Poorly maintained 1960s 2 story house with fin. basement. 18 mos. ago installed 2 dehumidifiers to knock down mildewy smell that (this being Portland, OR) had probably been there a long while. Also sealed up all dirt crawl space (per TFB’s good article on this in Feb/Mar 2003); smell back to normal after 2 mos or so, kept running the dehumids. for another year. I expected this to shrink up the hardwood flooring on the first floor a little, which it did…but we have some nail popping & seam telegraphing at some drywall? Even ceiling trim has shrunk in a few places. Repainting in spring, so not a huge deal, but I was surpised at this. Possible to have that much ambient moisture pulled into the walls? Thanks,
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I can't offer any real
I can't offer any real technical advise, but I would think that you should know and understand what the humidity is and should be in the structure.
Brian,
Since you sealed the crawl and limited moisture moving up into the joists and subfloor, and then ran the dehumidifier, whether down there or in the dwelling-yes it is possible. Most of the shrinkage will take place in that crawl framing-joists will shrink in width, the subfloor also will move. Plates and studs not so much, but with the whole underneath moving-cracks, pops and so on would be probable.
Normal winter humidity should be around 35/40 to keep finishes, furniture and your nose in a moderate equilibrium. There's a guy that used to be around here from Portland that would be more locally knowledable. I'll see if I can hunt around and alert him to this post.
you usually should not be dehumidifying on a year-round basis
get a moisture meter and check the moisture content in your floor and attic framing... i like to keep it above 12
and your indoor air quality at about 40 % RH
Thanks guys. Good comments. I'll go get a moisture meter, do some checking @ different stud locations, and also get a little more thoughtful about locating the dehumidifier & when to operate it. But even running it 90% of the time in the finished basement we still never can get RH below 50%.
Brian,
I live some 40 miles
Brian,
I live some 40 miles south of you.
My indoor RH during the winter months stays about 45% in the heated sections of my house and a bit higher (50-53%)in some unheated or minimally heated sections.
No dehumidifier used at all.
No basement, house is a early seventies wood frame over crawl. Vented crawl is covered with plastic (vents closed during the winter), floor is insulated. House has been tightened as much as economically possible.
I think you are dehumidifying the house as a whole too much .
My experience is that you almost never need a dehumidifier in this climate during the summer months and even in the winter in a tightened house (depending on heat source & lifestyle,, wood heat actually needs humidification and lots of indoor plants showers without vent fans etc.means you do ) they aren't necessary.
I would guess that after sealing off the dirt crawl you are getting excess moisture into the finished basement through the concrete or block walls.
Check the downspout drain system (assuming you have gutters) for slope/leaks and outfall and check your grading at the basement walls.Look for any signs of actual moisture penetration in the basement ( I doubt you have a vapor barrier under the slab in a house of that age here, the practice of installing vapor barriers under slabs didn't come along until after the date of construction).
All that makes a lot of sense. I may be opening up this "finished" basement in a few years...
Thanks for the response.