I have a 3 story rental unit with 4 apartments. The apartment on the middle floor reported that the closet wall was wet. When I checked it the wall had mold and a moist/wet feel to it. The ceiling and other walls seemed to be dry. This is an outside wall so I thought there was some type of leak behind the wall. I pulled the sheetrock to to find that there were no pipes. The outside of the house is cinder block and I discovered that the sheetock was screwed to furring strips, no insulation.

I checked the outside, no obvious cracks in the paint or holes in the wall. The nearby old window was a bit wet but there didn't seem to be any moisture on the wall under the window or to the side wall. I thought perhaps the water was somehow penetrating the block so I used drylock to seal the wall, 2 coats, added some foam insulation and sheetrocked with greenboard.

The tenant just called, 5 weeks later to say the closet was very wet and moldy. Apparently they do not use the closet very often. Above the closet are stairs heading up to the 3rd floor. There did not seem to be any moisture on the stairs when I checked.

So how do I find the source of this moisture? Especially when I don't live there myself so I can check it daily. Any advice or ideas are greatly appreciated.

  • it may be a roof leak traveling down a rafter then down the wall. (i know you said middle floor)or a leak from the top floor that is traveling down the stair supports. I would reccomend finding an energy auditor. they can take IR photos that can see leaks through the walls if they have the latest top end cameras. we used this method to find a leak that was traveling over 25 feet from the source and we could not find it. I believe the extra photos we needed cost us about 50$ but saved us from tearing out a lot of sheetrock and days of work to find the leak. the pics will need to be from inside
    – Ed Beal
    Dec 10 '15 at 0:20
  • Are you in a climate where it's warm inside and cold outside? Are your tenants creating a lot of humidity (ie, drying laundry inside) without opening windows? Closets have very little air circulation, so could grow mold in this situation. Dec 10 '15 at 13:53
  • Thanks Ed, I will keep this idea on the back burner for now. My concern with bringing in an energy audit company is the up sell. This is an old house with lots of areas to improve energy efficiency, but it is a rental property. Dec 14 '15 at 13:51
  • Thanks Aloysius, There are no dryers, and I have considered this possibility since they do have a fish tank. However, there are no issues in that area of the apartment, the tenants have been there for over 4 years, and this is a recent problem, so I really think there is a leak somewhere. Dec 14 '15 at 13:53

Minus any pipe leaking, the only other sources is roof/gutter leaks or condensation due to temperature differences (both mentioned above). Based on the amount of water you’re mentioning to complexity soak the walls is sounds like you’re dealing with a rook leak. Get a reputable roofer to find the source and get it patched. If the roof is already pretty old it may be time for a new roof and less headaches into the future! Good luck.


you can run a dye trace on the building. you just buy a uv trace kit and you add the different colour dyes to the suspect areas. then wait a couple of days and check the area with the uv light. whatever colour shows up is from the site with the leak. you may have to repeat a few times to get it to show up.

as an aside, if its a flat roof, check the adjacent areas on the roof really closely. its often the case that you will get a hairline crack in a sill or dam and its the cause of the problem.

  • Thanks for the idea. It makes a lot of sense and I do believe the source is a leak that occurs when it's raining. It's raining today so we shall see. I will update here to let you know how that works out. Dec 14 '15 at 14:11

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