Thread: Mold/mildew below OSB subflooring

I commonly find a small amount of mold/mildew growth below OSB subflooring in the crawlspace. Usually it's black, thin and speckled, and does not rub off easilly. I know that this is commoly found. Just wandering how others describe and report on this.

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First and foremost, this crawlspace needs a poly barrier. The first step in effectively conditioning a cold musty crawlspace is to properly apply 6 mil. sheets of polyethylene barrier throughout the entire floor area.

I always report to have any mold build-up professionally removed and treated.

It had a 6 mil vapor barrier on the crawlspace ground. That is standard around here. And it had plenty of open crawlspace vents.

I report it as microbial activity in the crawlspace due to high moisture levels. Recommend cleanup as per EPA guidelines, add vapor barrier and vent space as per local building codes.


//Rick

I see it on framing lumber routinely and don't report a thing.... I've heard it called "lumber fungus" - it grows on the wood while sitting in the yard before construction. Once dry, it's dormant and typically of no concern. I've talked to several mold specialists to arrive at my opinion.

Here's how I describe it.
A small amount of fungi growth was found on OSB subflooring in crawlspace. This is commonly found in newer construction. It's beyond the scope of the inspection to test for mold determine if this is a health hazard.

My feeling is that it's dormant. The crawlspace has no signs of excessive moisture, has vapor barrier and proper venting. My guess is that this occurs before or during the building process when materials get damp.

Matt, you are correct about the fungi growth and manufacturers. I too have seen this on OSB while it was still at the big box store. Another possible cause of the fungi is that some contractors have the OSB delivered to the job site and it is stacked on the ground for several weeks during construction where is subjected to rain, dew, and the elements.

If the crawlspace is properly vented and has a vapor barrier, I would note it (tell the good and the bad in your report) and that there is small fungi growth on the bottom of the subfloor.

Good morning, Gents -

A couple of comments: First of all, the presence of the mould on the OSB is common for a variety of reasons; not least of all because the mould may well have been on the OSB when it was installed.

Secondly, willy nilly recommendation of a vapor barrier can CAUSE mould to grow where otherwise there is no moisture issue. For example, in an house where mould has been installed on the OSB decking but there is no moisture problem and no mould problem and no vapor barrier - Installing a VB may result in a moisture problem developing and a resultant mould or WDO problem. A vapor barrier should only be recommended when it has been determined that that is the most appropriate corrective action. In turn that can only be determined by first determining IF there is a moisture problem (as already discussed, the presence of mould on the OSB is not necessarily an indication of a moisture problem). I have been involved in numerous "mould remediation" projects where we have corrected the moisture problem by removing a VB that installed for no apparently good reason.

Finally - I was involved in a very large "mould remediation" project where the builder spent thousands to remove the material from the OSB - problem was, it wasn't mould, it was ink. The idiot Certified Mold Inspector collected samples and guess what?.. they were "positive" for mould (no kidding). So before embarking on any corrective action, it is best to seek consultation from a legitimate expert - not a "certified" three day wonder who collects "samples or performs "tests."

Cheers!
CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Applications Consulting Technologies, Inc. - Home

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG