Advice for New Orleans Crawlspace?
Retrofitting my old shotgun in New Orleans. It sits on short piers above an open crawlspace. The floor is a single layer of old heart pink planks. There are countless airholes in it. Since it’s so humid here, I’d love to air seal it.
Every so often it will rain hard enough that there will be several inches of standing water, so encapsulating the foundation seems like a bad idea. So my one option would be to insulate the floor. I’m thinking of adding batt insulation between the joists and a layer of air-sealed rigid foam boards under the joists. I suppose I could use closed cell spray foam but I don’t want to put that on heart pine. And pulling up the planks to add a subfloor would be a hassle.
Assuming it makes sense to just insulate the floor, I have a few concerns. Termites are the big one. I worry I won’t be able to monitor them with this set up. And then assuming I actually get a good air seal, I worry that the floor boards will dry and shrink. My final concern is flooding. As far as I know this house has never flooded, but the possibility is always there. If water got into the cavity would I have to rip the air seal apart? I have this same concern for my walls.
My walls were formerly empty. They were just a layer of lathe and plaster on the interior and wood lapboard on the outside. I’ve added mineral wool to the inside, and zip to the outside. I haven’t air sealed them yet, and I doubt I’ll be able to make it very tight. If it ever flooded high enough for water the enter the walls would I have to rip away the lathe and plaster? I’d rather avoid that if I could. I would replace it with drywall, which seems less durable.
So I’d appreciate any thoughts on air sealing the floor, or how to react to flooding.
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Replies
I would use ccSPF if it were me.
I'm in a similar situation (pier+beam with water in humid environment) so I can tell you what I learned.
First, the water under the house is a huge problem whether you encapsulate or not. That's just asking for termites. You need to grade the soil around the perimeter away from the house. You might need French drain(s) and/or retaining wall(s). If the plan doesn't seem straightforward it might be worth it to hire an engineer for a consult.
Second, my conclusion is that the only proper way to insulate is to encapsulate. That's difficult in my situation because there's not a lot of headroom to work, so it would require a lot of excavation, but that's the only way. The house can't be raised because an addition on a slab was grafted onto it, and both the old+new parts of the house share common walls and a common roof.
My understanding is that the lack of floor insulation means that the warmth from the house is helping to dry out the joists, and that once you insulate the floor, you run the risk of mold and rot. That's why insulation should be on the perimeter walls with encapsulation, and running a dehumidifier with a drain to the outside.
As per this thread, sprayed closed-cell foam in the joist bays could be an option, but it's pricey, and if I'm gonna be spending a lot of money, I'd prefer to spend it on a better solution.
https://www.greenbuildingadvisor.com/question/what-type-of-insulation-should-i-install-under-the-floors-of-pier-foundation-house
Thanks for the feedback!
Drainage is tricky for me. Maybe once every two months there will be enough rain for the water to puddle for a couple hours. It mostly sits in the backyard but it sometimes gets into the crawlspace soil too. I may grade the soil away from the house at some point but my yard is relatively small so that won't do too much. The bigger issue is that the soil back there has a layer of clay under it. I've wondered if there might be a better drainage layer buried beneath that clay but I suspect it's heavy clay all the way down.
I've thought about encapsulating and including a sump pump down there. I worry about the pump failing though. I also don't understand how to manage the transition between the vapor barrier and the sump pump.
Sounds like you'd benefit from a consult with an engineer. I paid $250 for a site visit and verbal report about how to keep the crawl dry. Turns out I'd already had the right idea, away but he filled in some extra details, plus just getting confirmation from a pro was valuable.
Ok, what type of engineer would that be?
A "civil" engineer, though that's a broad term and covers all kinds of specialties, not just water diverting. Any kind of engineer that would do a foundation inspection can probably advise you. Here's the company with the engineer I hired, local to me, but I know not local to you, this is just to give you an idea of whom I found. There might not be a company that markets so specifically about rainwater in your area. https://www.watercache.com
I’m not sure why an enclosed crawl space is a better solution in a potential flood zone
freyr_design,
A couple of weeks ago a relative sent me their plans for review. Because they are in the floodplain of a nearby river, the designer set the framed floor on helical piles - but to maintain a nice relationship with grade, excavated under the house 18" deep, so that the bottom of the floor ends up several inches below the surrounding finished grade.
My head hurts.
Ha, perfect! Cheap pool
This article is good:
https://buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces