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I would like to put a french drain in around three sides of our finished house to keep water away from the foundation and cinder blocks of the crawl space. We get some water in the crawl space after heavy rains. Yes we have slope away from the house.
I will be digging the backfill out to install the drains. The footing is about 3 feet below grade and level (not stepped down) on 1 side and about 50′ wide. The other 2 sides are stepped down.
How deep do you install the drain? It does not seem like a good idea to disturb the soil beside the footing.
Do the holes in the perforated pipe face up, down or sideways?
While I’m at it I would like to waterproof the outside of the cinder block walls. What is the best product and method using common tools?
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Tom
FHB had an excellent article on perimiter drains just a few issues ago. You might want to search it out as a guide.
When we are installing perimiter or footing drains, as they are sometimes called, we lay the bottom edge of the pipe even or just above the bottom edge of the footing. Hole placement will vary with soil types. In sandy or rocky soils we place the holes down or out at about a 45 deg angle pointing away from the footing. If the soil is clay we will place the holes on the top to prevent the silt from getting into the pipe and clogging the holes when dry.
It is common to use 12 inches of 1-1/2" washed round drain rock alongside and above the pipe, so depending on your footing width, you will need to dig about 18" out from the foundation wall. Cover the drain rock with a filter fabric before you backfill so that over time the soils above will not wash down into the rock and clog the drainfield.
As for waterproofing, I would suggest that you check the phone book for a local waterproofing contractor. I don't think it would be worth your time and aggravation to brush or roll on an asphalt "damp-proofing" emulsion for what they will charge you to spray it on.
I would try to determine where your water is coming from first. Ground water can have a tremendous amount of hydraulic force, but it will always follow the path of least resistance. You may not have to step down your drains on the sides if you can intercept the water from the higher level. You may have a high water table in your area and not be able to drain it away effectively.
You didn't mention if the floor of the crawlspace is soil or concrete. If it is just soil, is there a poly vapor barrier down? If the water is only an occasional problem and not across the whole crawlspace, would a small sump and pump be a better solution?
Good luck, I hope I've helped. HV
*Tom:Many people feel that it is best to put the drain i besidethe footing, the thought being to get the water away from the wall/footing intersection, that is so prone to leak. I gather you think it may not be wise to disturb the soil beside the footer at the risk of compromising the foundation base. To better understand this issue, look at this link. Go to the foundation section, and look at the diagram, where it says "no pipes".In reality, if your footers were made by digging a trench and filling the trench with concrete, which is the way they are done here in "clay country", you will be digging in backfill (relatively easy) until you get down to the undisturbed soil next to the footing, at which time your progress will slow significantly. Placing the pipe beside the footer also doesn't work out like in the text book with the stepped footer.HV builds gives some good advice, however I have been taught (and read) that the drain tile holes always go down. What he says about silt clogging the drain makes sense, however the way I combat this is by lining the entire trench, bottom, outboard side, and over gravel, with filter fabric. A few other issues to think about is you need to get your foundation i clean so that the waterproofing can stick. Also, before applying the water proofing, build up a cant strip using mortar at the wall/footer intersection. Also, think of putting some type of drain screen against your new waterproofing job to keep the gravel from puncturing it. 1/2" rigid fiberglass insulation board works good for this if you can find it. Other types of drain screen are available, but they can get pricey. There are pages on the web, which detail the entire process, but I don't have time to search for them right now. Also search the Breaktime archives as this has been discussed several times before. Also also search the Ask the Builder website.One last sugestion: If you are going to do the digging by hand, and you have hard (clay) soil, hire some laborers to help you.
*HV has great advice, and I won't repeat it.There are two types of french drains: (1) One buried a few inches (12-18) below the surface for surface water, such as rain and gutter runoff; and (2) A second buried on top of the footing for seeping ground water.How deep should you bury yours? It depends on what type of water problem you have, surface runoff, or ground water in a low spot. Holes up or down? I used to put them up, so water would flow down into them. My landscape architect claims that they should be down. My soils engineer says they should be up. I'm confused, and I don't think it matters, except if you put them down, add some 10 mil poly at the bottom of the trench to collect the water, and gravel then the ABS.
*One of the excavation companies we use also suggests not putting the drain holes down but at a 45 or up especially in silty soils, however, like sccoter says, facing down seems to only take the water to another spot and dump it out along yur foundation.They also like to put it slightly up on the footing at a high point and then very slightly slope it down to a point where somewher it will actually be below the footing. With rock under as welll as on top. This company also has to dig up lots of old lines and sees lots of older failures, the old clay tile, etc. However recently they have been seeing problems caused by the filter fabric in older set ups that had the fabric wrapped directly on the pipe like the "sock" you can buy. What they have seen in silty areas is the fabric becoming plugged with silt and not allowing the water to get to the pipe. Interesting. So if they are in an area where the inspectors are not picky they will leave it off and not put fabric on untill they are at least a foot above the pipe in rock, and only lay it on top.Then more rock to near level then more fabric and then the dirt backfill. This forms a silt barrier yet water (and some silt) can still get around it and to the pipe. My only visual of it was when someone used it to act as a cap to keep the ends covered and not have "rodents" crawl in ( it came out of a hill side) and it was pluged from the silt being carried through the pipes.Anyone else seeing silt plugging fabric ?
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I would like to put a french drain in around three sides of our finished house to keep water away from the foundation and cinder blocks of the crawl space. We get some water in the crawl space after heavy rains. Yes we have slope away from the house.
I will be digging the backfill out to install the drains. The footing is about 3 feet below grade and level (not stepped down) on 1 side and about 50' wide. The other 2 sides are stepped down.
How deep do you install the drain? It does not seem like a good idea to disturb the soil beside the footing.
Do the holes in the perforated pipe face up, down or sideways?
While I'm at it I would like to waterproof the outside of the cinder block walls. What is the best product and method using common tools?