Two designs of a new washroom for review

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.

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.

hj said:

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.

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

"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.

"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.

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

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

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.

hj said:

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.

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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?

why are long wet vents between floors a problem?

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