How to measure moisture in crawlspace

5 Replies

In a few of my rental properties, the crawlspaces have a lot of moisture and mold in them. I have a plan of attack to deal with the issue, but I'm looking for a specific tool that you all would recommend to measure moisture/humidity in the crawlspace? I'd like to carefully monitor the moisture to make sure that what I'm doing is actually helping. Thanks!

@Zac P. There are probably several good methods but I just use a regular, hand-held moisture meter to measure the moisture content of the floor joists.  In an unconditioned crawl space, you would want to see readings between 12-16% MC.  

Out of curiosity, what's your "...plan of attack"?  

@Zac P. you need a hygrometer.  You can find thermometers at home centers for about $20 that also have a hygrometer built in.  It will measure the relative humidity (RH) and track the high and low readings for a 24 hour period.

@Zac P. yes, @Matt Clark is right, a hygrometer will measure local RH, and you may also want a hard-probe wood moisture meter as mentioned by @Account Closed , these are pretty cheap on ebay

I am wondering if anyone knows the best method... I can imagine that RH would eventually (or quickly?) affect lumber moisture readings, and also that RH can vary tremendously over the course of a day. A buddy of mine had to get logging RH meters for his containers coming in from Asia, and the readings were all over the charts - you could see when they hit the open water (vs inland shipping channels), and the readings varied 30%-50% during a 24 hour cycle. These were more than $10 though. Best of luck!

Some good measuring advice here... and what worked on my fourplex was a really good vapor barrier (over a bare earth floor) with no gaps, even up against wall. Then plenty of ventilation. There are some equations and such for the amount you need. And, of course, a very good sump pump hard piped to the gutter (I like the Zoeller). I hate going down there.... but an occupational hazard... but at least it is dry and airy...Best of luck

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