Two designs of a new washroom for review

[Buttonsrtoys]

I'm adding a half-bath to on the first floor and tying into an existing sanitary line for the full bath above. Below are two designs. Design "A" runs the vent for the half-bath above the flood level of the fixtures in the full bath. Design "B" is a bit simpler on paper, but the existing riser is in an exterior wall next to a post at the point of the tie-in, so its a bit trickier to build than design "A". The sketches don't show the jogs in plan-view, which some lengths I relate may look out of scale.

I annotated the sketches with ABS pipe sizes and lengths. Blue lines are the existing sanitary, green is the new.

Are both of these designs OK? Code-wise, I'm in Nova Scotia.

[hj]

Desigh "A" is the only one that will work and that assumes you actually install it the way it is drawn. "B" would not pass any code that I am aware of.

[Buttonsrtoys]

Desigh "A" is the only one that will work and that assumes you actually install it the way it is drawn. "B" would not pass any code that I am aware of.

Thanks hj. I'll install "A" as drawn. What's wrong with "B"?

[cacher_chick]

"B" is not acceptable because once the line has been used for a drain, it can no longer be used as a vent. The only exception is the wet vent of the water closet past the lavatory.

[kreemoweet]

"B" is the old "single stack" plumbing system design, as far as I know it was outlawed in the early part of the last century.
Also, in "A", I think you need to keep the toilet/lav vent size at 2 inches all the way up, rather than reducing down to 1 1/2
inch as shown.

[Terry]

A

And like mentioned above, keep the lav, including the vent, 2" all the way up to the next floor on the revent.
You can use the 1.5" traparm for the p-trap on the lav.

Below is an example of wet venting

[Buttonsrtoys]

Thanks guys. "A" it is with a 2" vent. Wet venting makes my head spin...

[hj]

quote; Wet venting makes my head spin

Wet venting is simple, but your ""B" is an illegal "wet vent" because you cannot wet vent between floors.

[Buttonsrtoys]

quote; Wet venting makes my head spin

Wet venting is simple, but your ""B" is an illegal "wet vent" because you cannot wet vent between floors.

Ah. That clarifies what was confusing me. So wet vents are OK provided their short/restricted to the same floor. Thanks! Now I'm curious - why are long wet vents between floors a problem?

[Terry]

why are long wet vents between floors a problem?

The same reason that standpipes can only be so long. They siphon traps.