IMG_2910One of the most common indoor environmental  jobs we work with locally is the growth of mold in
a crawl spaces on the underside of the subflooring, floor joists, etc.. I have personally inspected a home that was occupied for 9 months and the moisture content of the OSB subfloor was still 70%. The sad part is this was leftover moisture from the original construction that never had the opportunity to dry out. I was brought into the picture after the occupants moved into this brand new house and became ill, not knowing originally it was from the mold growing under their feet. This problem doesn’t seem to be as much with older homes and wet crawl spaces, although it does happen in the older homes also. It is a problem seen more and more with new construction that had rainy weather prior to the roof being installed and/or sealed up. It seems that contractors are mislead by seeing a dry top surface of the subfloor and then continuing along with finishing the home, eventually placing flooring over the subfloor with no knowledge that it is still soaking wet just under that surface. With the home mentioned above the 3/4″ OSB subfloor was almost 1 1/2″ thick in some places when they tore it up, all due to the absorbing characteristic of the OSB product. I have known of contractors that have sworn off OSB in flooring, they are only using plywood as they had the issue in a new construction project and the price of remediation and the stigma of “mold” put on the house cost them a lot more than the difference in price between the two materials. Plywood is less susceptible to the issue, however it is not a cure if you let the water soak in, it can still grow mold, it’s just less likely to happen in the short time frame it takes for OSB to do so. The only advice we can give is to become educated in using moisture inspection equipment in your new construction or contract a water intrusion specialist to monitor your building materials if the rains come in contact with them during the construction process. Get the floor dry prior to laying any flooring and you should never have an issue develop.