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.
Thank you,
Ben
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Replies
Ben,
The correct approach is to remove the existing wood posts and to install a new foundation (CMUs or poured concrete) beginning at a poured concrete footing below the frost line.
You have informed us that you don't want to do that. So, now that we know that you don't want to fix this the right way, we'll talk about the wrong way.
Your method will work -- at least until the wood posts holding up the floors above start to rot.
Martin-
Thanks for getting back to me.
You've brought up a concern that hadn't occurred to me. Why would the wood posts rot? Are you saying my method would cause them to rot? -or are you saying that they're going to rot anyway? I think the post installation is normal/ typical; they each have their own concrete pier- like a deck foundation.
Thanks,
Ben
Ben,
Sorry, I misunderstood. I thought that these porches were supported on buried wooden posts. If the wood posts aren't in contact with the ground, they are in little danger of rotting.
A full CMU or concrete foundation is still the best approach if the crawl space includes plumbing. However, many people in your situation jury-rig walls between the posts, using pressure-treated lumber and pressure-treated plywood. It's not a great solution, because it's hard to keep out the wind, but people do it all the time. (These skirts resemble the skirts built in Vermont around the perimeter of trailers and mobile homes.)
My original post was way too long (as is this one)- and the reference to concrete piers was pretty well buried.
Undoubtedly, the best solution would be a real foundation wall, but for various reasons, I'm not ready to commit to that investment. Several homes in the area have been torn down and replaced with mansions; For the right offer, I might sell. Or, I could convert it back to a single family home, make some improvements (like moving the bathrooms off of the porch!!!), and sell it. Or, I could continue offering an economic rental option in a great town with great public schools. Wow. Did that sound defensive? :-)
I currently have the "jury-rigged" walls you described. I think they are adequate for the attachment of plastic and insulation that I described, but I'd consider building BETTER jury-rigged walls. Should I dig a shallow trench at the perimeter, construct skirts of PT wood that hang down into that trench, and then backfill with gravel? The intent here would be to keep critters out- while prolonging the life of the materials. Any better ideas? -concrete tile-backer board instead of PT plywood?
If the airtightness and insulation of the existing skirt are improved, won't I still have heat loss thru the gravel and under the skirt to the soil outside? If so, does it make more sense to try to insulate the gravel "floor" and connect that to the skirt? -or should the gold star, jury-rigged, insulated skirt extend farther into the ground- so the gravel under the crawl space is only in contact with deeper, warmer soil?
Thanks for your patience and assistance with this crummy little project.
Ben
Please let me know if some drawings would help.
For what it's worth, here's a link to some pics of corner/ end of the enclosed porch: http://www.delafleur.com/168_Elm/04_Rain_Barrel_02a.html
(Back of the house; the area with no stone foundation and the siding going all the way to the ground; note the ventilation fan and the absence of windows; this end of the porch has the bathrooms.)
Thanks,
Ben
Ben,
Q. "Should I dig a shallow trench at the perimeter, construct skirts of PT wood that hang down into that trench, and then backfill with gravel?"
A. Yes. Include one or two layers of rigid foam with taped seams in this assembly.
Q. "Any better ideas? -concrete tile-backer board instead of PT plywood?"
A. Either one would work.
Q. "If the airtightness and insulation of the existing skirt are improved, won't I still have heat loss thru the gravel and under the skirt to the soil outside?"
A. Yes.
Q. "If so, does it make more sense to try to insulate the gravel floor and connect that to the skirt?"
A. Yes, if you have the time and money to do the work.
Q. "Or should the gold star, jury-rigged, insulated skirt extend farther into the ground- so the gravel under the crawl space is only in contact with deeper, warmer soil?"
A. Either deeper vertical insulation or a layer of horizontal insulation on the crawl space floor would be better than shallow vertical insulation.