I live in Louisville, Kentucky, so we have relatively cold winters (nighttime lows consistently below freezing) and relatively hot, humid summers (daytime highs consistently in the muggy 90s). My house was built in 1905 and seems to have originally had a cellar/crawlspace. During a renovation in the 1990s, they poured a concrete slab in the basement and concrete walls halfway up the existing brick foundation. But they only did that in the northwest corner. The rest of the basement is a crawlspace with about 2 feet of clearance between the dirt floor and the joists of the first floor. The created basement is where the water heater and furnace live, and duct work runs through the crawlspace.
The only separation between the crawlspace and the basement are some planks that are nailed into studs that run from the new concrete half-walls to the floor joists.
I would like to insulate the crawlspace and basement. Here's what I think I'm supposed to do:
Cover the dirt of the crawlspace with 6 mil (or thicker) plastic sheeting that runs up the foundation wall and attaches below the sill plate.
Attach 2-inch extruded polystyrene foam insulation to the walls over the plastic. Here's where I have questions.
- Should this insulation go from the dirt floor all the way up to the floor above, hugging the wall as I go up, or should I stop just below the top of the brick foundation so that the sill plate and joists are left visible for termite inspections?
- If I'm supposed to leave a gap for inspection, should I place foam over the area and attach it loosely (maybe with just tape, so it can be folded down during an inspection) so there's some insulation there, or is the fact that it's not securely attached mean it's not worth doing?
- It seems that I need a 15-minute fire barrier over the foam, and 1/2" drywall is standard. Do I really want to put drywall on top of plastic in my crawlspace? If it gets damp, that could be awful. Could I use cement board instead? Apparently 3 inches of mineral wool would also work, but that seems like an open invitation to dust. Apparently, you can just use an ignition barrier if the space isn't living area, but I would like to use the area for storage. Anybody have good ideas of what to use here?
What the heck do I do on the exterior basement walls? Should I run plastic down the outside of the wall so moisture can drain to the floor? (There is a sump pump.) Should I only insulate down a couple of feet below grade?
Any help would be greatly appreciated. I've been searching the internet for the past several weeks, and the more I search, the more contradictory information I get.