As my hardwood flooring project has drawn closer, I have been lurking at this site, reading all I can. I'm very impressed by the amount of knowledge here.

I live in Tempe, Arizona (a suburb of Phoenix) and this time of year is known as our "monsoon season". The winds reverse and instead of the bone dry air we get most of the year, we get moister air blowing up from Mexico. For most of the year, our dew point is between 15 and 30 degrees, with corresponding RH between 5 and 15%. In July through September, our dew point is 55 - 65 degrees and the RH is more like 40%.

My 3/4" x 3 1/4" T&G prefinished maple will be here on Saturday. Since it's coming from the east coast, I'm going to let it acclimate for two weeks. Do I need to worry about the fact that we are in our humid season right now? I'm going to override the automatic thermostat and keep the area where it will be stored and installed at a constant temperature. The A/C removes humidity when it runs, but is that enough? Should I wait until the humidity drops?

Thanks in advance for your advice!

-Chris

Is the flooring going on a slab, crawl-space, basement? The moisture in the air and under the floor should both be considered.

The flooring is going in on the second floor over a 3/4" plywood subfloor. The house was built in 1973 and has been occupied continuously, so, barring any leaky pipes, the subfloor has stabilized as far as moisture content is concerned.

I am going to buy a hygrometer to measure the RH inside, but I can tell by the fact that my glass of ice water is sweating, that it is more humid than typical.

I know that most of the experts on this board recommend about 40% RH inside year-round. That's just not going to happen out here in the desert southwest. I have seen dew points in the negative with RH in the single digits.

I guess my question is about whether I should be concerned that this is the more humid time of year. Right now, my house is 79 degrees, and probably 25% RH. Is there a threshold beneath which wood is considered "dry" and doesn't change size with small humidity changes?

Thanks again for the advice!

-Chris

When your maple arrives (open at least the sides of the boxes, if you have the room rack out as much of the wood as you can without installing) check the moisture content of the wood, check it every day until it is neither gaining or losing moisture, when this happens your wood has reached its equilibrium moisture content. This does not mean it is not succeptible to changes in rh inside your house.. What is the rh inside your house going to be when things return to normal? You said the temp was 79 and the rh was25% that equates to about 5.3%. If in the future the temp is still 79 and rh is 10% that equates to 2.4% and based on the dimensional stability of maple you could have shrinkage as much as 1/20of an inch.

Hope this helps. You can check the US DEPT OF AGRICULTURE WOOD HANDBOOK and check the equilibrium moisture content chart. It is listed in "Wood Handbook-Wood as an Engineering Material."

Waiting for the moisture content to stabilize while being acclimated makes sense. Then, the wood will "match" the current climate in the house.

In general, where we have reliable annual changes in humidity, is it generally considered better to install during the moister time of year or the drier? I can see downsides to both:
If installed during the more humid time of year, the wood will shrink during the drier times.
If installed during the drier times of the year, the wood will expand against the adjacent boards. From what I have read on this board, a small amount of expansion could crush the fibers of the wood, causing it to leave gaps when it subsequently dries. A bigger expansion could cause bigger problems.

Obviously, with wood being a natural product, it will always be responding to the environment to some degree. I just want to make sure that I'm not shooting myself in the foot by installing at one time of year or another.

Thanks for the help!

-Chris

Try to counter extremes in rh with humidifiers or dehumidifiers depending on which makes sense. Always have an accurate hydrometer running to guide you. If you can keep the rh withing 10% year round you should hardly notice any changes. Don't just keep the hydrometer in one place. If possible use more than one.

Also you are installing a wood floor, Until recently It was understood that wood floors had cracks. With the wide swings in humidity you will probably have some cracks.
Its not the end of the world. You just look at them, shrug your shoulders,
and go back to what your were doing.

If it really freaks your out you can have an inline humidifier installed directly into your furnace/ac unit. Its a little spend but not much more then a good washer or dryer.

Boise has humidity swings similar to yours , We get very dry in the winter because of all the forced air heaters and sometimes we get inversions that keep the daily high below 20. That makes for a long heating cycle on our furnaces.

Hope this helps alittle.

Steve

I am *not* an expert at all. But let me pass on my experience from El Paso. We have a similiar climate and our house has swamp coolers. Needless to say we have major swings in humidity. I'm not sure I know the answer to this situation, but seriously educate yourself or you *will* have issues. And don't necessarily trust the contractors... not that they don't mean well, but sometimes they are simply cutting corners that doesn't cause a problem for most of their clients... but you might just have that *special* house!

Good luck....