Rough in plumbing under slab

[Rick Johnson]

I am having a detached garage built with plumbing and a 5' thick floor. On Friday my concrete contractor set the foundation wall forms (this is not a monlithic pour). I am concerned that the sleeve for the sewer line is too high. The top of the sewer pipe will be 17" below the floor grade as it goes through the foundation wall. The sewer line must go 40' farther in order to pick up the toilet and a floor drain. That will put the top of the pipe about 7" below floor grade using the 1/4" of fall per 12" of run. Is 7" below floor grade enough to accomodate the traps and vent? There is enough fall beyond the wall that would allow dropping the sewer line 6" more under the floor.

[roger g]

Also,is seventeen inches below the frost line. I hope in that 40 feet you are not going under a driveway where as you know the frost line goes much deeper.. I would check with a plumber to make you feel better. Different standards for different areas.


roger

[Rick Johnson]

Good point Roger, the 40' is under a radiant heated slab, after it leaves the foundation it goes much deeper.

[scwoodcraft]

Forgive a possibly foolish question but why worry about frost hurting a drain line. If the line is properly sloped, shouldn't it be empty and thus uncaring of whether the surrounding ground is frozen?

I ask because I'm about to start trenching for the very same thing.

[Rick Johnson]

Forgive a possibly foolish question but why worry about frost hurting a drain line. If the line is properly sloped, shouldn't it be empty and thus uncaring of whether the surrounding ground is frozen?

I ask because I'm about to start trenching for the very same thing.You are probably correct. I talked to my plumber before the wall was poured and he did not have a problem with the height. He has since completed the undergroud work and the floor has been placed.

[Tom R]

Forgive a possibly foolish question but why worry about frost hurting a drain line. If the line is properly sloped, shouldn't it be empty and thus uncaring of whether the surrounding ground is frozen?

I ask because I'm about to start trenching for the very same thing.

I could be wrong, but I would think frost 'could' hurt the drain line by causing a 'heaving' action which could either crack the line, or not 'settle' back enough to keep it's proper slope.

[roger g]

Drain lines do freeze big time. Not all the water runs away before it freezes and over a period of time this freezing of little streams of water will eventually build up and really plug your drain. I'm talking of really cold temperatures. On really cold nights in Canada you can get main water supply lines freeze (I'm talking city lines! 10 inches in diameter) freeze solid and burst. And this is running water!!!! Plugging a drain line is a piece of cake to Jack Frost. Just be aware.


roger