Blown-in floor joists… cellulose vs FG… your opinion?
David Meiland| Posted inGeneral Questionson
I’m about to have an insulator install blown-in insulation in a 2×8 framed floor. This is Zone 4 marine, over a crawl space that is very well vented. He is willing to do either cellulose or fiberglass. What if any are the considerations?
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David,
You should read this
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces?topic=doctypes/insights
Torsten, thanks for the link, and let me offer an opinion that vented crawlspaces with insulated floor joists appear to "work" in this area. I go into a lot of them to inspect and work, and it is very rare that I find any sign of moisture problems. I've been in a wide range of them--some are short, some are tall, some are over-vented, some are barely vented, some have ducts and some don't, some have ground cover and some don't. Most of them have batts installed, and thicknesses vary. My guess is that these crawls are kept somewhat warm by the heated space above, the exterior air is not all that humid, and there's a lot of wind here to blow through most crawls and attics.
I have not paid close attention to the debate over conditioned crawls, but it's hard for me to imagine there's not an energy cost associated with them. If I were starting from scratch with a crawl space, I would probably pour a rat slab over foam insulation, then insulate the crawl space wall. In this case it would be really difficult (think: sawzall) to get rigid in there to insulate the ground.