I am installing a french drain along the foundation of a residence. I have always place thick plastic sheeting (6mil) up against the trench on the foundation side and on the bottom of the trench. Afterwards I lay 2" of gravel,fabric,pipe,etc. Is it over kill to do this? My reasoning is that it helps force the water away from the house and into the pipe.
Oh heck no. I go deeper than that myself and typically apply a rubber or asphault-base coating on all the masonry, then put poly over that.
Nobody, anywhere, ever said "this crawlspace is too dry".