Purpose of Residential Basement Floor

[mas]

I plan on installing an interior French drain around the perimeter of my full depth basement and was warned by a contractor that the basement floor should not be entirely cut (or separated) from the basement walls (via the French drain trenching and subsequent slot) because the concrete floor acts as a beam and keeps the bottom of the basement walls from kicking in, much like floor joists.

I'm skeptical of his explanation.

Any truth to his claim?

 

[cobadger]

Yes and no. It depends on which side of the basement wall you want to put the French drain. The basement floor slab acts the same was as the floor joists and does indeed keep the bottom of the basement walls from kicking in. The basement wall is designed as a beam tilted on its side with the floor slab and wood subfloor acting as the reaction points. The drain usually goes on the outside of the basement wall to move any water that seeps down the wall away from the house. The basement slab is typically poured flush with the inside of the basement walls.

Hope that helps.

 

[eric1037]

Why would you have slots in the slab? Am I missing something? It seems that if you have high groundwater that you are trying to deal with you could just have perforated pipe below the slab and have it all go to a sump to be pumped out.

 

[mas]

The house is existing - about 80 years old.
I'm getting water in the basement, mostly through the walls.
The French drain (perforated pipe surround by crushed stone, enclosed with filter fabric) will be installed on the interior perimeter.
In order to install a French drain, I'll have to trench it, thereby penetrating the slab.
In order for water to drain to the French drain, typically a 1/4 to 1/2 inch gap is left open between the wall and the concrete patch atop the trench. This permits the water to drain down off the wall and into the French drain - never making it out onto the basement floor.

An exterior perimeter drain would be much more costly than an interior drain.

 

[haynewp]

It could kick the wall in making your drain not work so well. I commend the contractor for thinking that way.