Practical insulation and air-sealing techniques needed for a (sort-of) enclosed crawl space
(If this should be posted elsewhere- feel free to move it, or tell me where to repost it.)
I have a fairly typical Chicago-style, narrow (like 22'), 2-story, balloon-framed house that was built in the 1880s or 1890s, and converted to a 2-flat later.
At some point (maybe in the 2-flat conversion?), the 2-story back porch was enclosed, and the new siding was continued down to grade level- by adding some framing between the wood columns (on piers) that support the porch.
I've seen this many times, and I understand why the people did it. They wanted extra space, and expanding onto an existing porch looked like the easiest and most economical way to get it. Then, (and this last part is a guess) they felt that continuing the new siding down to the ground would look more like original construction- and not merely an enclosed porch. Clearly this isn't a good starting point for well-insulated, airtight construction, but fuel was cheaper then, and people had lower expectations with regard to draftiness and cold floors.
Unfortunately, another construction project made the problem worse. One end of the porch contains bathrooms on both floors- so there is plumbing in this barely enclosed space. Over the years that I've owned it, I've added some pipe heater cables and pipe insulation in the crawlspace- but if the winter is unusually cold, the pipes will freeze.
I'm planning on several long-term improvements:
* A tighter, well-insulated roof will reduce warm air loss thru the roof and should reduce cold air infiltration down low. (The house needs a new roof, so this will happen relatively soon.)
* Tighter, better insulated walls (I'm not planning on replacing the old, yellow, aluminum siding anytime soon- but when I do, I'll definitely add exterior rigid foam insulation.)
* A new sealed combustion boiler (The first floor's boiler is due for replacement, and a model with sealed combustion will get its combustion air without contributing to air infiltration like the current one does.)
But... what about NOW? What can I do- economically- to make the best of a bad situation? How can I protect those pipes that were misguidedly installed in the crawl space?
The bottom of the crawl space is gravel, and it's continuous with the soil outside. Is the heat loss to the ground as bad as the heat loss thru the enclosure? Should I be planning to insulate the "floor" (ground) - in addition to the walls?
If there was a compelling argument and a good design, I'd consider re-doing the crawl space walls. I don't like that they just end in the dirt- but I don't want to shore up the porch and dig a foundation wall, either.
To combat air infiltration and heat loss, I'm thinking of:
a) plastic sheeting on the ground and walls; well-taped on the walls, but merely overlapped on the ground. If there's another broken pipe, the water has to go somewhere.
b) 2 layers (total thickness 2" - 3"?) of XPS with staggered seams on the walls and floor. On the walls it could be fastened to the existing framing with wood battens- or with those nails with the big plastic heads. On the floor... hmmm... rely on gravity? How do I connect the floor (ground) insulation to the wall insulation?
This is a crummy little problem that will likely require a fussy, pain-in-the-butt solution. You deserve an award just for reading it. :-)
If it will help, I can come up with sketches and/ or photos.
Posted Aug 30, 2014 4:28 PM ET
Edited Aug 31, 2014 5:22 AM ET
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