Advice on an old house’s insulation plan
I’ve been soaking up the knowledge here on GBA for the past few years in preparation for insulation my house. This week I finally made some calls, and today I got a quote back from a contractor. I wanted to get some insight before I pull the trigger on this project because I have a few concerns.
Some background: I’m in climate zone 4, in the mid-Atlantic. The house was built around 1900, balloon framed, stone foundation with an original slate roof. Siding is building paper->1×8 sheathing->cedar shingles-> vinyl siding on top of that. House has zero insulation except for some old worthless batts placed sporadically in the attic by a former owner. We got a score of 8,000+ on the blower door test for an 1,800 sqft house… Maybe I should go live outside instead- it’s a lot cheaper and just as warm.
After pouring over this site and others for far too long, I was certain that I wanted dense pack cellulose in the walls given its capability to handle fire, insects, and moisture. Further, my wife and I plan on finishing the attic eventually, so I wanted to move that area inside the building envelope now while we’re insulating the rest of the house to maximize the rebate program through our utility company.
That was my intention, but here’s what the contractor came back with:
1) Open cell sprayfoam straight on the roof deck (1x8ish skip sheathing, actual 2×6 rafters). Specs say ‘Random Fill’ to 8.5″ @ R-30
2) Open cell against the gables. 3 1/2″ to R-13
3) ‘Top plate’ install rigid foam ‘fan-foil’ and seal seams
4) Exterior walls get drilled and filled for fiberglass
-Needless to say, I’ve got some concerns. First, open cell foam directly against a slate roof sounds like a disaster. Where will the water go if (when) the roof leaks? How will slaters change out a busted slate that’s stuck to foam? I told them to spec me baffles that can drain to vented soffits but am waiting on a response.
-Next, does open cell foam need a vapor retarder or barrier in my climate zone? It gets quite cold here in the winter and I imagine all of the warm interior moisture finding its way to the cold roof deck would be a bad thing. They didn’t seem concerned when I brought that up, and I could be way off base here.
-Lastly, given that it’s balloon framing, I though cellulose would do a good job of reducing air movement in the giant chimneys that are my exterior walls, but they quoted fiberglass. To be fair, some of the plaster is in poor shape and the contractor was worried about blowing the walls out, so I get it. Will fiberglass do OK in place of cellulose? Anything I should worry about with that?
Sorry this got so long but there’s a lot of detail I want to get right. It’s a lot of cash for us and, more importantly, I don’t want to do damage to the house.
Any insight is appreciated!
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