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craiger4233

sudden subfloor condensation problem

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My issue:  Wood sub-floor suddenly staying wet with between 17%-24% moisture and the old peel and stick floor tile has come unglued. Cant lay new tile until sudden moisture problem is solved. This is the first time we have had any sub-floor moisture problems in this home we have lived in since '73.

 

House description:  1945 block and beam, 835 sq.ft., walls and floor not insulated, minimal bat insulation in ceiling, attic has large gable vents and two whirly bird vents with closed non-vented soffits.

 

Recent changes:   6 mil. poly sheet on crawlspace ground well ventilated and moisture free.  Added 1-1/5 ton ductless heat pump/ air conditioning to the room that is having the issue and using the ductless unit as the main cooling for the house with one window unit used occasionaly to help circulate the air. Two weeks ago we set up a 70 pt. per 24 hr. dehumidifier in the room with the ductless and wet sub-floor. The dehumidifier has ran at full capacity the entire time. And I recently added two L walls in the attic to add support to this old 7/12 pitch roof.

 

I have done a lot of research and I have my personal evaluation but this old woman will not believe me. She seems to wish to believe product review websites and whatever she can find on the internet to my hard work researching building science. Please advise.

Edited 10 minutes ago by craiger4233

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The crawl space is not "moisture free," it may be "dry" but is at ambient exterior conditions.

 

Sounds like the new air is too big. The dehumidifier can't address the newly chilled subfloor and condensation there.

Try a box fan in the doorway to move more of the cold air to the rest of the house. What temp are you running in the room?

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She is keeping the mini-split set at 70 usually and sometimes 68. I am getting a humidity monitor and room thermometer to test the what the actual temp. and humidity is in the room. But you are on the same page as my evaluation. I am just uncertain what to do to solve the problem.

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Brr that is cold. The dew point is occurring in the subfloor. You could try adding fiberglass batts under the floor and move the dew point away from the wood. Or seal off the crawl space and condition it. The minisplit if running most of the time should dehumidify the room properly. If short-cycling, its way oversized and doesn't run long enough to take the moisture out (in the room).

 

Or add heat strips under the subfloor, or install one of those New England circulating warm water floors.

 

Internet reviews don't usually address gulf coast moisture problems properly.

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Where's the condensation water from the mini-split going?  If it's just falling on the ground under the unit than you're adding to the humidity right there.  If that's the case, you might consider installing a drain of some kind to get the water away from the house.

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