Replace S-trap with P-trap or chicago loop?

All fixtures in 1920's 2nd floor bath are stack-vented. Sink curently uses S-trap to floor with about a 7-foot run to stack.

We would like to improve this situation without adding a new vent up though the roof or reventing back to the stack through a wall, which would entail ripping apart the plaster/lathe walls and disturbing the ancient soil stack.

What about a "chicago loop" type thing like people do in kitchen islands, where the new sink's P-trap goes back into the wall and then includes a loop in the wall, as shown, where the top elbow is higher than the water level, and where the drain line back to the stack in increased to 2".


Would this work? Any other ideas? Our town uses the International Plumbing Code rules.

With an accessible C/O added to the vent side of the loop and the DWV piped in 2" it will work fine.

I've never made the loop but here's the way I've seen it done.... popular in some of the luxury homes nearby...using all 2" PVC drain lines.
http://i149.photobucket.com/albums/s...CAL/sink-1.jpg

If you check the drawing for an approved loop, you will see it requires a vent off the side of the loop's vent to a wall and then up to a termination. However, since it would be hard to fill a 2" pipe with a lavatory drain, there should be enough room for both air and water to co-exist in that configuration. When I have used the configuration shown, I had to use 3" for the lateral line to ensure that there was always an air passage available.

Thanks so much for your replies and advice. This has been extremely helpful! We are planning to do as advised above, in the wall behind the sink.

We did the demo over the weekend and found a rats nest of old plumbing under the floor. Apparently the house was originally plumbed with lead cold water lines, which were changed to copper at some point. All the old drains were still lead: so funny looking! As we've had problems with these old lead drains leaking and wrecking the kitchen ceiling below, we are happy to be replacing them with new pvc!

Stacey