If there is one thing that comes back to haunt contractors, it is not knowing whether or not the wood is acclimated to their jobsite. The old idea of “leave it on-site for a week or two” still prevails among those not familiar with how and when wood acclimates. Standard [U.S.] milling will dry wood to a 6-9 percent moisture content range. That is usually good for most of the homes with a Relative Humidity (RH) between 30-50, and temperatures of 60-80˚ F according to the U.S. Forestry Department’s chart familiar to those that have attended NWFA classes (see below).
Warning though, no two jobsites are alike. You need to know the RH and temperature the owners plan to live in so you know where the wood needs to be for the most stable outcome of your project.
Use your moisture meter and test the wood (40 tests per 1,000 SF) upon receipt, delivery to jobsite, and continuously if the job lasts longer than a few days. Test your subfloor as well (20 tests per 1,000 SF). Test the RH and temperature. Mark your findings and determine where the sweet spot is. In future tests, note any unusual variations that can save you from inadvertent de-acclimation from other trades. It’s best to record and photograph your tests and save them in the client file. Should something happen down the road, you have the data an inspector needs. So many contractors are caught “deer in the headlights” when a failure gets inspected and cannot produce the data the inspector requests.
Acclimation is perfect if you are on target to the RH/temp numbers according to the U.S. Forestry chart. Consider that there are elements not in your control that may persuade you to install when the floor is not ready. Avoid falling into this trap at all times. It will not matter to the GC, the owner, or the judge if the floor failed when installed improperly acclimated. You are the expert. You will be at fault for knowing better but still installing. Besides, how hard will it be to recover financially, not to mention mending the damage to your reputation?
As far as moisture meters go, there is no valid excuse as to why you cannot afford the most accurate, expensive testing kits available. To not spend the money on your meter, but gamble time and again on a floor not failing is foolish at best. Beg, borrow, find a way to get the best meter into your hands.
Take into account your special circumstances. Here in South Florida, I deal with crawl space homes that need wood acclimated up to 13 percent MC while slab homes that are well insulated and sealed off need 8.5 percent MC. My good friend Jason Elquest has the opposite conditions in Scottsdale, Arizona – they are so dry his meters are lucky to read moisture in his acclimated wood.
Learn your area, learn your meter, and make sure you take care of this very important part of your work.
To learn more about the importance of acclimation and how it affects wood, check out the recently updated NWFA Moisture and Wood Technical Publication.
Best of Luck!