I have received different advice from contractors about the correct way to install a french drain. Some have stated the drain needs to be installed below the foundation line and at least 4 ft away from the house. Others have stated that they only need to dig a 12 inch trench right along the foundation. The area I live has a hight water table and the area under my home becomes wet each winter.
What is the correct answer?
Re: French Drain
French drains are actually placed along the footing portion of the foundation; the footing is the steel-reinforced wide protuberance at the base of the wall that is poured first, allowed to cure, then the foundation itself is poured on top of that; the Popular Mechanics site below indicates the placement (labeled "drain tile").
Since the footing & foundation wall are poured separately, there is a seam between the two that could allow water into the basement if the french drain is positioned too high.
It is also important to note that this is a gravity drain system; thus, the drain pipe leading away from the foundation to an outfall or drywell 20' away, must be pitched down so the collected water flows away from the foundation.
The lower foundation wall & footing are painted or smeared with a waterproof tar product to seal the wall.
The french drain is covered with crushed rock & landscape fabric is installed to prevent fine soil particles from clogging the drain.
The PM site also emphasizes the importance of getting the roof gutters in good working order & diverting this water away from the foundation with extensions on the downspouts; also, the ground near the foundation has to be pitched away from the house.
The 2nd site makes the point that some "french drains", especially in Europe, use just crushed stone & gravel ("soakaway") without installing a drain tile (perforated sewer pipe)
Re: French Drain
Pay close attention,as jacktheshack stated to the position you place the drain.I had a professtional company(or so i thought)come in and do my house.They missed the water table and placed the drain too high.They have to redig my basement and accually made the problem worse.