Insulation of timber suspended floor in basement
I have a ~100 year old timber framed house that was moved onto a concrete block walk-in basement in the 1950's or early 1960's. This basement was screeded in early 1980's (unknown if insulated or vapor barrier). The one wall that is above grade is ext insulated above grade only (about half), and this wall has a modern garage door. The other three walls of the basement do have their upper 1-3 feet above grade, mostly against crawlspaces lying under wings of the house. The house is on fairly sandy substrate on a hill, but nevertheless the basement regularly floods in springs (as Vermont snowmelt is pretty severe). Otherwise, the basement is fairly dry. It is an unconditioned space, used only for laundry, storage, etc.
Above this basement is the main living space. This is a 50-100 year old maple strip floor laid over ~6 inch softwood planks, open to the basement (fairly regular 3x8 joists, not entirely regular spacing). The house is reasonably insulated for it's age, still far from air tight but not bad.
My questions are: I would like to insulate under the floor of the house (basement ceiling). I am not up for the expense of digging out the basement walls to insulate them externally. Question 1) any opinions about the worthiness of insulating the internal surfaces of the basement walls? The basement has some damp (including the walls which have no barrier), so I would assume this is not worthwhile and might invite trouble.
Question 2) It would seem to make more sense to insulate the basement ceiling (floor of house). What are the worries about condensation and vapor build-up? What material(s) would be advisable? I intuit that I am getting a fair amount of air movement through the floor so would like to restrict this and add r-value, but am hesitant to create a vapor tight space for free of moisture problems. This is a beautiful old house and I don't want to create mold/rot conditions due to condensation around the insulation (moist air moving from house onto colder surface of insulation). I have considered adding a radiant floor heating system to this while it's open. Advice? Would a space between insulation and underside of floor be advisable? What materials? What difference would radiant system make? How to finish the underside of insulation (drywall, netting, etc.)? I would like to keep the project green but above all else r-value, reducing air movement and not endangering mold, etc. is the most important.
Posted Dec 14, 2011 2:58 PM ET
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