Acclimation Is a Number, Not a Waiting Period
“The boxes were on site for 48 hours” is storage. Acclimation means the wood has reached the moisture content it will live at in that room — and the only way to know is to measure it.
The three questions to ask before a box is opened
- What moisture content are you targeting? There should be a number, and in Oregon it should differ depending on where the house is.
- What did the subfloor read? A solid floor wants the boards and the subfloor within about 2% of each other, or the floor will move relative to what it is nailed to.
- What is the house running at right now? A hygrometer costs about fifteen dollars and settles the argument.
An installer who has a meter and an answer to all three is telling you something useful about how the job will go. One who says the boxes have been on site since Tuesday is describing logistics.
The numbers
The National Wood Flooring Association specifies flooring at 6–9% moisture content, with the interior held between 30% and 50% relative humidity at 60–80°F. At 70°F and 40% relative humidity, the equilibrium moisture content of wood is 7.7% — comfortably in the middle.
In practice, western Oregon rooms sit toward the top of that band and Central Oregon rooms sit below the bottom of it. Winter interior humidity in Bend routinely runs 15–20%, so installers there work toward roughly 6%. That is not a regional preference; it is what the room will pull the board to whether anyone plans for it or not.
Why time alone does not do it
Wood in a sealed box does not exchange much moisture with anything. Wood stacked flat on a slab in an unheated garage acclimates to the garage. Wood delivered into a room that is not yet at living temperature and humidity — a remodel with the heat off, a new build still drying — acclimates to a condition that will not exist a month later.
The rule of thumb everyone quotes is three to five days. It is a rule of thumb, and it is the right answer only when the room is already at its living conditions and the delivered moisture content is already close. When either is untrue, three days changes nothing and two weeks may not be enough.
What it looks like when it was skipped
- Gaps that appear in the first winter and do not close in summer. The board was laid too wet and has been drying ever since. Seasonal gaps that open in January and close in July are normal and are not this.
- Boards pressed tight, with raised edges or a squeaking floor. The board was laid too dry and has taken on moisture with nowhere to go.
- A floor that moved in one room and not another. Usually a room over an unheated space, or one with a large south-facing window.
The expansion gap is the other half
Every wood floor needs a gap at every wall and every fixed obstruction, hidden by the baseboard or a shoe molding, so the whole field can move as one. Caulking that gap solid is the single most common way an otherwise good installation is ruined, and it is done with the best of intentions. The same applies to a floating floor pinned under a heavy kitchen island.
What this means if you are buying
If the quote does not mention moisture content, ask for it in writing. It is a fair question, it costs the installer nothing to answer, and in a state where the correct answer changes by a hundred miles it is the clearest signal you will get about whether the person quoting knows the market they are working in.