My house has 2/3 basement, 1/3 crawlspace. I’m going to dig out the crawlspace and make it basement. The NE corner of the house (this is the crawlspace end) has the grade about 7′ higher than the SW corner (walk out basement end.). I could spend a mint (and kill some big trees) to excavate my foundation installing a “proper” exterior foundation drain (perf pipe, filter fabric, gravel backfill, etc.). Digging externally would be a big PITA (big trees, landscaping, masonry work, buried utilities, etc). I was thinking about breaking up the existing concrete basement floor (it’s cracked and not all that great anyway) and repouring the whole thing over (including the new area in the old crawlspace area). At that time, I was thinking I could build a gravel drainage bed under the concrete floor. It could easily exit in the SW corner and go 50′ or so to daylight (with a generous pitch). I would have NO exterior foundation drains, rather I would give the water a path from my footing to under the basement floor into the gravel.
I hope I’m clear on what I’m trying to do. Any suggestions on how to make this successful?
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I saw a home recently where this was done. The basement is now dry. I'm not certain about the long-term results of this sort of thing. The foundation itself and footings stay wetter with this technique. Are you thinking about going under the footers in some places or just inside the footers? I've seen a lot of basements where there is no practical drain to daylight and the foundation drains run under the footers to a sump where it gets pumped. But, the foundation itself stays drier in that case. I'd think your method is better than no drains at all if outside excavation isn't practical. Only problem is you can't really get too close the footers without risk. If there is much side force on the foundation walls you may have problems if you remove too much or too deep near the footer. Maybe do that part in short sections and backfill as you go?
You did not say, but I would assume you do not have any leaks in the basement or crawl space now?
Aside from your drainage question, here is another question for you.
Have you checked that the footings for the crawl space and basement are continous? Many time, around here, footiing and foundation walls are stepped up where they go from a basement to a crawl space. If that is the case, you have other issue you need to address before you get to the drainage.
If your footings and foundation walls are at the same depth, then adding the interior drainage bed and tile is a good idea. It won't change anything that you have outside now, and will provide hydrostatic relief and drainage should something change outside in the future.
Dave
Both the basement and the crawlspace have substantial water penetration. Crawlspace more so than the basement, but the water just runs to the wall that separates that two and eventually ends up in the basement. Some years ago, previous owner installed interior french drain to a sump pump, which sort of solved the basement problem. I'm gearing up for a major remodel in which I will be putting a second story on the house. The crawlspace foundation is stepped up quite a bit from the basement and crawlspace footings are so bad, they won't support a second story (or the engineer won't sign off on them...) So I'm building two new foundation walls in crawlspace area that are about 3' and 4' out from the existing walls, but I'll be digging them deep enough to eventually match up with basement side. If I can plan on building a drain tile on the interior, I can come up with some way to dump the water from the exterior through the footing and into the drainbed under the floor.
Since you are adding new footings, you might want to look at Form-A-Drain. They are stay inplace forms for the footings that also serve as your drain tile. You could form both sides of the new footing with it and tie it to your new interior drain tile when you replace the basement slab.
I am using it on my new house. Easy to work with after a short learning curve.
I'll try to post some pictures of my footing after I figure out reduce the size of photo files.
Dave
Cool, thanks. I'd like to see some pictures. You can email me fullsize pics if you want, though learning to reduce them is a good thing to know (IrfanView is a free viewer that will do it).