Foundation Drain

[JohnnyB_]

Hello -

I am designing a garage with an ADU above. The soils are a moderately expansive clay requiring a 2 - 3 overex. Groundwater has been encountered at approximately 3-4 feet below grade. Due to this I am designing the foundation as a mono pour slab with a turndown. The turndown will extend 24 inches below grade. The grade around the 1/4 acre property does not have enough fall to facilitate surface water away from the foundation using a standard drain pipe and gravel perimeter drain.

Is a perimeter foundation drain warranted? I can't figure how it would be beneficial in this particular situation.

Thanks in advance.

 

[CarlB]

If there is no outlet for the subdrain pipe, such as to daylight, ditch, storm drain, then the subdrain & pipe would serve no purpose.
But you could run it to a structure/vault, such that if water did rise above the drains, a sump pump could be dropped in it and water pumped onto the ground, away from the building. This could lower the groundwater level below the building, which may be of some benefit.

 

[JAE]

Foundation drains are typically used for basement wall conditions where you are trying to minimize lateral soil pressure against the wall. Not appropriate in your condition in my opinion.

 

[JohnnyB_]

Thanks for the replies.

 

[HTURKAK]

I would prefer grading with if necessary engineered fill and provide slope to facilitate surface water away from the ADU found.Perimeter foundation drain will not be warranted in your case ..





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