·6-8 mil black polyethylene sheeting overlapped 6 inches and taped
·Minimum 18” of space between bottom of joists and soil
·Extend a minimum 6” up stem wall
·Perimeter venting, 1.5 sq ft for every 100 sq. ft of crawl space
·Local building codes supersede
(Photo 6) Unfortunately, the 6-8 mil polyethylene sheeting is not the norm for building codes in many areas of the country and if it is installed; many times, it’s installed improperly. In areas of the country that have seasonal changes, many homeowners cover their perimeter vents to minimize those cold drafts coming up under the floors. What does that do to the moisture in the soil under the home without polyethylene sheeting? The moisture is trying to find balance/equilibrium, and will want to balance where heat and cold meet, at the subfloor where flooring is installed. If underneath the subfloor is not already enough to worry about now we have topical moisture from above that can affect the performance of the subfloor and flooring (Photo 7). Now the subfloor is getting it from both sides! Most manufactureres guidelines state no more than 12-14% moisture content in the subfloor. You will need either a pin type meter or non-invasive type of wood meter to determine moisture content (Photos 8-9). This number will vary depending on the type of flooring you are installing and the area of the country that you are installing. This is why flooring installers need to get educated about all aspects of subfloors. Because in the end, if the installer doesn’t do due diligence he or she is the one that ends up either having to pay for the replacement floor or getting a bad reputation, even though there may have been circumstances that were not the full responsibility of the installer. Just remember if you install over a deficient subfloor with flooring, and you accept the subfloor conditions as they are, you are stating you find the subfloor adequate for your installation so be prepared for the consequences that may follow. Let’s keep the money we earn, especially in these challenging times!