Exterior waterproofing of foundation wall and footing
We’re getting to the point of waterproofing the exterior of our foundation and installing the french drain. The waterproofing is going to be one of those sprayed on membranes.
Typically I see pictures of the french drain placed outside of the footing at the same level as the bottom of the footing. However I’m being told that the new way to do the french drain is to sit it on top of the footing. The reason being that if water ends up sitting on top of the footing it has nowhere to go and has more chance of penetrating into the house. They’d still fill gravel around the outside of the footing and above the french drain.
The other thing I was surprised at is they tell me they only waterproof the wall down to the cold joint between the wall and the footing. I’m surprised they don’t waterproof the seem between the footing and the wall. Won’t water seep in between the joint even with a capillary break?
Luckily I insisted on a painted on capillary break between the footing and the wall and secondly my interior slab is at least 1 foot higher than the top of footing.
Two questions:
1) Is it okay for the french drain to be on top of the footing?
2) Is it okay for the joint between the footing and wall not to be waterproofed?
Our soil is very dense and clay like.
Cheers,
Steve
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Replies
HI Steve -
Locate the drain at the level of the footing. This will drain the water for the entire assembly: footing and below-grade wall. Trying to address the cold joint between the footing and the foundation wall by locating the perimeter drain on top of the footing is misguided.
Waterproofing the cold joint is simply tough. But waterproofing it is definitely a good thing to do while you are down there. True waterproofing--NOT dampproofing--has some self-healing ability should there be any movement at this joint. So make sure your membrane is waterproofing and not dampproofing.
The only way to be certain about keep water out of the cold joint is a waterstop, but that horse is out of the barn in your case (see: https://www.greenbuildingadvisor.com/article/petes-product-puzzle-cetco-rx-101-sika-703).
Just my opinion, it probably doesn't make a difference. In my area I know there are guys that successfully install the drain on top of the footing. And around here the footing is often below the seasonal water table depth of 2-3 feet.
One advantage of going on top of the footing, is that it's fast and and really hard to mess up.
Also if you backfill the trench with a foot or two of stone, the whole thing's gonna drain either way.
Yeah it is already to late to put it around the outside of the footing. They installed the french drain on to of the footing probably while I was writing my question. The good news is that they seemed to do a very good job of water proofing the concrete.
The french drain is a little different to what I expected. It is about 6" tall and about 1" thick. It looks like it is some kind of plastic dimple material wrapped in fabric. Does anybody have experience with this kind of drain?
Steve