foundation drainage specs

[MikeT]

Here's the situation:

On my sloping site, the soils engineers specified that I need to grade the area around the foundation such that soil slopes away from the foundation.  That is easy to do on all sides except on the uphill site.  I need to have the slope regraded to 2H:1V up there but I have an upper limit of a road approximately 25 feet away.   Somewhat complicating the design here is the basement foundation (Modified Victoria's Cottage) is really just an (engineered) straight wall with the main floor kitchen bumpout having a smaller foundation up at that level.  So I need to have that upslope grading be X distance sloping away from the foundation before it heads upslope at that 2H:1V to the road.  So...

What is the minumum I should slope the foundation away from the house before it goes back uphill?  Should I also plan/specify a french drain or some water mitigation system along that "ditch"?

I am so close to being able to submit plans...I just want the engineers' blessing of this plan so I can get their letter of approval and get things moving.  I have attempted to illustrate the section and the situation.

[glenn kangiser]

Our county specifies 5 feet - they use the UBC.  The slope you have is greater than they specify, but that is good as you don't want water standing near your foundation.  You would also do well to slope it center to each side a bit to keep it flowing away from the back of your house.  I don't think a french drain would be necessary if you don't have underground water coming in from the hillside also, however it could be used to get the angle to each side of the house and move water out faster, without sloping the ground to each side.  You would probably want to put a filter cloth over the drain pipe if used to keep silt and debris from sealing it off.  In this case the rolled perforated corrugated drain works well and is economical.

[John Raabe]

The minimum slope is usually 2º which is pretty shallow. More important is that the soil can drain water away since the soil slope will not always be perfect to that accuracy.

I would consider putting in footing drains and backfilling with drainage material so water can get down to this drain. Carry the perforated pipe around the sides and exit downslope to daylight. That will keep any hydrostatic pressure for pushing water into the basement.

A french drain (a seperately trenched drain upslope from the foundation) is more expensive and probably not needed as Glenn mentions.