Acclimating hardwoods is the process of matching the wood’s humidity and temperature to the ambient humidity and temperature of your home. Because wood expands and contracts with changes in temperature and moisture, it is important to “synchronize” the wood with the normal living conditions in your house to the greatest extent possible.
If you fail to properly acclimate hardwoods, they will likely be mismatched to the house, which could lead to two unfortunate consequences. If the wood is at a higher relative humidity than the house, it will likely contract shortly after installation. Even though you install the boards tightly against one another, gaps will develop in the floor–as much as 3/32 of an inch per 3.25″ board. With prefinished floors this is particularly troubling because you don’t have a puttying and sanding step to allow you to fill the gaps.
Perhaps even worse than the development of gaps happens when the house is at a much higher humidity than the floors. In this case, as the hardwoods take on moisture, they expand, potentially forcing the boards out against perimeter walls, or worse, buckling at the joints, cupping, and pulling fasteners out of the floor.
This article is part of our hardwood flooring installation instructions. Click that link for an index of all the articles in the series.
How Long to Acclimate Wood Floors
Unfortunately, there is no 100% correct answer for how long to acclimate floors. A good “rule of thumb” is 7-10 days for installation over wood subfloors. If you have a moisture-meter on hand, you can test the wood; it should be at 11% moisture content or less (the goal would be the average of normal moisture content year round) The subfloor should be equally dry. Do not install wood over a wet or damp subfloor.
Note: If you plan to install over concrete, we suggest using an engineered wood rather than a solid. The slab should be dry and additional subfloor prep is required. This scenario is beyond the scope of this series of articles, because issues such as moisture wicking through the slab must be considered. Many engineered woods do not require acclimation.
How to Acclimate Hardwood Flooring
Acclimation Location: Hardwoods should be acclimated in the same room/level where they will be installed. Don’t make the mistake of acclimating the hardwoods in a basement when they are to be installed on the first floor. Basements are moisture-prone since higher humidity air is heavier and sinks. Even though it may present a sizable inconvenience, you should acclimate the wood in the same area as the installation.
Don’t Stack Boxes: Some hardwoods (especially exotics like Brazilian Walnut) are very heavy. You need to spread the boxes out around the floor. Do not stack 1000 square feet of flooring in the center of a single room, or you run the risk of floor damage/collapse. Further, stacking boxes doesn’t support good acclimation. Instead, place all the boxes flat on the sub-floor.
Open Boxes for Best Results: If possible, opening the boxes exposes the hardwoods to more direct airflow, which supports the acclimation process.
Run the Air Conditioner / Heat Normally: Run the air conditioner or heat just like you usually do. Don’t attempt to dramatically modify the house or the woods. Your air conditioner should have been running for at least 5 days prior to bringing in the woods (in other words, if you just got back from a month long vacation where the A/C was off, wait a week before bringing the woods into the house, and then another 7-10 days for acclimation).
Don’t Allow Hardwoods to Get Wet: You should always keep the hardwoods stored in a well ventilated area and away from any condensate. For most homes, this isn’t a problem. Never let hardwoods sit outside through a rainstorm.
Don’t Acclimate Too Soon after Construction: Some compounds, like drywall compound for instance, will put moisture into the air as they dry. Wait until all compound has dried and the house has stabilized around normal occupancy conditions.
Best Season to Install Hardwood Flooring
In the heat and high humidity of mid-Summer, even a well-cooled house may be at a much higher humidity than normal. While Summer is a very convenient time for hardwood installation, it may be better to wait until milder months, like those in Spring and Fall, so that the normal living condition of the house is best matched to the floor and an “average” moisture content level is reached.
Conversely, Winter installations can be problematic if the humidity is extremely low in the house, leading the floors to significantly expand and create forces across the floor when the humidity peaks in the Summer.
Consequences of Not Properly Acclimating
Talk to folks at the flooring store and you’ll likely hear some real installation horror stories. Don’t skip proper acclimation. Read manufacturer’s instructions. You cannot rush the process, and if you do, you may end up with a sub-par installation.