Leaking Crawlspace


Old 03-25-06, 11:01 PM
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Arrow Leaking Crawlspace

Hello. This is my first time here so if there are rules on length of posts that I don't know about....sorry for the long post.

My house is situated on a rectangular lot (urban environment) which is part of a hillside that slopes towards the back of the house. I have a french drain installed that is parallel to the back of the house, but I am still getting groundwater coming into the crawlspace during heavy rains. The situation is not helped by the fact that my foundations are in marginal condition (there are settlement cracks in the concrete up to Ĺ in. thick due to expansive clays and effluoresence in the concrete). Another complication may be the way the ground slopes. The low spot is at one corner of the house (NE corner), while there is a high(er) spot at the other corner of the house (NW corner) and at 90 degrees from the NE corner. In other words, the house is at about a 45-degree angle to the steepest slope. I should also mention that the house has a daylight basement along the back side of the house. There are concrete steps from this basement down into the crawlspace, which has a concrete slab at the bottom of the stairs and the three spread footings for the house. The middle footing has a pretty big vertical crack in it that water is visibly seeping through even though this crack is located about 15 feet from the back of the house. I donít know how deep the footings are along the back side of the house. I should also mention that the amount of water coming in is minimal. The worse case has been Ĺ inch.

My thoughts and questions on this are the following:
1. Do I have the French drain in the wrong place (horizontally and/or vertically)?
2. Will waterproofing from the outside do anything for me? It appears that groundwater is somehow getting below the upper footing and down to the lower area. Will waterproofing the upper footing do anything for me? Do I need to replace my cracking foundations? Do I need to make the upper foundation go as deep as the deepest footings?
3. Will a well or a sump do anything for me?

Any suggestions/thoughts would be appreciated. Thanks for reading.
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Old 03-26-06, 12:41 PM
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curtain or "french" drains

I don't think that this is the right forum for this problem, but I will answer anyway.
Picture ground water filling all of the voids in the rock and dirt below grade. When you get a lot of rain, that water level rises. The normal water level is hopefully below the level of the bottom of your foundation, but may not be. It is certainly higher than your foundation when you get a lot of rain. A foundation drain, curtain or "french" drain uses the principle that water flow seeks the path of least resistance.

A properly installed foundation drainage system consists of perforated pipe (not cheap stuff, like "elephant trunk" that collapses easily; installed with the holes [I]down[I]) that is installed in a bed of crushed stone, at or below the level of the footer. The pipe should be covered with several inches of crushed stone and then with a layer of something (hay works well) that will kepp the dirt from clogging up the stone and pipe. The trench must then be backfilled with clean sand or gravel, which will allow water to drain easily down through it. The pipe should be continuous around the entire foundation, with a tee off to daylight somewhere. If it can't go to daylight somewhere lower than the drainage, you can't get rid of the water.

A curtain drain is more specifically a trench across an area to keep water away from that area. It may be a trench alongside the uphill side of a driveway or a leach field. Water can still get under the bottom of a curtain drain, so it must be deep enough for the given purpose. Your curtain drain may not be installed deep enough, far enough across, with proper materials, or with a drain to daylight.

I am confused as to the structure of the foundation, since you refer to cracks in the concrete foundation, but also speak of footers (plural). I don't think that a sump pump is going to help anything. You will still have wet expansive soils outside the foundation that will freeze and expand.
The footers below the foundation walls should be below the frost line. You don't say where you live.
Waterproofing will do nothing for you. Coatings on the outside of the foundation are actually damp proofing. Water under pressure can usually still get through.
I hope this helps.
Old 03-26-06, 03:24 PM
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Response to Fixitron

Fixitron, thank you so much for your response. Based on your description, I think the french drain was installed properly and with the right materials. It wraps around the foundation and dumps onto the sidewalk. I tested it this morning. It sounds like it's not installed deep enough.

The house foundation is mainly 3 concrete grade beams that run down the length of the house. The back of the house is on the (skewed) upslope and the front of the house is on the (skewed) downslope. The back of the house is a half-daylight basement (i.e., "upper" basement). So the foundation that runs along the back of the house is a cantilever retaining wall type foundation with a slab on grade concrete floor. Two of the grade beams are exposed in the basement, the other one covered with a plaster wall. The crawlspace also has a concrete slab on grade floor for a few square feet (the crawl space has enough head room to be used as living space), and I think (but I'm not sure) that the concrete stairs that lead down to the crawlspace retains the soil that is below the (upper) basement concrete slab. I guess I have a terraced foundation if such a thing exists. Sounds like I need to bring the french drain to the level of the lowest foundation level. I live in the Bay Area, California so there is no freeze/thaw-only wet/dry.
Old 03-26-06, 04:28 PM
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Fixitron provided you with an excellent analysis. I might add to his idea of providing a 4" continuous drain tile in washed stone with this suggestion: On the uphill side of the house you might have to consider digging out the backfill to the foundation. Line the sides of the new excavation with geo textile cloth and backfill with wash stone from footing tile to grade. Waterproof the exposed wall as best you can before dumping in stone.

I believe your foundation may be suffering from hydrostatic water pressure. Over time, this pressure from water can push a basement wall in, especially in a walkout basement. By installing the wash stone backfill, Water has not nearly the opportunity to provide pressure against a basement wall. Instead of water building up and pushing hydraulically against the uphill wall you have provided a path of least resistance. The water drains down swiftly to the drain pipe at footing level and continues it's escape to the daylight outlet that fixitron speaks of.

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