Looking for guidance on ventilation and insulation for attic to living space conversion
I purchased my first home in central PA earlier this year. One of the projects I’m planning for 2019 is to convert the attic space above the first floor into living space. Currently there are soffit vents on the north west and south east overhangs approximately every 4 rafter bays along with two ventilation fans.
For the portions of the roof sheathing that are currently insulated, it seems to be two 1″ thick sheets of foil backed polyiso insulation. These have been spaced out from the sheathing to create a ~2″ channel between the insulation and the sheathing. I have no way to verify, but I assume that the existing cathedral ceiling on the opposite end of the house is done in a similar manner, just without the attic fan. Other than knowing it was done ~10 years ago, I don’t know anything about the corrugated metal roof or what kind of underlayment was used when it was installed.
My dilemma is to what extent do I worry about ventilation when finishing the space given then there is no ridge vent, and even if there was one, it wouldn’t be effective for a significant portion of the roof?
A local contractor I used for an energy audit proposed the following:
– air seal all top plates and penetrations between first floor and attic
– add blocking above/bellow the existing knee walls then seal with closed cell spray foam
– fill joist bays of finished space with 3lb/cuft dense packed cellulose
– Apply high density cellulose to exterior wall and knee wall cavities.
– Add soffit vent chutes and fill unfinished attic areas with loose cellulose on top of existing fiberglass and cellulose.
In general the research I’ve done points to using dense pack cellulose in a cathedral ceiling like this is a bit controversial/risky, but has been used successfully in some areas. I’ve not seen much discussion on having only part of the roof ventilated as this contractor has proposed.
Any thoughts or recommendations the community can share?
EDIT: Was not able to upload any images to GBA. Please see the following link for images: https://photos.app.goo.gl/zq28mMkfPFCHeh9L8
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