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Moisture Battles

Wayne Lee

My biggest trouble is moisture and getting folks to understand that it is not water or rain, it is relative humidity.  In the South where I live and work we see temps in the high 90s and a RH in the high 80s and low 90s.  Crawlspace cross-ventilation wide open only allows the RH in, and as we know, when the moisture is higher below the flooring than on top the floor will cup. I was in a battle with a local termite company about cross ventilation in a crawlspace for over a year and just this past month they saw the light.

It was a battle to prove that plastic needs to cover 100% of the crawlspace, not just the inside or stopping 1 foot from the wall.  Black plastic is a must to prevent growth under the plastic. Putting RH meters under the house, shutting the cross vents and adding a fan to move air from the middle out has not only prevented high moisture but cupping. A few tricks we do to help our troubles: Coat the plywood subfloor with poly, back-coat the flooring and make sure our RH is under control. It has been a battle all summer long.

If you want to go "Wow," look at the subfloor I put the meter into: 19 % was just a bit high and the wood was 6.6 %. It may take some time to get that wood plus or minus 3%. My wood supplier keeps the warehouse around 70 degrees at 50% RH, so that will help, but this is getting tough to install wood. The hard part is the job site is an hour's drive one way, so it makes keeping track of the site a pain. I am thinking about the programs that can be used online to keep track of all this… 

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