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Hoping your experience can help figure out where moisture is coming from in my basement. I tried to include a lot of details to help identify issue.

I have a house built in 2008 with finished basement in Northeast Ohio. House has poured concrete outside walls. Inside wall is 2x4 wall sitting on pressure treated plate. There is fiberglass batt insulation between studs and 1/2" drywall on it.

About a week ago, wife told me that there is musty smell in basement and baseboards are turning black. It was mold on baseboards, so I pulled them off and concrete floor underneath was very moist. Pressure treated under drywall looked black and was soaked. I assumed there was a vertical crack in concrete wall so I started opening up the wall looking for cracks (We had 4 top-to-bottom cracks before that I fixed with 2 part epoxy resin). Long story short, I did not find any cracks in the walls, but every cavity I opened up, PT plate was moist with limited amount of mold on paper backer. Concrete side of batt insulation also felt little moist and I think I saw a couple of water drips when opening up cavities. Concrete wall behind batting was moist in some cavities, but dried out in 15-20 mins after opening cavity. Drywall screws & baseboard nails in Pressure treated were rusty as well.

Not finding signs of leakage, I pulled up corner of carpet and there was lot of moisture under padding, but it wasn't pooling. Carpet padding had a plastic top layer. This appears to have blocked moisture from coming up as carpet above was dry and clean. There was some mold on upper side on edges of carpet where baseboard was touching carpet, but no more. Tack boards were badly molded.

I pulled up carpet further and noticed that moisture & mold stopped halfway down each wall. If you look at the drawing, the blue area indicates where moisture was. Past this area, floor was dry and tack boards looked like new (baseboard was moldy, I assume because of wicking).

I think the issue is that moisture gets trapped between concrete wall and batt insulation. Then it makes its way down to floor getting pressure treated soaked and continue under carpet where it permanently gets trapped by padding.

However, why is only this one corner getting wet? If condensation is the problem, shouldn't entire perimeter be wet?

Can downspout be the issue? Ground on side with downspouts drops a foot over 6ft before it flattens out. I always thought that was plenty good. Now, I extended the downspout 4 ft away from the house.

Am I on the right track? Way off? Any help/suggestions would be appreciated.

Basement drawing

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    Check around the window really well, that would be my number 1 suspect. Is there a cutout in the foundation for the window? Is the bottom of the window at, or below grade? If you have the walls open near the window, set up a sprinkler outside to soak the area (simulate rain). Then keep a close eye on the wall, especially near the window (you'll probably have to run the sprinkler for a bit, or wait for actual rain). – Tester101 Aug 5 '15 at 10:11
  • Thank you for your suggestion @Tester101 I set up a sprinkler against one side of the house and 30 minutes later I had a small pond in corner. It looks like majority of the water is entering between concrete wall and concrete floor and minimal amount is entering through expansion cut in wall. Now that source of water is identified, can you suggest solutions to resolve it? – MRAK Aug 6 '15 at 19:26
  • Do you have a perimeter drain, and sump pit? – Tester101 Aug 6 '15 at 19:38
  • There is not perimeter drain on inside (I even wonder if builder put drain tile on outside). I've got a few quotes for installing drain tiles on inside and also waterguard from basement systems. Has anybody have any experience with waterguard? I found it online and am considering installing that, since it is less effort. I am just not sure how effective it is. – MRAK Aug 7 '15 at 0:51
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    Maybe that's true. But where I live, water flows downhill, and nothing is perfectly level. – Tester101 Aug 7 '15 at 2:40
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Can downspout be the issue?

For sure. You definitely don't want the downspout dumping at the foundation line. Ideally you'd have it exit several feet away from your foundation (via an elbow or a splash block or what have you).

Ultimately, the water has to be carried away from that corner of your property. Does your property slope away from that corner or is that a possible place where water is collecting from other parts of the property?

You may need to put in some surface drains to migrate that water to a lower part of the property. I'd also check to see if you can find out how high the water table is on your property. Alas, you can't do much about high water tables.

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WaterGuard was an enhancement to round plastic pipe or actual drain tile as it was shaped to fit on the footing (in cases of monolithic floors a different product would be used). It's been around for about 25 years and is effective and clog resistant as it sits out of the mud on the footer and has access ports for visible checking and cleaning. WaterGuard's channel is 1.5 inches tall, so no slope, to very little slope, is required -- the water will drain as it rises in the channel. That said, there are occasions where lateral connections or an additional sump pump is needed (but typically only in cases of very uneven floors with multiple exaggerated low spots).

  • Thank you @Richard. Would you recommend it or is there any other alternative products that may be better? – MRAK Aug 7 '15 at 20:06

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