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Need to vent uninsulated crawl space in the Pacific NW?

user-6900289 | Posted in General Questions on

I own an older house in Seattle which has both a basement and a crawl space. The crawl space has never had vents and has seemed to do fine thus far. However I just completed a basement remodel and the separation between the crawl and the basement is now more robust (insulated and reasonably well air sealed) than it was previously. I had planned to install vents after completing the remodel but after reading some responses on this site, I’m wondering if I really need to?

The fact that there haven’t been any apparent issues so far in the almost 90 year life of the house is encouraging. But I’ve changed the situation with the basement remodel.

Some additional information: the crawl space floor is covered with two layers of plastic sheeting. The crawl space joist bays have been insulated (fiberglass). Ducting and water pipes run through the crawl space. Both are insulated. No indication of standing water. Short term radon tests in both the basement and crawl space were both less than 2 pCi/L (although the crawl result was 1.9).

I had considered converting to an unvented and insulated (encapsulated) crawl space but after doing some research found that it didn’t seem to be clearly better than a vented crawl in this area and additionally may cause increased radon levels. Since I was already down the road on a vented crawl, decided to stick with that (and focus on other priorities!). But now thinking I just leave it as…

Appreciate any insight and advice you can provide!


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  1. GBA Editor
    Martin Holladay | | #1

    Assuming that there are no code issues here, there isn't anything wrong with "watchful waiting."

    The problem with this approach is that it's easy to forget about your crawl space, and not visit it for 5 years. If that happens, you may not notice the development of problems.

  2. user-6900289 | | #2

    Martin - yes, good point about forgetting about checking it... probably worth it to just do it the tried and true way and not worry about it. Thanks for the perspective!


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