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Whispering Hill
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# Posted: 20 Jul 2023 02:54pm
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Our cabin, built in 2005, has a crawl space. Our foundation is pier and beam construction with plywood skirting.
The 4 ft. crawl space has a vapor barrier with crushed stone on top of it. Our maritime Canada island climate is humid in summer, pretty wet in winter.
We started out with no venting, then just a couple vents, left open spring, summer, fall, then closed for winter. We made the mistake of leaving some insulation down there which stored moisture, and developed a serious humidity problem in the closed space over winter. We ended up with wood fungus on several floor joists.
A few years ago I increased the number of vents in the space and left them open all year. While addressing the fungus back when it occurred, we still have moisture collecting on several of the joists and skirting.
I'm reading up on this and have noticed no clear consensus on leaving vents closed always, or open in the summer, then closed in winter.
This spring and summer have been unusually humid here and there still remains wetness on some wood. I have left the vents open, and am using a fan to try and dry things out.
I'm wondering how to proceed now. This house is shuttered for the winter, and since it's off-grid power is off, so no active de-humidification can take place.
Any comments appreciated.
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FishHog
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# Posted: 20 Jul 2023 04:38pm
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My opinion is lots of ventilation all year round
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Brettny
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# Posted: 20 Jul 2023 05:39pm
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I'm also building a new pier and beam foundation. We are doing no skirting and putting foamboard right up against the bottom of the subfloor. With no space I see no area to trap moisture in.
The problem with seasonal venting is it's one more thing to forget about. I'm trying to make a fairly maintenance free cabin. No spots for mice to live in, no gutters to clean and a metal roof.
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travellerw
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# Posted: 20 Jul 2023 06:50pm
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This is why I choose no skirting at all. I also couldn't find a consensus so I figured %100 open would pose the least amount of problems. Unfortunately, this means you must insulate the floor and if you didn't do it during the build, its a pretty daunting task (with lots of conflicting opinions also).
Once you have it fully dried out, you could research a good barrier paint (epoxy based). This would protect your wood and also stop any fungus issues if it does get moist under there.
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Brettny
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# Posted: 20 Jul 2023 09:37pm
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Quoting: travellerw Unfortunately, this means you must insulate the floor
If it's a weekend place you prety much need to do this anyway.
Whispering hill how did you "address the fungus"?
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spencerin
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# Posted: 20 Jul 2023 09:40pm
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Always vent it as much as possible. Yes, that *may* require insulating the bottom of the subfloor.
I put metal skirting up around my crawlspace and regret doing it, albiet not that much. I do like that it helps protect the foundation to some degree, makes exposed plumbing underneath less likely to freeze, and is more visually appealing. But, I, like you, get moisture on the joists and skirting near the perimeter of the building in the wintertime. My joists are treated and fasteners corrosion-resistant, so I'm not too concerned about this at the moment. Are yours?
I also cut some small vents in the the corners of the crawlspace skirting and hooked up a duct fan to help with ventilation. I also don't have a vapor barrier down yet - that's probably next year.
I guess that all is a little bit of extra work and expense, but I'd rather keep the skirting up and manage around it than to take it down.....
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spencerin
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# Posted: 20 Jul 2023 09:58pm - Edited by: spencerin
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Also, I think you won't find a clear consensus about it because it depends upon how well the crawlspace envelope is blocking out moisture to begin with.
Most crawls have dirt floors (even if it's a concrete block foundation), and even with vapor barriers down, it's still difficult to keep moisture out of the air space. So, ventilation is necessary in those cases (building code does set ventilation requirements for crawls).
But, some newer crawls have concrete floors, too, almost like a mini-basement. Those it's recommended to not vent and use a dehumidifier instead.
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travellerw
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# Posted: 20 Jul 2023 10:37pm
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Quoting: Brettny Whispering hill how did you "address the fungus"?
Only 2 things are used on boats. 1. Boric Acid 2. Borax. Both eliminate the current fungus and keep the new stuff from growing (for a while at least). It also acts as a weak insecticide which is a bonus. Mixed in water and either sprayed or wiped on (no rinsing).
I have heard people using dry ice blasting in "drug houses". Its supposed to eliminate the current fungus and if the problem (moisture) is removed, it won't grow back.
If I had growth on my cabin underside, I wouldn't hesitate to use Borax in water (however, unlike bleach it will not remove staining. It just kills the fungus/mold).
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Brettny
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# Posted: 21 Jul 2023 11:42am
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Never heard of useing borax. Bleach only works on the surface. White vinegar soaks into the wood and kills the cause.
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Whispering Hill
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# Posted: 21 Jul 2023 01:13pm
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Quoting: travellerw T his is why I choose no skirting at all. I also couldn't find a consensus so I figured %100 open would pose the least amount of problems. Unfortunately, this means you must insulate the floor and if you didn't do it during the build, its a pretty daunting task (with lots of conflicting opinions also). Once you have it fully dried out, you could research a good barrier paint (epoxy based). This would protect your wood and also stop any fungus issues if it does get moist under there.
I can see the motivation in lots of cases for no skirting. We have no insulation under the floor, and therein would be another absorbent material to hold moisture, depending on what was used. But this is also a seasonal residence (around June to November) so that sort of insulation wouldn't be necessary.
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Whispering Hill
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# Posted: 21 Jul 2023 01:20pm
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Quoting: Brettny Whispering hill how did you "address the fungus"?
It was a tedious job of scraping it off then spraying on a borate-based product. Luckily it was limited to a few boards in one area only.
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Whispering Hill
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# Posted: 21 Jul 2023 01:30pm
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Quoting: spencerin Always vent it as much as possible. Yes, that *may* require insulating the bottom of the subfloor. I put metal skirting up around my crawlspace and regret doing it, albiet not that much. I do like that it helps protect the foundation to some degree, makes exposed plumbing underneath less likely to freeze, and is more visually appealing. But, I, like you, get moisture on the joists and skirting near the perimeter of the building in the wintertime. My joists are treated and fasteners corrosion-resistant, so I'm not too concerned about this at the moment. Are yours? I also cut some small vents in the the corners of the crawlspace skirting and hooked up a duct fan to help with ventilation. I also don't have a vapor barrier down yet - that's probably next year. I guess that all is a little bit of extra work and expense, but I'd rather keep the skirting up and manage around it than to take it down.....
This house was a complete log home kit. Everything came in on a trailer. Now that I'm aware of the moisture impacts in the crawl space, I would have specified treated lumber for the joists. My builder, who installed the skirting, of course used treatment plywood. While it shows some dampness, there's no deterioration on it at all.
This really started the year of the sealed, unvented space WITH absorbent material sitting down there for months that the place was shut down. That got the ball rolling. This place can get some major precipitation year round and humidity is high -- much more than I've ever experienced here previously. There had been no problems in the past, vented or non-vented.
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Whispering Hill
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# Posted: 21 Jul 2023 01:53pm
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Quoting: spencerin Also, I think you won't find a clear consensus about it because it depends upon how well the crawlspace envelope is blocking out moisture to begin with. Most crawls have dirt floors (even if it's a concrete block foundation), and even with vapor barriers down, it's still difficult to keep moisture out of the air space. So, ventilation is necessary in those cases (building code does set ventilation requirements for crawls). But, some newer crawls have concrete floors, too, almost like a mini-basement. Those it's recommended to not vent and use a dehumidifier instead.
Yes, and even with our vapor barrier over dirt (which may not be that effective over 17 years?) it's going to get (and does get) humid down there. I just don't get a sense completely sealing the the space is the way to go.
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gcrank1
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# Posted: 21 Jul 2023 07:26pm
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40yrs on with our '83-'84 build, on silo blocks, one corner about 1' off grade and the others some bit more. No disturbed ground beneath (it was a sand & gravel hill in the woods at the family farm) and no vap-barrier put down. No skirting either; ie, free to breath.
NO issues ever.
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spencerin
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# Posted: 22 Jul 2023 10:24pm - Edited by: spencerin
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No, you don't want to seal it off. If you like the skirting and don't want to take it down, cut holes in it and add crawlspace vents.
What's your square footage? Code requires 1 sq. ft. net vent space for every 150 sq. ft.. If you have a good vapor barrier down, it's 1 sq. ft. for every 1,500 sq. ft.. And vents are supposed to be within 3 ft. of each corner.
Also, you can treat your untreated floor joists. You can buy the stuff and paint it on. That means crawling around down there on your backside painting for a while, but I have no idea how strong your DIY motivation is.....
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Whispering Hill
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# Posted: 24 Jul 2023 04:35pm
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Quoting: spencerin No, you don't want to seal it off. If you like the skirting and don't want to take it down, cut holes in it and add crawlspace vents. What's your square footage? Code requires 1 sq. ft. net vent space for every 150 sq. ft.. If you have a good vapor barrier down, it's 1 sq. ft. for every 1,500 sq. ft.. And vents are supposed to be within 3 ft. of each corner. Also, you can treat your untreated floor joists. You can buy the stuff and paint it on. That means crawling around down there on your backside p
Probably about 600 sq. ft. I think my vent ratio is pretty close to your specs.
Treating floor joists... Absolutely, and I'm looking at this product: Bora-Care with Mold-Care. Right now I'm running a fan and drying things up. Helps that weather conditions are less humid now.
My DIY motivation? I think I'd get an "A" in that department! I've been in that crawl space so much I should put a cot down there. 
Thanks for your input.
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Grizzlyman
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# Posted: 24 Jul 2023 06:30pm
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Maybe a dumb question- but why have the skirting? Why not open it up?
At a minimum I would think you could remove a few pieces to allow air to flow.
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Whispering Hill
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# Posted: 27 Jul 2023 10:23am
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Quoting: Grizzlyman Maybe a dumb question- but why have the skirting? Why not open it up? At a minimum I would think you could remove a few pieces to allow air to flow.
Not a dumb question at all. Probably not practical though for us, with some things stored there with no where else to put them, plumbing, water tank, supplies, etc. I'd rather not it all be left exposed. Our location is off the beaten track and I'd worry about some people monkeying around down there, especially as we board the place up for winter.
I've increased the venting and won't repeat my previous mistakes.
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ICC
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# Posted: 27 Jul 2023 02:57pm - Edited by: ICC
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Quoting: Grizzlyman Maybe a dumb question- but why have the skirting? Why not open it up?
Depends on the location. Here in the wildfire prone western mountains skirting can make a big difference whether or not the cabin survives a near encounter with a wildfire.
Windd can blow 'embers' as large as your fist a long ways. If those blow under an elevated structure that may be enough to ignite the floor or whatever wood is underneath.
A friend of mine has a cabin that basically has a non combustible exterior. Raised on piers it is fully skirted in roofing panels. There are plenty of vents and all are fitted with approved fiee and ember resistant screening. It survived a wildfire last spring while neighbors all around him bur t to the ground. S few years ago the fire marshall had recommended adding skirting for the very reason I first me tio ed.
My cabin is more or less the same but never subjected to a real world fire test.
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