Good evening/weekend all,
I'm doing some remodeling that requires moving the drain line for a shower. There is almost no good way to do this, so what I'd like to do is kill 2 birds with one drain line and put it into a new furring wall on an exterior double brick wall, and then spray the furring space with spray foam. This way I can route my new pipe to the stack, and get some insulation value in the cold wall of the bathroom below it at the same time.
The question is, can I run a 2" drain line with the fittings literally touching the brick of a double withe exterior brick wall without concern of freezing? I'm in Pittsburgh, PA, we get fairly cold winters here. I'll spray foam all the way around the pipe, but the side of the drain line will be essentially touching the brick and therefore not really protected by the foam. I have 3" absolute max to fur out, or I'll encroach within 15" off this wall to toilet flange, so there's no room to hold the drain off the wall. I plan to attach 2x3 (2 1/2" actual depth) studs to the brick and leave a channel for the drain line. With the variations in the brick surface, I should be able to just squeeze the fittings into that much space. I have enough vertical room that I can put a decent amount of fall in (an inch/foot shouldn't be a problem), to make sure that water moves through this section of pipe quickly and has no chance of water resting in the pipe. The run against the wall would be about 6-7 feet long, then drop into the 3" stack.
The vent is fine in its current location, so not worried about it.
Related to this, I'm assuming that I should use a 2" drain, as the shower has 2 shower heads... is this correct, or would 1.5" be sufficient? Last thing I want is any chance of a slow draining stand up shower, but the extra 1/2" would be helpful if the 2" pipe is not necessary...
Thanks for your help guys!