basement water mystery

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There are over 12,000 hits on basement water in alt.home.repair. But I couldn't find anything that quite matched up with what I'm facing. We've had water appear in the basement guest room twice now. Once one year ago, once last week. And I seem to have ruled out all possible sources...so I must be overlooking something.
When the water appeared a year ago, it was so strange that we figured one of our teens must have tried to empty the dehumidifier and spilled it, though they swore they hadn't. But now the same thing has happened and the dehumidifier isn't in that room.
FACTS:
1) The house is a raised bungalow, so the basement floor is only about five feet below ground level. The guest room is in the corner of the house opposite the main basement drain. It's also far away from the city water line and any other water lines that we know of. 2) The water appeared centred about 4 feet from either wall, so wasn't in a corner nor smack in the middle of the room. One of the aforementioned walls is exterior, southeast side, the other is interior and load-bearing. 3) On the other side of the interior wall is an unfinished work room where we can check ceiling joists and see bare concrete block. Bone dry in there. 4) After a couple of days (we found the water on Tuesday) the water had spread in a circular pattern. We had a fan and the dehumidifier in there by then. 5) Upon lifting the carpet and pad today, I was able to determine that the apparent origin of the water is the local high point in the floor. My carpenter's level says so, and pouring a bit of water on the floor underneath shows that it all flows away from that point. Water poured nearby will not flow up to that point. 6) The old floor is 40+-year-old asbestos tile, bonded down like nobody's business. 7) No sign of water from the ceiling. The dining room is above the guest room. 8) Our basement flooded (as did many people's) after torrential rains in May 2000. I put in new drywall and made sure to have vapour barriers, sealed joints between walls and floor, and venting of the air space behind the drywall to fight condensation build-up behind the walls, just in case. So I can easily check behind the walls. Dry, dry, dry. 9) During the 2000 floods, our main problem was a crack in the concrete in another area of the basement where a wall had been taken out, probably by the original owners in the 60's. Hydrostatic pressure was pushing water through the crack like a tiny geyser. We had the crack repaired. We also had the downspouts rerouted to run out to the lawn, at least 12 feet from the foundation, instead of into the weeping tile system, which is 47 years old. 10) We're in the midst of the hottest and dryest summer on record here.
My theories are:
A) Our kids are malicious liars. B) The water came through the foundation walls, flowed uphill, dried itself off the walls and the carpet through which it came, then flowed back out from its rallying point. C) We have hydrostatics troubling us again despite near-drought conditions.
I am perplexed. What am I overlooking? What fundamental thing do I just not understand?
Thanks for ANY ideas!
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snipped-for-privacy@home.com wrote:

lot more to compensate for the drought? The water might come from there, somehow.
Perhaps you could use a die on the lawn to track the water source
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snipped-for-privacy@home.com wrote:

You fixed hydrostatic pressure by patching the floor??? no seriously?
You could have a roof leak, especially considering its a bungalow. We had a roof leak that showed up in the basement in a colonial.
Is your carpet covering on of your floor drains? The foundation drain connected one perhaps?
You can always stake out the basement :)
--
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CL Gilbert
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I should probably answer some of the other questions here, all together:
No cat. One dog. Several litres of liquid at least. The liquid doesn't smell like urine, though, just water.
We and everybody have been watering less because of the water shortage. Our neighbours on that side have been gone for weeks and we're doing limited watering for them.
No pipes under the floor that we know of. We have forced air heat. No drains in the area.
"Fixing hydrostatics" ... LOL. Well, I didn't really fix the hydrostatics....just the problem of it coming up through the crack :-) .. I figured all I could really do was convince the water that it wanted to go somewhere else. "Roof leak"....I'll look into it. A couple of our shingles needed replacing, which I did today, and they are over that room. But leaking all the way past the main floor and down to the basement?
No drains nearby, unless the builder put a second one in (the drain we know about is in the laundry room, other end of the house) and then some handyman covered it over with tile.
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I bet it is the roof leak. When my wife was in college, she was in the first story of her 2 story apartment house. Her roof leak. I had a flashing problem in the current house. The water went thru the wall down to the basement without any damage to the wall. I could hear it dripping though.

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snipped-for-privacy@home.com wrote:

Yes, I had a leak do just that. And early roof leaks can be tricky. They can require rain to fall in a certain direction for enough water to reach the basement to be present. Next rain, whenever that is :), check for it. But you may not see it due to directional issues.

Thats how my last basement was. We lived in the city so we had a full city setup. Sewer feeding floor drain was in the washroom. We had a 2nd floor drain that fed into the foundation drainage system which feed into a storm sewer I suppose. If that is clogged then you may only see a few days after a rain.
Time for a stake out. Get a camcorder.
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CL (dnoyeB) Gilbert wrote:

All you folks have been extremely helpful and given me a lot to consider. I'm going to monitor for water welling up or condensing out for the next several days. (We finally had a big storm Friday, which might speed things along.)
Next step after that, I think, will be to pull up the tiles in that spot and check for evidence of a covered drain. Can I use a propane torch to soften the tiles to remove them? They're asbestos, I'm certain, and they are bonded TIGHTLY.
Also, would one of these new subfloors that have the pimpled plastic barrier underneath work if this is just an occasional problem? We were planning on remodeling much of the basement this fall and winter anyway. We could put this kind of subfloor in everywhere so that any water build-up would work its way between the plastic pips downhill to the laundry room drain. Does anyone know what this stuff is called? There's one kind - I think it's black - that comes bonded to squares of subfloor, and another kind in orange rolls where you put separate ply subfloor over it.
Or, is there a vapour barrier or treatment that will definitely work if it is seepage up from the floor?
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Update: after 36 hours the suspense was killing me, so I checked under the plastic sheeting I had taped down around the prime trouble spot. No moisture, not the slightest hint. Absolutely, totally dry. Not cold either, just cool to the touch like any tile floor.
Hmmmmm.......
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Thanks for the update. Any rain in the forecast?
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Edwin Pawlowski wrote:

Not really. Nor has there been much at all, all summer. Last Friday we had our entire allotment for August fall in about 3 hours. But that was three days after we discovered the water. There had been "almost" no rain prior to that.
("Almost" is relative. This is Toronto, not Tucson.)
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Do you have a cat?
Seriously, how much water are you talking about.
One thing you can do is to tape down plastic to the floor in a few areas and see how much mositure shows up over night.

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D) Alien space ship fueling site.
Does sound strange. Any pipes running under the floor? Do you have hot water heat? If so, did the installer cut corners years ago and run a pipe under the floor?
Drains running under it?
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snipped-for-privacy@home.com wrote:
I suggest that you may have more of a natural ground water problem than you think.
First step is to test to try and determine where the water is really coming from.
Go to the area where you had the problem. Tape about a foot square of plastic or foil onto the floor. Come back in 24 hours (morning would be good) and take a look. Is there moisture on the top or under the foil or plastic? On top, means it is the humidity you need to work on. Under means it is coming up from under the floor.
Ground water can be funny and may be very close to the surface on one spot and a couple of feet away it may be much lower.
That high spot makes me wonder. I have not seen it, but I wonder it might be the result of natural water pressure at that point? Drilling a hole there might help you tell, but it also could start a bigger problem than you have now.

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clipped

I must have misunderstood something. The wet spot on carpet is high point of the room? Stain or mineral deposit on wet area, signifying long-term moisture? Now that the carpet is up, lay newspaper down over entire floor and check it daily for moisture. Is their a ceiling fixture in the room above wet spot - a leak upstairs that could traverse a pipe, beam or wire and drip out through fixture?
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Norminn wrote:

The fixture is a few feet to the side, in the dead centre of the room. No stain or deposit to signify long-term moisture. Yes, it's at least the local high point and it feels, as I walk along, like the high point of the room overall, but I don't have all the carpet up yet to be sure.
Several of you have recommended checking for moisture buildup while the carpet is up. I will do that. Which do you all figure is the more effective test: plastic taped down over the suspicious spot, or newspaper over the whole room?
Thanks to all for the suggestions.
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Set up a video camera to record overnight..
see where the water comes from.
Mark
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did you check for a cold spot in the floor, where water vapour which is in the air, is condensating?

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jan siepelstad wrote:

The floor doesn't seem colder there than anywhere else, but....
Up until just a day or two before we discovered the wet spot, it had been very warm and humid, almost without a break, for several weeks. Does it sound possible that the humidity in the air penetrated through the carpet and the pad, contacted the tile-on-concrete floor, and condensed out? In this scenario the fact that it's at a high spot would be irrelevant; the main issue would be that it's a cold spot. No one was in that room for several days before the discovery, maybe even a week.
Hydrostatic pressure is also still a prime suspect, but jeez, it was so dry here all summer! Could condensation have happened as described above despite the barriers of the carpet and pad?
Also...if it is hydrostatics, is there some kind of sealant or barrier I can use to block the water...without having it come up someplace even less convenient?
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snipped-for-privacy@home.com wrote:
Thinking about this a little more I have two ideas.
I think the comment about the roof like may be correct. They tend to show up in some unexpected places.
I would also wonder if there was a cold water pipe or an A/C duct or pipe above that area. Keep in mind that you don't always see discoloration.
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Joseph Meehan wrote:

If somehow the water is running in from a wall and pooling there, then it may be. Maybe the wicking action of the pad is stronger at the collection point, thus causing water to effectively flow uphill.

Wouldn't the ceiling, which is acoustic roll-on, be wet or softened there? It's only a 7'6" ceiling so I can reach it with my fingers. I don't feel anything there.
The condensation idea mentioned by Jan may also have merit. It has been warm and humid, though with almost no rain (until a couple of days ago). We have been using our air conditioner a lot this summer. Although last summer we hardly used it at all....
What if I can't find the source of this once-a-year-or-less problem? Do I just put a vapour barrier down beneath new pad and re-lay the carpet? Is there some other remediation measure I can take that will allay the symptoms if not completely prevent the problem? Is there a different floor I could put down?
Thanks so much for your ideas, everyone.
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