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Community and Q&A

Follow-up to Spencer Burnfield’s question of 13 March: Closed vs. Vented Crawls in the Pacific Northwest.

user-1087436 | Posted in Green Building Techniques on

I’m still conflicted about closed crawls in the Zone 4 Marine climate of the PNW. Studies done by Washington State U. have shown that vented crawls “work” in this climate: i.e., they don’t cause the problems they cause elsewhere. Also, closed crawls allegedly exact a small energy penalty. Several local building experts have thumbed their noses at the East Coast “fad” for closed crawls. “The more vents the better,” one says.

To me, though, something doesn’t “work” just because it isn’t quite as bad as it is in other climates. I still don’t see the point of open crawlspaces. Why would you open this area right below your feet to outside air and insect infiltration just so you can stuff the floor joists with insulation that isn’t easily air-sealed? If closed crawls are so awful, then why do we allow closed basements to be built?

In our case, we’re building an 1800 s.f. house–on one story because my wife has Parkinson’s. 1800 s.f. is a lot more than the 500 s.f. or so of rigid foam that I would use on the walls and at the rim joist. As for the continuous air supply, I don’t see 5 min./hour (per J. Lstiburek) as a problem.

What do others think? I know Martin Holladay thinks crawlspaces are stupid, and of course he’s right. But that’s what they build around here. Anyone?

Last, forgive me. I must ask the toughest, most inscrutable question in Green Building. How does Joe Lstiburek pronounce his last name?

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  1. homedesign | | #1

    Gordon, Is a slab on grade completely out of the question?
    I agree with Martin that Crawl spaces are not-so-wonderful.
    I have also heard Joe Lstiburek say "the best crawlspace is NO Crawlspace"

    listen to the intro of this podcast for Joe Lstiburek's name....
    In Texas we say "Stee-Brick"

  2. davidmeiland | | #2

    Gordon, I'm sure you could easily build a nice closed crawl since you are building new. Make sure that the site profile and the foundation drainage are going to keep all rainwater moving away from the house, and that you downspout drains do the same. Grade the crawl floor nice and flat, put down a vapor barrier sheet that laps up the stemwalls, and pour a rat slab over it.

    Whether this will save energy, I don't know, that seems like it's still the subject of some debate.

    I dug some post holes at my place recently and hit water at about 2 feet. We have topsoil over a clay layer and the water is there most of the year, trying to evaporate into my crawl space.

    Building on a slab is also a great option, but you make future remodeling a lot harder.

  3. user-659915 | | #3

    Building on a slab is also a great option, but you make future remodeling a lot harder.

    Good point. You'll also miss out on a great mechanical space which if it's closed, not vented, will allow for a simple, efficient, easily configured and easily maintained plumbing and duct distribution space entirely within the conditioned enclosure, just where it should be.

  4. user-1087436 | | #4

    Reply to James Morgan: That too is a great point, and it's one I've been thinking about. I like having the guts of the house exposed for servicing, and within a conditioned space. That settles it, as far as I'm concerned.

  5. user-626934 | | #5


    My understanding of the history of vented crawlspaces in mixed-humid climates (such as most of the East coast), is that they worked well enough....until folks around here started insulating their floors AND cooling their houses in the summer. The combination of warm, very moist air in the crawlspace interacting with cool floor framing starts to cause problems in most houses immediately. The severity of the problems are linked to a) how moist is the crawlspace?, b) how cool is the house (and floor framing) and c) time.

    I suspect that vented crawlspaces "work" in the marine climates because you: a) have relatively little demand for cooling, and b) your typical vented crawlspaces have a much lower summertime moisture content than ours in the mixed-humid zones.

    Is there anything that says that sealed, insulated crawlspaces DON'T work in marine climates? I don't think so...they're just really short, insulated basements.

    Either way, though, vented or unvented...I still hate 'em.

  6. GBA Editor
    Martin Holladay | | #6

    All three options on the table -- a slab on grade, a vented crawl space, or an unvented crawl space -- can work in your climate, as long as everything is well detailed. The choice is yours.

    If you anticipate the need for wheelchair access, a slab on grade would be best. Crawl spaces perform best when the floor of the crawl space is higher than the exterior grade, and that puts the first floor so high that you need a long wheelchair ramp. I'd go with a slab on grade.

  7. auYWr29hu7 | | #7

    I wrote in on once before and you send me a picture of a crawl space with clear plastic installed to keep the moisture out. In parts of NJ we have a high water table most of the year it is fine but when the wet season is here if you don't pump your crawl space or basement out you have problems. In the new addition we had concrete put but some way we still get water so we have to pump them. The old part of the house has dirt. So when we first moved in I put heavy black plastic down but I didn't know it had to go up the walls. It cut down alot of the moisture but we keep a fan blowing the air around. I am fixing to put the plastic down like you had in the picture to try to stop the moisture from coming up most of the year. I will still have the pump handy for when it might have too much ground water. Do you think it is okay to put the clear platic on top of the black platic that is on the dirt?

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