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Lining the bottom of a foundation footing drain with a waterproof membrane

Lining the bottom of a foundation footing drain with a waterproof membrane

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Old 11-19-13, 08:12 PM
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Lining the bottom of a foundation footing drain with a waterproof membrane

Are there any advantages/disadvantages to lining the bottom (and part of the sides) of a foundation footing drain with a waterproof membrane? Has anyone done this?
Traditional design is filter fabric, gravel, then perforated pipe. The way I see it, this results in water filtering through the gravel bed and dissipating in the soil beside and below the footing. The perforated pipe is only there to carry away exceptionally large flows of water that exceed the soil dissipation rate.
By lining the trench with a waterproof membrane and grading the trench ALL the water could be carried away to the sump pump resulting in a foundation footing that is not surrounded by damp/wet soil. This assumes that the water is percolated rainfall; presumably if there is subsurface water then probably not a good idea (or a waste of time) to use a trench liner.
I'm thinking the waterproof liner would need to be perforated at regular intervals to ensure there is no standing water in the liner. (Although proper grading should minimize that risk.)
One disadvantage of a waterproof liner I can think of: if any section tears or develops a leak, then the water dissipation would be concentrated at that section of the footing. On the other hand no liner means water dissipation will always be very spread out.
Comments welcomed.
 
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Old 11-19-13, 09:02 PM
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The design of the drain ( weeper ) system is to only remove the excess water in the soil around a foundation to relieve the hydrostatic pressure. If you remove too much water this would upset the soil conditions and ultimately create problems. I think if you ran that by a geotechnical engineer they would tell you something similar though probably in more detail.
 
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Old 11-20-13, 09:39 AM
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Doing such a thing, especially in the manner you suggested, makes no sense to me. The intent of foundation drain systems is to move as much subsurface water as possible before it can leak into the basement/crawl space, carrying it via a sump system to areas outside of the space one wants to keep dry.

If it were a good idea, don't you think commercial systems would be available on the market, making millions of $$$ for the people who developed them?
 
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Old 11-20-13, 10:56 AM
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Cost

It won't get done commercially (even if it were a good idea) because of cost. The membrane adds to an already expensive project cost particularly if it includes footing excavation and backfill.
My question is whether removing this additional seepage water to the sump pump and keeping the footing slightly drier is of any benefit or whether there are disadvantages (other than cost.)
 
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