crawlspace french drain -- would it weaken the foundation?

I asked a few crawlspace waterproofing company came to look at my wet crawlspace and they all suggested a system similar to a french drain around the inside perimeter of the foundation wall. It would terminate in a sump basin (bucket) that contains a sump pump with the output connected to a storm drain.
Since the foundation is resting on soil, wouldn't digging a trench in the soil near the footing weaken the soil's lateral support and lead to settlement (sinking)? They would fill the trench with wash rocks but still it would not be as densely packed as undisturbed soil.
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That's standard. The trench that they dig is only 4-6" deep, and it won't affect the foundation. Basically, they are building a little gutter just inside of your foundation walls. I had this done on a house I renovated once, and it worked great in conjunction with some other actions:
1)Be sure your gutters are clean and that water isn't rolling off of your roof and sinking into the ground near the foundation walls.
2)Be sure you have a proper drainage slope for the grade near the exterior of the foundation walls.
3)Use retaining walls if necessary to keep water from rolling downhill towards your foundation.
4)Use a dehumidifier in the crawl/basement, and feed the accumulated water into the trench that the foundation company is digging.
You can get more info at my website.
Hope this helps,
John Churchill Builder/Instructor at Emory University Author of www.renovation101.com
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Do you need a drain system, is it just humid or is it flooding, did you do everything else, grading, have down spouts not drain nearby, you might need 10 ft extensions. Or is it just humid , something vents and plastic on the ground might cure.
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It pays to cover all other bases before resorting to doing a french drain. We moved into a house in August that had real problems with water in the basement. The previous owner(s) had taken some real half-arsed measures to correct, which probably cost them $10,000 all told.
I graded around the foundation which took care of 95% of the problem. I put a drain box in a low spot in the backyard and piped it to the street which took care of the rest. Gutter covers kept the gutter free of leaves. Total outlay $500. It took a little tweaking with the grading but the basement has stayed bone dry through 3 multiday rains.
Jon
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