Planet Hardwood

To acclimate or not to acclimate?

The reason for wood to be in the environment of the occupied building prior to installation is to “acclimate” to the prevailing relative humidity (RH). Wood is hygroscopic, that is, it acts like a sponge, either soaking up moisture or giving up that moisture to a drier environment as it arrives to a balance with its surroundings. This balance, where the wood is theoretically inert, is called the “equilibrium moisture content” (EMC).

During construction, especially new construction, there are wild swings in RH. This is not a good environment for wood acclimatization. Even once the building is occupied there are seasonal swings in RH, especially in places like Vermont where we experience near tropical weather in the summer, to bone-dry conditions in the winter. Without any pro-activity towards limiting this natural range of RH, like humidifying in the winter and de- humidifying in the summer, an occupied building in Vermont will fall outside wood’s “comfort zone” (and people’s comfort zone) of 35% – 65% RH. So in Vermont as far as acclimatization is concerned, you’re always aiming for the bulls-eye of a moving target.

For wood to acclimate properly, it has to be exposed on four sides to an air current. This is accomplished by stacking the wood on “stickers” or spacers that leave gaps between the layers, with a fan to keep the airflow active. When wood is in a carton (as all prefinished wood is packaged) no real acclimatization is occurring, especially since either as a carton or as a pallet it is routinely wrapped in plastic. Universally, the first line of any prefinished flooring installation instructions, usually written in bold letters, is: Do not open the carton until you’re ready to install the floor. This caution is written because any wood not yet secured in place that is finished on the front, and not the back, has an opportunity for excessive movement in an extreme RH environment (like during construction). Once installation commences, it is advisable to work from a few open cartons to get a broader perspective on the material.

Everyone uses (or misuses) the word “acclimation” including manufacturers (!). We think it becomes a shorthand way of telling people not to leave the wood in the back of the pickup in the driveway during a rainstorm.

The saying “practice makes perfect” should be “perfect practice makes perfect”. So even if all the procedures were followed to properly acclimatize wood, one would want to acclimate it to the target average environment of the occupied building. During construction, the RH is usually not in the center of that target.

So introducing the wood to the site prior to installation is not necessarily harmful or beneficial depending on the jobsite RH.