Split level slab floor

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I was thinking of dropping half of my concrete slab floor to make it one step down. But before I do the down portion, it dawned on me that it might leak water from the top level to the bottom. The grounds a gradual slope and plastic has been layed on the ground before the concrete pour. What do you think, risky? Anyone have a slab floor leaking problem? Am I making sense?....Kirk

-- Kirk Davis (kirkay@yahoo.com), November 29, 2000

Answers

This is a common building technique and I have heard of anyone having a problem.

-- Ken S. in WC TN (scharabo@aol.com), November 29, 2000.

As Ken says, it is a very common technique. Here in the Southwest, the town "yuppies" like split level houses. Yes, it does rain and rain hard at times. I have never heard of a problem. Of course, you could use drain tiles under the upper levels if you are concerned.

-- JLS in NW AZ (stalkingbull007@AOL.com), November 29, 2000.

is this in a house, barn, garage or what?

-- STAN (sopal@net-port.com), November 29, 2000.

Stan: I'm adding on a bathroom kitchen. The split would be the wall between the two. It would be a disaster if water leaked down to the lower level. Maybe I'm just being paranoid....Kirk

-- Kirk Davis (kirkay@yahoo.com), November 29, 2000.

cutting ANY inside concrete is tricky, remember, the slope is in there for a reason, so getting rid of part of it, might mean trouble. But doing anything is possible,, consider if its worth it. If you are going to do it,,, I would waterproof the heck ouot of it,, just to be safe

-- STAN (sopal@net-port.com), November 29, 2000.


Kirk, my house has three levels of slab "downstairs". I'm in Oregon, it rains a bit here :), and the house is dug into the hill on the uphill side. I put the equivalent of "French Drains" on the uphill side of each level. Used three inch perforated flex pipe, which is perforated with fine slits all over the place. The pipes are slightly lower than the next lower floor, and buried in pea gravel. Also, all the slabs are underlain by at least three or four inches of pea gravel. Over the pea gravel is six mil visqueen. Each perf pipe runs slightly downhill to daylight below the house. The first winter after we moved in we had sixty-five inches of rain. Never have had any problem. This technique is not unusual here.

I'm a builder, and have corrected problems with the scenario you refer to, when improperly done. One house had water coming out from under the upper slab, and filled the lower slab room (which was the living room) as much as two inches deep. I had to put a five foot deep french drain all the way across the width of the house, on the upslope side. This cured the problem, but was very labor intensive. It's best to do the work before the slabs are poured.

JOJ

-- jumpoffjoe (jumpoff@echoweb.net), December 01, 2000.


Sorry, I didn't make it clear about the visqueen: it's UNDER about three inches of pea gravel. Having the pea gravel directly under the pour helps keep the slab from cracking, and gives the excess "cream" you get from tamping and floating the concrete a place to get away, making the concrete a bit stronger.

JOJ

-- jumpoffjoe (jumpoff@echoweb.net), December 01, 2000.


JOJ: I have a problem with draining the upper level because I have already poured the foundation 2 ft by 2 ft. Guess I should go ahead and just pour it flat and build the low slope up with large rock. Thanks for the tip on the pea gravel. I wondered how to get my concrete to drain. I've been pouring right on top of plastic. By the way, thanks for Skeptic.com. That is a fun site!.....Kirk

-- Kirk Davis (kirkay@yahoo.com), December 01, 2000.

Glad you liked the skeptic site, Kirk :)

I don't know your situation where you're building, but could you extend your slab a foot or so, then drop to another level? This would allow you to put in a drain buried in pea gravel. If you do this, be sure to drill the existing slab with, for instance, a three eighths inch rock bit, and set a piece of #3 rebar into it every two or three feet. This will keep the extended slab even with the old slab; it will be unable to settle this way. (I'm assuming that this will not be under a bearing wall, so as to eliminate the need for a footing in this location.)

JOJ

-- jumpoffjoe (jumpoff@echoweb.net), December 05, 2000.


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