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1941 house with brick veneer, no soffit, and fascia-roof deck gaps

cdruz | Posted in General Questions on

1941 Brick Veneer 1-1/2 Story Reno  with a couple questions/Issues.
Issue #1
I have a closed cell spray foam company that wants to coat the underside of my roof deck from ridge to top plate of wall. With the exception of the Living room which has had the ceiling vaulted and rafters doubled up from 2×6 to 2×12, all other rafters remain 2×6.
Initially I asked them to fill the whole rafter cavity depth-figuring that being in NW Ohio, I needed a minimum of R-30 to meet code and at 6.5R/in approximately that should suffice.
They stated that after about 3in of CC there’s no added benefit, but if the building inspector (as he did) says to fill the whole cavity they could do that. They then offered an alternative – to reduce the CC to 2in and fiberglass batt the remaining 4in – “flash and batt.” After hearing the alternative I was confused. Should I still request the full depth of the cavity filled? Or should I let them reduce it to 2in and batt the remainder? (If take the alternative, I’d rather have them spray and I’ll save some labor dollars and Rockwool/Roxul batt the remaining cavity myself.)

Issue #2
The house is brick veneer and Im turning the attic space into livable space. The Roof has No Soffits/overhangs. I’ll attach photos to explain visually. There is a gap of say 1/4-1/2inch between the roof deck and the gutter fascia around  the majority of the house. The living room I have vaulted is on the north side and when this area gets a strong North East wind accompanied by snow, the snow makes its way onto the top plate of the walls.
With reference to the vaulted spray foam insulating in Issue 1 – How do I seal this gap knowing there will be essential a “hot roof” design around the entire house and do so without trapping moisture in the air barrier between the brick veneer and black board sheathing?
Sorry its long winded, the more opinions the better, and I’ve seen one article on GBA that is close to Issue #2 but the person’s ceiling was insulated different and not vaulted… Thanks guys!

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  1. brendanalbano | | #1

    In general, flash-and-batt is a good way to use your spray foam in a cost effective way, you just have to make sure that the ratio of spray foam to batt is appropriate to protect your roof from moisture issues and to hit the R values you need.

    I'm assuming your part of Ohio is in IECC climate zone 5.

    If your local code says you only need R-30 (presumably on account of this being a renovation, or because a special exception for cathedral ceilings, as IRC requirements for your climate zone is R-49), and you have 5.5" in which to achieve it, 2" spray foam @ 6.5 R/inch + an R-15 batt only gets you to R-28, which may or may not be close enough to satisfy your building inspector (or yourself, depending on your goals for the envelope).

    You also want to make sure that 40% of your total R-value is in the spray-foam layer for your climate zone.

    In this case, R-13/R-28 = 46%, so you're okay as far as the ratio goes for the 2" ccSPF + 3.5" batt approach.

    All that said, R-30 isn't great for zone 5, and it might be worth considering how easy it would be to furr down your ceiling to get a little more depth to work with.

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