A friend is having a shower installed in a second floor bathroom, directly over a stairway landing. The floor joists are only 4" deep, such that a trap under the shower would protrude into the head space in the stairwell. The plumber gave two options: raise the shower floor four inches, such that people using the shower would have to step up roughly 8 inches into a high shower floor, or to offset the trap for the shower drain about 18 inches away, in an area where the floor joists run 10 inches deep. He said that a building inspector told him he would okay the offset trap, but I've never seen it & my friend is afraid the plumbing won't pass inspection. So the question: is a trap ever okay set away from the drain opening of a fixture?

If I understand your situation you are wanting to leave the shower drain where it is and move the trap to a location some 18 inches away. This is called a running trap and are use is some places. I think what the inspector would be interested in is the total distance from the drain in the bottom of the shower to the pipe in the wall that it would drain into including the length of the trap. The best things to do is to talk to the inspector and tell him your situation and see what he says.

Thanks so much for your fast reply!

Once more letmetellu steped up to the plate and hit a home run. If you can get it passed a running trap,(see image) is the answer. Regards, tom

Thanks, Speedball1 and letmetellu -- the trap would be roughly 18 inches from the shower drain, and beyond that, another roughly 5 feet to empty into the cast iron waste pipe. The concern would be any pressure or siphoning in the line that might empty the trap, of course causing an expensive renovation to be unusable.

Will this be permitted and inspected? At 5" with a 2" trap and drain line you will fall within code if the running trap passes. Good luck, Tom