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Thoughts on 90% RH in a crawlspace? San Francisco Zone 3 Marine.

severaltypesofnerd | Posted in GBA Pro Help on
I’m working with a building that regularly clocks over 90% RH in the crawlspace, in an area where typical crawl RH is in the 60% range.
The last significant rains were over six months ago
This is near San Francisco Zone 3 Marine.
We just added a 6mill poly vapor barrier which dropped RH from mid 90% to mid 80%, considerably less than hoped.  That vapor barrier was dry laid but not sealed to the walls (yet).

There are four 1300 square foot crawls, each about 3′ high, plus an additional 800 square foot crawl.  Each crawl has a flat dirt floor at grade and a cripple wall with vents.  Above is a two story wood frame construction with stucco walls.  Interior units above have multiple mold problems, including mold regularly covering all surfaces of all walls (the tenants have been blamed — and in fact if they’re careful to keep things away from the walls it can be ok). 
The cripple wall wood is soft and punky, gone in places.
The dew point temperature is super close to the nightly low.
Any thoughts on what to test next?

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  1. andy_ | | #1

    What's the ground moisture like around the building and in the crawl? Do you think you might have water entering around the wall?

  2. user-5946022 | | #2

    1. Tape/seal the vapor barrier to the perimeter of the crawl and tape/seal each sheet to the next.
    2. Eliminate ground water getting into the crawl

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