Water leakage - external concrete overhangs interior ceiling 1

[BT71]

I'm working on an entry door water leakage problem into a basement. Home is 1997 design and construction. Builder is apparently out of business already. [blue]I need some design ideas about what to do to really fix this.[/blue]

The best description is to look at a picture, and a cross section: DoorPix The red "X" indicates the portion of the external stoop that is overhanging the basement ceiling.

Otherwise, the description is as follows: the entry door threshold is some 24 inches inboard of the poured wall foundation. Visualizing that, the door was placed over a doubled joist cross beam, the stringer joists were cut in half and the bottom portions used to extend out to the foundation wall, an OSB panel was laid on top of the cut down joists, tar paper on that, and concrete stoop poured over that. Well now it leaks from time to time, which is inhibiting a basement finishing project with drywall and texture ceilings. I've never seen anything like this in the field before, hoping someone else has.
Assuming a willingness to take out the stoop and make a better design, what suggestions would you have?

 

[JAE]

First off, depending on your particular jurisdiction, and applicable code, you may have a code violation in that most codes prohibit supporting concrete with wood. So you may want to consider an alternative detail here as the long term consequences of wood getting rotted by the natural moisture in concrete, and perhaps other sources of moisture getting into the concrete, can be disasterous.


To waterproof, you could use a traffic bearing waterproofing such as Pedagard by Neogard, Inc.

http://www.neogard.com

 

[BT71]

Hello JAE,

Thank-you for the reply, I agree it may be a code violation and needs some research. I haven't sampled the concrete to see if any re-bar or other support is cantilevered over the interior ceiling such that not all the load is on the wood.

I think anything is possible in this situation - from giving up some basement space by adding foundation underneath the door down to ground - to ripping out the offending stoop, fabricating a real support structure and sealing it from moisture and then repouring the stoop.

Where I am stuck is on that second what if ... assuming the basement space underneath the stoop has to stay, then what kind of design would be viable assuming anything goes? Can it be as straighforward as a metal box on top of the wood box, sealed, and then some metalwork inside the new stoop?

 

[JAE]

I do recall that some codes have revised the concrete-on-wood issue such that "topping" slabs may be allowed....do check into it.

Most waterproofing details (beside the link I included above) utilize a kind of rubber membrane beneath the concrete. In other words, you let the concrete leak (it will through cracking anyway) and detail the membrane such that the water is successfully directed away from the building and out to a place where it can migrate away properly. Check with a local roofing/waterproofing company in your area to see - or call an architect as they usually deal with waterproofing specifications and details.

 

[Ron]

The "waterproofing" you described on the OSB is grossly inadequate. Code allows a topping slab as JAE mentioned, but the substrate must be adequately waterproofed as the concrete is pervious and does not adequately inhibit water intrusion.

The condition you descibed has to be treated essentially in the same manner as a shower pan would be constructed in a 2nd floor bathroom. Complete waterproofing (using a "built-up roof concept" or one of the better "peel and stick" waterproofing membranes)must be done (including turning the waterproofing membrane up the sides an adequate distance...usually 8 inches) and the concrete added for wear protection, fill, and aesthetics.

You mentioned you want to "really fix this". Tear it out down to the OSB, replace the OSB with good quality pressure treated plywood, create a waterproof "sump" using proper waterproofing materials (then test it for watertightness) into which new concrete topping (preferably lightweight structural concrete or gypsum concrete) is placed.

 

[BT71]

Hello Ron, JAE,

Thanks for your reviews and comments, time passes quickly but not quite there on this one yet. It took a few calls and e-mails but a local architect was employed and design drawings are due this week. The expected solution is just as you describe, just need to run it by the local permitting office to make sure no mistakes are made and then do the work. Will advise any further discovery.

The one problem I do expect to find is that the architect will say the solution is leakproof only in the case where the membrane has no penetrations. From a practical point of view, when a membrane runs up under the siding several inches and in all likelihood also folds over the threshold plate and is sandwiched from above by the door threshold, I don't quite see a way not to drive a few nails or screws to secure the lower siding of the door threshold. Any advice on contruction without penetration or other belt and suspenders sort of sealant around those few punctures?

 

[Ron]

Make sure any penetrations are above the water plane (top of concrete plus a little "safety" factor. As for the threshold, make sure the membrane extends under the threshold, then set the threshold in sealant before penetrating with screws. Use butyl rubber sealant, not silicone.