What an education! Tuition 'free'! Make new friends!
Most of the time I lurk or post on the Kitchen forum, but now the big picture reasserts itself for our 100-year-old Colonial Revival house, wood frame stucco with a slate roof. We live in southern New England. Over the ten years since we moved in we have renovated four bathrooms and just finished the kitchen. Air infiltration aplenty, since the walls are not insulated -- except for the kitchen, which was insulated with fiberglass bats when the walls were open -- and there are three fireplaces. The slate roof was partially rebuilt, with Ice & Water Shield and new gutters when we moved in and does not leak yet, but does form large ice dams, because the vented attic has very old rockwool insulation on its floor. So that's the big picture. I thought "a cold roof would be nice" and began to investigate how to achieve that. Various insulation contractors make various suggestions depending on the vendors with whom they have established relationships. Only recently have I learned (through the Home Forum) that blowing insulation in where there might be active knob and tube wiring is a big no-no. So a nice foam man stops by today, and recommends spraying closed cell foam under the roof --?in effect making the unfinished crawl-space attic a partially-conditioned space? -- I read in some places that this might cause the roof deck to rot if water infiltrates under the slate roof and is trapped by the closed cell insulation. But the foam contractor says that foam insulation also might even extend the life of a slate room by keeping the roof cooler, plus averting the formation of ice dams.
My head spins. My own profession can be complicated, but the care and feeding of an antique house is REALLY complex! The bad news is: not much has been done to this house in the last 100 years after it was built to then-high construction standards. The good news is: not much has been done to this house in the last 100 years. No one blew urea foam into the walls. No one ripped off all the old plaster and put in Chinese sheetrock that outgassed toxins. The old windows are single-glazed, but they operate well and haven't rotted, and we learned with our kitchen renovation that old windows plus caulk and putty can be pretty tight. Nicer storms than the current aluminum triple-track are further down the road.
I'm at something of an impass with this insulation issue. It's a Rubiks cube. The next step must be to find out where there is active knob and tube wiring, because we can't insulate over that. I'll ask our roofing contractor, a slate roof maven, what he thinks about foam under the roof deck -- but my impression from you all is that this can be a serious mistake. In that case maybe I'll just huddle in the toasty kitchen in cold weather, put a wood-burning stove in one of the fireplaces, and wear a nightcap to bed, just as my ancestors did.
Mainly I want to say thank-you to those on Gardenweb who are so generous with their experience and insights.