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Acclimatization of Hardwood Flooring III
Why I say you acclimatize to the average of your homes relative humidity.

So first remember that acclimatization of hardwood flooring is the process of letting your hardwood come to equilibrium with the moisture content in the room or home of installation. Read Part I (should you acclimatize in the first place) and Part II ( how would you do it if you could?) of this dialogue if you haven't already.

So I promised to tell you why hardwood flooring installation should ONLY begin when the moisture content of the wood is equal to your average moisture content of your home year round.... "average" being the important word.

By average I mean if you have dry winter weather and the relative humidity in your home in January is 35% then this is your low end of the relative humidity (RH) scale.

At the opposite end of the spectrum is the hot and humid weather in August, at least in my part of the world. Temperatures can get up to as high as 90°. But remember we are NOT really talking about temperature (hot or cold) but rather the humidity index.

In Northern Ontario the humidity in August can stay in the 65% range, so the question to ask is; " What is the relative humidity in your home?." If you have air conditioning it is going to be significantly lower then outside. Lets suggest that it is 55% indoors.

That would make your highs equal to 55%RH and your lows equal to 35%RH. Note I've try to keep the math simple. This leaves us with a yearly average of 45%.

So why do we want to equalize our hardwood flooring to this average relative humidity of 45%?

I'll try to explain that by telling you what happens if you don't do this, and hopefully it will make sense.

Winter Dryness:
Lets say you are installing hardwood flooring in January and the air humidity is 30%. You do what you are told and spread out all this flooring across your living room and wait. Optimistically it all dries to 30% and you install it.

Now its August. The humidity has risen to 60%. Remember you installed all this flooring after it had shrunk to 30%.. its smallest size of the year. Now its 60% and the wood wants to expand. Where does it expand to? The only thing it CAN do is spread outwards where hopefully you have left enough expansion space that it won't get jacked against any walls or other flooring.

This puts a lot of stress on your nails and tends to loosen their connection with the subfloor.

Summer Humidity:
Here's the opposite. You have laid out all the hardwood flooring across the same floor but now the humidity is at the upper extreme. The wood swells to its largest size. Now what happens?

You install the flooring in this expanded state. We hit January. Winter dryness strikes again and you get gaps! The floor boards have shrunk to their smallest size. You get on the phone and start yelling at me that either my product is defective or the installation was incompetent. But nature has taken over and wood has reacted as wood will! Relative humidity goes down and wood shrinks!

So Why Average?
It might now be obvious. If you install your flooring at its average moisture level then through the process of seasonal expansion and contraction the wood and the nails that are holding it in place only move half the distance.

In summer they expand from 45% average to the high of say 55%. In the winter they move from the installation average of 45% to the low of say 35%.

When you install your hardwood flooring at the average, each board at the time it is nailed into place takes up the space it needs for the middle of its humidity range. This puts less stress on the hardwood flooring nails and less compressive force on the tongue and groove edges in the summer, reducing the odds of large gaps between boards of hardwood flooring.

I hope this makes sense to you .. but now you understand why I think effective acclimatization is next to impossible. If you wanted to achieve these results then you would have to have the relative humidity in the room where you have spread out all your flooring equal to the average.

Is that possible? Certainly not if this is a hardwood floor installation in January in my part of the world!

Further Information:
Hardwood Flooring Installation Techniques
Hardwood Flooring


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