I’m done. Time for spray foam
We built an addition to our house which was finished in 2015. For the top floor we used attic trusses with a 12/12 pitch. We’ll phase 2 came along which was replacing the old 4/12 roof with a 12/12 pitch roof on the original part of the home and our structural engineer required us to sister two of the trusses in the addition where we made the connection.
它吸b / c我们不得不删除完成的墙。但glad we did, b/c we had mold on the underside of the roof deck. So, we just removed all of the horizontal drywall and confirmed it was everywhere on the north side. Noting on the south side. I attribute that to the sun.
the insulation scenario was as follows:
flat part of ceiling-r49 bat
sloped part of ceiling-4 1/2 poly iso leaving 1″ baffle
knee wall-r19 bat
The long and short of it was that the installer packed most of the baffles with bat insulation on either side of the poly so airflow was severely restricted. Fortunately, the mold is mild and will likely be remedied by over the counter products (we have a testing company come in next week).
So, I’m pretty much done here. The company that did the insulation has agreed to fix it inkind, but I am thinking I it will be better to just spray foam the whole dam thing eliminating the the soffits/ridge vents and the need to even insulate the knee walls (yes the floors are insulated from wall to wall).
The decking is OSB for this particular addition. I elected to use plywood on the 4/12 roof replacement but stuck with the OSB. The damage is minor by represents itself in almost every bay. My thought is that close cell spray foam will eliminate future moisture issues and I should be good from there. My questions are:
1. do they just fill the soffit holes with foam
2. do they just spray over the ridge vents
Anything else I need to be thinking about here?
Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hi David,
It's common to install blocking at the top plate to spray the foam against. And I think you should install something to spray the foam against at the ridge too. This way the foam won't expand out through the vent and onto your roof or glue the ridge vent assembly together making it more difficult to remove and close up when the roof is eventually replaced. I'm sure there are some GBA members who have done this before and will make some suggestions.
这里有一个很好的FHB文章阅读:Prepping for Spray Foam
And if you have any lingering questions about this roof assembly, I recommend this article:Insulating a Cathedral Ceiling
The usual thing the installers do is to stuff some mineral wool in at the soffits to give them something to spray the foam against. The mineral wool is better for this than fiberglass since mineral wool is stiffer. Once the spray foam is up, it’s the spray foam doing all the insulating work so the R value of the mineral wool that’s acting as a backer doesn’t really matter.
You’ll probably want to use closed cell spray foam in this application, BTW.
Bill