french-drainwaterproofing
My landscaper is suggesting installing a french drain right against the foundation to collect and drain water (I originally proposed just grading and possibly adding pond liner) but he thinks water will collect under it anyways.
Is there a risk this will have more water sitting against the foundation or is this common enough?
Before going through the waterproofing hassle, do check your gutters again. Even though it's the gable end, you want to make sure your downspouts elsewhere are carrying the water away from the foundation as far as they can.
Then, check the slope of the ground. Is it sufficiently sloping AWAY from the foundation? If not, fix that too.
After that, if you still have issues, if you're going to be digging out the foundation, you definitely want to consider a drain tile system while you're down there. That typically has to go near the footer, so be careful doing that (you'll likely want to consult an expert before digging out the footer.)
At that point, the typical waterproofing system is some form of a rubber membrane then covered with dimple-board. The dimple board protects the membrane from the backfill and also acts as a drainage plane into the drain tile system.
I had to draw a small diagram to see how the area was around the house. I drew a swale in to show what is there already, or hopefully something that can be created
What looks troubling here is the concentration of runoff heading to the house IF there is no swale there, that is why I hope there is one there, if not you really need to get the flow away form the house. It is bad enough that it is sandy, the water can still perk into the foundation, though it will be minimized with a swale. The clay base on the north side, sounds exactly as you describe, a bowl.
You need to do whatever you can to minimize the water infiltration, to start. It may not require to pipe the downspouts away from the house to a drywell or into a French drain, well not a French drain as you may plan around the house. French drains return the water to the ground, and in turn the crawlspace. What I mean is terminating the downspouts into an in ground pipe that daylights downhill of the home. A drywell would work too, but it is much more than may be needed.
This is the minimum I would suggest, although it is still a lot to do. I would also consider waterproofing the foundation, it may work on most of the foundation, but I think the runoff would still migrate under the foundation on the south side since it is still on sand/ clay mix presumably.
All of this is still tempered by the symptoms created by the water in the crawlspace. If there is no evidence of black marks (mildew) or white fuzzy stuff growing in places from the excess moisture in the crawlspace, if none of these symptoms exist, al least extreme measures are not needed. Regrade if needed, would be the minimum, downspouts to daylight away from the house the next active remedy, drywell addition the next, and if you are doing all that digging, waterproof the foundation, all these measures combined are the extreme I mean.
Edit 1/26/13
Aside from the shape of the house and other extensions from it, it shows the same thing happening except your swale that exists is more of a collection point. It appears the rain runoff takes the same path, but the house is in the way. The swale in the above sketch I posted would divert the rain water before it gets too close to your home. Is this a possibility to happen? It can be done by lowering the grade or if the house is high enough above grade, the grade can be raised, but that has implications too. The water in the swale may be of no concern. I would draw more concern to the south and west side where the rain looks like it is path is unencumbered to the foundation.
I will edit your drawing to show a more accurate idea and post it.
Back at the downspouts that I mentioned earlier, if the grade looks like it can daylight a underground lead would help reduce the amount of water at the foundation. Yet the addition of the swale will redirect the downspout water as well.
Best Answer
Placing the french drain against the building's foundation wall is common and the correct way to remove moisture from around the structure. Remember, the moisture will be removed down to the "flow line" of the perf pipe. Here, we encapsulate the perf pipe in an envelope of drainrock and place it a few (6") inches below what we're protecting, (I.e.: 6" below basement slab, etc.)
If you move the perf pipe (and encapsulated drainrock) away from the foundation wall, then that allows moisture to lay AGAINST the wall and potentially leak through the foundation wall.