Is the following S Trap setup code compliant?

Original 1932 Crane Pedestal sink. Vertical S Trap from sink drain into floor. Four inch stack/vent about 3.5 feet from sink. No additional sink venting. No problems with sink draining (water drains normal).

The reason why I ask is the bathroom is under a rehab. It is impossible to install additional sink venting in the wall. The bathroom was originally built 80 years ago, all wall 2x4’s where turned sideways to allow maximum floor space. Inner wall cavity space is less than 2 inches. Since the walls are plaster, the plaster keys consume much of the inner wall space. Running any vent pipes internal to the walls is impossible. The walls offer no structural support but I can not bump out or in ANY walls.

Obviously, the only sink venting is from the main four inch stack 3.5 feet away. Tied into the four inch stack is the toilet (1 foot from stack) and tub (five feet from four inch stack). I have a similar venting situation with the tub too.

Any advice is appreciated. - thanks

What kind of advice do you want. The "S" trap is illegal under every code. Your sink drain will work "good" under most conditions, in fact it may work better than if it were vented, which is the problem, since it will also "suck" the water out of the trap almost every time the sink drains. You have to either find a way to vent it, or live with what you have. Sounds like a Frank Lloyd Wright house, that was his manta also, "make every inch count", although his also had narrow corridors and stairways, with low ceilings.

HJ - Believe it or not, two years ago a licensed plumber installed an S trap in our totally remodeled kitchen for the kitchen sink (not an island sink). It is NOT vented. The licensed plumber ran 2" PVC to the main 4" pipe (about 6 feet away). A permit was pulled and passed rough and final inspected. *How the heck did this get by the inspector?*

I'm not debating your response since I heard the same about S traps and that is why I an posting here. In the bathroom situation, an S trap setup can't be avoided w/o serious wall modification. The previous bathroom sink setup used an S trap and we never had any problems with the trap being sucked dry. The sink trap is 1.25" and goes into 2" pipe at the floor level.

If I'm lucky, I may be able to shim out the bathroom wall on the sink side. If so, I may be able to rum PVC for venting, however it will be considerbly smaller than 2". I may be able to run a 1.25" vertical vent pipe. My question is **What is the smallest diameter vent pipe can I run for venting the bathroom sink if the drain pipe under the floor is 2" PVC and be code compliant?

Many plumbing codes permit the repair or replacement of fixtures or piping configurations that do not meet today's plumbing codes as long as there are no major Health of Safety issues. Replacing "S" traps is o.k. as long as it is not a eminent health matter.

The only time that our state plumbing code mandates change is when someones health and/or saftey are a concern such as installing a new T&P valve on a new water heater and not using the old pressure only relief valve or ordering new water piping for rental propety when the water pressure and volume are so low that the 2nd floor toilets can not fill for there next flush when the first floor kitchen sink is running.

in order to be code compliant, the drain must have a P trap going towards the wall not an S trap going thru the floor. if you are using a vanity, you can put the TY at the back of the vanity and put a street 45 in the top of it aiming into the wall. mass code says the vent must be 1/2 the size of the pipe it is venting with a minimum size of 1 1/4". so you can reduce the vent to 1 1/4" at that point and run it to the attic or thru the roof. it has to be increased before going thru the roof. around here 2" is the minimum size thru the roof, other codes want it to be larger.

I would cut a tee into the main stack, and point the 1-1/2" outlet, down the wall to the C/L of the lav. If you are within 4 ft of the main stack, you will have no problems w/sidearm distance. Put a 90-deg turn-out of the wall, and put a thread adapter on. When you finish the wall everything will be legal and have a new drain.
Good Luck,

Rudy

One problem with that is by the time he cuts out the "flat" 2x4's for the pipe, the wall will lose all its strength and rigidity.

How about a 1-1/2" copper DWV drain w/ an 1-1/4" vent? If the tee's low, it shouldn't have much impact on the wall. I've never run a vent that small but have read in the codebook where it's allowed.

A 2x4 flat is only 1 1/2" thick so any drain line through it would cut it out entirely. You might get by with essentially removing one stud, (the lath would help support it above and below the cut, but any more than that and the wall might collapse if someone fell against it.