BIBS fiberglass (or installing batts myself) in the remainder of the rafters
1″ of foil faced poly foam attached to the bottom side of the rafters
T&G ceder for the ceiling in the cathedral section and dry wall in the bonus attic room section
NOTE: I realize I will not be able to insulate the 8″ trusses in the cathedralized attic as much until I add scabs on to match the 12″ rafters of the cathedral ceiling section.
Walls: BIBS fiberglass, Roxul, or Open Cell foam
Floor Joists: 3″ ccSPF followed by batts/roxul
So, how would you insulate this build? I’ve done so much researching and reading that my head is clogged with conflicting ideas. I think I would have preferred to NOT do spray foam if I had it to do over, but that is what the builder suggested before I began researching so much. With an unvented roof, it’s really about my only option at this point. Not that spray foam can’t be done right, it’s just that it seems to be a bit riskier and we still don’t know all the effects it MAY have down the road.