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humidity 90% in basement

Posted by jarofstars31 (My Page) on
Sat, Jul 25, 09 at 8:44

We moved into a 1940s cape cod in Western PA last year. Right away, we noticed a musty smell in the house and also on our clothing. The basement is huge and a stairway with no door leads to our first floor. The basement has undergone two remodels in its history--in the 1970s and 1990s. Neither of them were done properly to consider a high moisture environment. The sellers disclosed damp walls where visible and they sealed these walls in laundry room and the closets. We have forced air/heat vents down there and invested in a Carrier Infinity HVAC with air cleaner this past Nov. We run a dehumidifier. When it fills and stops, the humidity rises to 90% down there. We have had this confirmed by a digital barometer reading separate from the dehumidifier. We took up the Berber carpet (75 sq yds) and removed it. No mold was found and there was no evidence of water damage to the carpet or padding. Musty smell got better but did not go away. The bathroom was extremely poor construction and with regular use has developed black mold all behind the drywall adjacent to the shower--scary. The floor in here is tile; no water damage visible. We have had a monster summer in terms of storms and rain. No visible water has come into the basement. We have had many people here looking at our basement to diagnose the musty smell; all of them have different solutions. Some want to do exterior stuff, some interior. There is evidence of water intrusion where the floor meets the walls, but this is a 3-4 on a scale of 10 as one waterproofer said. One guy even suggested a internal drain with sump pump, but this seems like overkill given we have no obvious water in our basement. Should we take down all walling and flooring and start over with better moisture proofing methods? Try a Humidex first before removing stuff? The bathroom obviously needs to be demolished and start over because of the visible mold, but what about the pine paneling? We do not know who to trust here, because of the different opinions. Gutters work fine. Grading could be improved. A large deck covers the back corner of our house, so that we cannot see.


Follow-Up Postings:

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RE: humidity 90% in basement

We run a dehumidifier. When it fills and stops, the humidity rises to 90% down there.

And when it's running, what is the humidity level? If it falls to 50% or less, there's your cure.

The musty smell is no mystery. It's from the mould growing in the humid conditions. And, also, don't open the windows in summer to let fresh (humid) air in.

When you rebuild the shower, include a powerful exhaust fan near the shower that is wired to run whenever the light switch is turned on. That way, no one forgets to turn it on.

I assumed you are in a mixed or cold climate. For hotter more humid climates, more of the same applies. See link.

Here is a link that might be useful: Supplemental Humidity Control for hot-humid climates


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RE: humidity 90% in basement

That is a very good idea regarding the exhaust fan and the light connection. I'll read the link right now. Even when the dehumidifier runs, it only gets down to about 65%.


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RE: humidity 90% in basement

If possible, attach a hose to the dehumidifier and run it directly to a drain or sink basin so you can run it continuously. If there's a floor drain or one outside of the bathroom anywhere, great. You may have to elevate the unit. (I suppose you could even run the water to a small AC condensation pump and send it outside with tubing).

As for the mold in the bathroom, check if there's an internal source of moisture (other than shower steam). For example, the shower arm might be dripping behind the wall (a simple fix, if so). Water can also get behind the wall near the trim kit surrounding the handle.

In any event, I'd remove the damaged material, run water, and inspect very carefully for leaks and/or water intrusion during rains. Then go from there.


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RE: humidity 90% in basement

How much work is it to improve the grading? If it isn't that great I would do that. Poor grading can cause all sorts of problems. Is it possible to remove a board or something so you can examine the conditions under your deck.
Depending on the size of the dehumidifier and basement maintaining 65% may not be too bad. You usually can do some selective material removal to examine what's behind a wall without causing too much damage.


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RE: humidity 90% in basement

I wonder if you have water under the basement floor? That would explain the high humidity. Moisture leeching through the concrete.


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RE: humidity 90% in basement

Concrete holds a great deal of moisture, some of it permanently as "water of hydration". But beyond that, the excess moisture is released slowly to an atmosphere that is relatively dry. My new house basement was about 70 -75% relative humidity with no water intrusion. My two dehumidifiers ran quite a lot for about a year to keep things at 50%. Since then for 3 years they run infrequently.


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RE: humidity 90% in basement

I would run the dehumidifier into a sump or other drain so it doesn't need to be emptied (what a pain that must be) and I would make sure the dehumidifier is sized properly for the space. Does the bathroom have it's own fan? It should. Personally, I wouldn't mess around with the exterior if you've already don't the basics (gutters that drain away, grade is pitched away from the house). You might have a spring under the house (we have one). Try to control the humidity with a properly sized and drained dehumidifer and put the bathroom fan on a time (we have one that lets you select 20, 30 or 60 minutes).


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RE: humidity 90% in basement

I would use a dehumidifier since the Humidex product does not work. Save your money and purchase a dehumidifier at a fraction of the cost.


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