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Old 10-15-2009, 05:17 PM   #1
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French drains


Debate among fellow builders. french drains in a crawl space, some are saying to put in directly after block work without grading the inside of the crawl. I believe that you should create a direction on flow to the lowest point of the crawl. Also one says that the drain should run completely around the crawl instead of on the wall where the water would collect. Some say to put the drain on the outside of the crawl if there is a good amount of fill dirt say on the front side of the house. your thoughts, always good to get a few opinions.

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Old 10-15-2009, 05:26 PM   #2
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For the vast majority of my projects, I design the perimeter drain to run around the entire building on the outside of the foundation, or if it is a spread footing with wall, I sometimes run the perforated pipe on top of the footer. The key is to make sure the perforated pipe is at least six inches, preferably a foot lower, than the floor of the building. Of course, the pipe has to drain to a low point that is dry, I can't tell you how many drains I have seen that "drain" to a spot that is below the high groundwater table, therefore the groundwater runs into the "drain" and floods the building when the water table rises.

The pitch of the drain is not too important, I like at least 1 percent, but the drains still work fine even if they are dead flat, as long as they are correctly sized and installed. I always specify wrapping the pipe with filter fabric, and the pipes need to be placed in a crushed stone trench, typically at least 2 or 3 times the width of the pipe (18 inch trench for a 6 inch pipe is pretty typical).

The only time I have been involved in interior drains is for repair work to fix a problem, i.e. there was no perimeter drain and now the client has a problem. On really large buildings, I have also specified one or more cross pipes under the floor, connected to the perimeter drain on both sides. Not really necessary, but it adds some redundancy to the system, which never hurts. For the average house, totally unnecessary to have cross pipes, a perimeter drain with 4 inch perf PVC is generally adequate.

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Old 10-16-2009, 07:17 PM   #3
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if you ask me, forget doing anything we get paid VERY well to fix bldrs' f/u's amazed the bldg code still allows .003 asphalt emulsion for dampproofing barrier,,, another bow & atta-boy to the waterproofing gawds ! ! !
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Old 10-16-2009, 08:55 PM   #4
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French drains


http://www.servicemagic.com/article....age.13702.html
For later cleaning: http://www.easydigging.com/Drainage/pipe_tile.html
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Old 10-16-2009, 08:58 PM   #5
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Quote:
Originally Posted by itsreallyconc View Post
...amazed the bldg code still allows .003 asphalt emulsion for dampproofing barrier
True, but remember that meeting code is basically the equivalent to getting a D in school...Passing, but the work sure isn't as good as it could be.
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Old 10-17-2009, 04:37 AM   #6
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D-, 'mite,,, if anyone's interested, there's more inf on my website,,, no financial interest as we wouldn't accept work from anyone thru the list forums

our systems are AT footer level thereby avoiding ' scour ' problems,,, we ALWAYS line the trench w/filter then add some bedding 3/4"- rock,,, we NEVER use the pro-filter'd pipe preferring to keep silt far away from the pipe,,, 4" perf ads probably as dan,,, stone on top & fold back the fiver the trench,,, we also, if needed, make conc/masonary repairs as rqd,,, if its a wall leaking, we'll coat w/sonneborn sonolastic & pvc miradrain protection layer,,, backfilling consists of building a crush'd stone column next to the pvc & foot-compact'd soil.

we have always felt it better to manage the wtr AT footer btm elevation for backfill-leakage problems - below that for rising water-table,,, sometimes the tricky part's figuring out IF its genuine wtr table ( moonachie/secaucus/belmar ) OR the false wtr table usually found in residential,,, ask me about the 3.5MGal tank we waterproof'd in moonachie where the bay was actually hudson river/estuary

we've installed residential laterals IF it seem'd necessary - 2 pumps over 100lf & wtr-power'd backup pump,,, battery-power'd pumps are better'n a sharp stick in the eye but not much

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