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Moisture content in subfloor

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Sep 05, 2013, 09:32 PM
Moisture content in subfloor
I just purchased a foreclosure that sat vacant in middle Georgia (read high humidity) for at least 6 months. I pulled out the carpet in the upstairs and purchased 3" wide oak flooring to install. The problem was that the moisture content in the plywood subfloor was over 14 percent when first tested (compared to 6 percent for the flooring). Everything I've read says that the subfloor and flooring planks need to be within 2 percent of each other before installation.

It's been over a month of having the A/C running and the subfloors are much dryer than before. I'm using a pin-style moisture meter to measure MC in the subfloor, and now the MC is about 7 percent on the surface, but about 10 percent if I push the pins into the wood just 1/4" or so.

So my question: Where do you need to measure the MC on the subfloor to assure you are in the 2 percent range? I plan to use a felt paper underlayment between the two. Anyone run into this before? Thanks in advance.
Sep 05, 2013, 11:01 PM
Have you read moisture from the underside of the subfloor? Have you put a dehumidifier in the crawl space?

If not, then you are only dehumidifying from the top with the AC in the living space. Stands to reason that if you are dehumidifying from only one side that it will take much longer to dry - and will get wetter the further away you get from the top surface.

Years from now the house will settle into a constant single-digit moisture range. If parts of the subfloor are currently above that then this trapped moisture will eventually work it's way into your new, drier flooring, or cause mold underneath the flooring underlayment.

Sep 06, 2013, 04:21 PM
Is there a crawl space?
If so is there a 6 Mil. plastic vapor barrier on the ground?
Is there gutters?
How is the roof vented.
Sounds unrelated, but there's a reason for the questions.

Sep 06, 2013, 05:25 PM
Thanks for the replies. I did have to pull up a section of the subfloor and read the MC on the underside of the plywood and it was in the 6 percent range, so I thought that a good thing.

This is on the second floor, so not exactly a crawl space, just the space between the floor joists, subfloor and first floor ceiling. There are gutters on the house, but not in great shape (about to get them replaced). The roof is vented with soffit and ridge vents.

It sounds like I just have to be patient and wait for them to dry out. I hope the dryer fall weather will help. Any tips on how to speed up the process?
Sep 06, 2013, 05:39 PM
Originally posted by greyfalcon25:

It sounds like I just have to be patient and wait for them to dry out. I hope the dryer fall weather will help. Any tips on how to speed up the process?

Beyond a dehumidifier, baking soda helps absorb moisture and is especially good for eliminating damp odors. Kitty litter also absorbs moisture.