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Acclimation of Hardwood Flooring in Northern Climates

Most hardwood and engineered hardwood flooring products need to be acclimated to their environment prior to being installed.

The problem in northern climates is that in the winter the air is typically, very dry and the relative humidity is very low. When hardwood is acclimated to its environment in the summer, it has been acclimated to an environment where the air is typically very humid and the relative humidity is very low.

Hardwood and associated products swell and shrink according to the relative humidity. In other words, if you acclimate the hardwood to a high relative humidity in the summer, the floor planks can shrink quite significantly in the winter unless the building’s HVAC can maintain the humidity moderately high.

The reverse is true. If the flooring was acclimated in the winter to dry air, the flooring can begin to swell and “cup” in the summer.

This year is very humid in many parts of the northern hemisphere. Flooring installers should be aware of this and take the necessary precautions to minimize potential expansion (cupping issues) and contraction (gapping issues). These measures done in the summertime can include but are not limited to:

-only acclimate the flooring to a climate controlled environment and in the same area the floor is to be installed

-install floors only after all wet work is done (drywalling, painting etc)

-never install hardwood below grade (unless the flooring was made for below grade installs)

- leave sufficient expansion gaps around the perimeter of the rooms and around any vertical abutments.

-ensure the settings to the air handling system are set to between 30-50% (preferably 40%) which may include keeping the dehumidifier on

-ensure that all substrates and subfloors are dry enough to receive the hardwood

-ensure that the moisture content of all the flooring planks are within 2% of each other

The installer should also make sure that all moisture readings are documented. The National Wood Flooring Association (NWFA) recommends measuring 40 boards for the

first 1000 square feet of flooring as well as four readings per 100 square feet thereafter. Similar measurements should be recorded for wood substrates.

If the flooring is installed over concrete then one of these testing methods should be used at minimum: Surface level testing methods

§ Plastic sheet test (ASTM D4263) – Non-destructive

§ Anhydrous Calcium Chloride (ASTM F1869) – Destructive

§ Moisture Content Meter (ASTM F2659) – Non-Destructive

o Sub-surface level testing methods

§ Relative Humidity Probe (ASTM F2170) - Destructive

We will discuss this more on our next blog post.

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