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I need to add some foundation drains to my house to eliminate the damp crawlspace. I read several discussions on this subject, some of them referring to FHB issue 95. I was going to order that issue, but the article is described as “Moisture-Proofing Systems for New Basements”, which is not what I’m doing. Can someone do me a huge favor and dig up issue 95, and tell me if it in fact addresses retrofit applications for French drains, other drainage types, etc, or is just for new basements? Thanks in advance.
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Leon: FHB 95 article in question pertains to basements, new construction, although you could adapt these systems for retrofit as necessary. Your situation, however concerns a crawl space, which is by definition,
i above grade.
At least a crawl space should be above grade...dampness in crawl spaces is usually the result of :
a) poor site drainage
b) inadequate venting
c) comb. of both
Most damp crawl spaces I've seen have the foundation vents placed incorrectly allowing moisture to accumulate in the corners of foundation walls, proper vent design allows good "cross flow" and avoids "dead zones", areas where there is inadequate air circulation. Following a formula for req'd vent area/square footage or lineal feet of wall are not sufficient without addressing where the vents are placed and how air will circulate in the crawl space. Common sense can show you where logical vent locations will provide the best ventilation. As a last resort, I have seen forced air circulation systems installed with good results.
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#95, pp48 is titled "Selecting a Moisture-Proofing System for NEW Basements. Nothing about French Drains - just the sticky stuff for foundation walls.
scc
*see Journal Light Construction web page "techniques"( jlcon )lots of discussion on this. 3) problems:migration of moisture from earth. or #2) high water table or #3 condensation of moist air on contact with cool surfaces. Usually, combination of 1 & 3, but sometimes all 3 conditions exist at different times of the year. Do you know the source or is it the combo? Let me know & I'll give u my 2 cents when I'm at some other machine. This one is connected at 9600 and I'm out of here.
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Guys, thanks for your responses! It looks like I don't need to get issue 95 as it doesn't address my problem. Perhaps you can help me find a solution. Here's the setup: The house is on a hillside property, which slopes from front to back, about 1 foot drop for every 4 feet horizontal. As you stand at the front (high ground), the front stem wall is about 60 feet wide, and its top is just above grade (so there are no crawlspace vents along the front). There is another stemwall about 20 feet back of the front. Because of the hill, the back stemwall is about 5 feet lower than the front stemwall. The area between the front and rear stemwalls is the crawlspace. The area behind the rear stemwall is a full above-grade basement, so there are no vents along the back stemwall. Thus, the crawlspace is only vented on the two side walls, which are 60 feet apart (which is probably inadequate). The front yard is about 40 feet wide lawn and 20 feet wide driveway. The crawlspace is damp only in the area behind the lawn, and is dry as a desert behind the driveway. This suggests to me that the dampness is caused by water going into the lawn (from sprinklers and rain) and then working its way through and under the front stemwall into the crawlspace. As I mentioned in a previous post, this has caused some stemwall cracking. I've had fans running in the crawlspace for the last two weeks, and it has made a definite improvement. However, I would like to control the flow of moisture into the crawlspace by incorporating a drain along the front stemwall (gives me a good excuse to put in a new paver stone driveway!). What I'm trying to get smart on is what kind of drain should I use and how deep should I place it? A french drain in gravel? One of these new multi-tube drains that only require a narrow trench? Also, because of the hill, how deep should the drain in front of the house be to make sure the water doesn't come up ahead of the rear stemwall which is about 5 feet below the front stemwall? The soil is expansive clay, and I have no clue as to how subsoil drainage works in this soil. Does the water tend to run straight down, at a 45 degree angle, or closer to horizontal? Any suggestions would be appreciated!
*If you have an expansive clay soil, drainage will be poor. You first have to determine the gradient your drainage is following..you seem to already have a good idea of thie direction. Then your strategy should be to intercept the flow before it saturates the soil beneath your crawlspace. I would contact the Mirafi company..they probably have a web site. They make geotextiles and drainage fabrics...what you want to construct is a filtered drain, probably using 4" dia. perf. pipe, slots down, on a min. 1/4"/ft grade, wrapped in an envelope of drainage stone and filter fabric, the Mirafi product. Run this drain as a perimeter french drain and daylight it out in an obvious location.
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1. excavate down about 16". Line the trench with at least 10 mil plastic.
2. Add 2-3" of 1" rock.
3. Run 4" solid perforated ABS in trench next. There is a big debate on whether to have the holes up or down. My friend the landscape architect claims holes up; I say holes down. Slope the ABS 1/4" about every 2 feet. This shouldn't be a problem on your site. Cover the ABS with landscape fabric, usually in 3' wide rolls.
4. Run the ABS to the rear of your property and either into a homemade cistern or out the back into your neighbors yard, and let him worry about it. The home made cistern is just 3 50 gal drums with holes drilled into them, and filled with 1" rock. Cover the cistern with landscape fabric as well.
5. Cover the crawl space with 10 mil plastic and overlap the seams by 1' or so. Weight it down with some sand or pea gravel in selected places.
Jeez, if that doesn't work, and it is still wet, I'd run two ABS lines, one high (16") and one low (48") and have a pre-cast cistern installed.
Good Luck!!
*Leon,
Joseph FuscoView Image"Whenever, therefore, people are deceived and form opinions wide of the truth, it is clear that the error has slid into their minds through the medium of certain resemblance's to that truth." Socrates
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I need to add some foundation drains to my house to eliminate the damp crawlspace. I read several discussions on this subject, some of them referring to FHB issue 95. I was going to order that issue, but the article is described as "Moisture-Proofing Systems for New Basements", which is not what I'm doing. Can someone do me a huge favor and dig up issue 95, and tell me if it in fact addresses retrofit applications for French drains, other drainage types, etc, or is just for new basements? Thanks in advance.