Double Lavatory drain/vent question

I'm planing on installing a new, double lavatory, vanity in my master bathroom. Current bathroom has one lavatory and is located on the third floor of my condo Bldg. Wondering if I should attach to the existing wet vent with a double wye fitting or two individual san tees? With the cathedral ceiling, the top of the existing vent (on the roof) is approx. 15' above the center of the lavatory trap arm.

Curious on how I can properly support the upper, steel, portions of the vent -once the lower portion is cut out to accommodate the new, ABS, fittings? Any advice is appreciated.

Thanks a lot

Robert
in California

This image, from a previous thread, really helped me out.

Thanks Terry!

Any reccomendations on best way to connect new ABS, 2", double Wye fitting to existing, steel wet vent? ie....flexible coupler, vent supports, etc.

My existing vent stack/plumbing was built in 1970.

A coupling with a stainless band, or shield around it to keep the pipes from shifting.

The above picture would not be legal where I am, as the use of the double combo (double wye 1/8 bend) is a fitting which does not allow for adequate venting of the traps. The vent inlet will be below the weir of the trap.

An adequate alternative would be a sanitary cross with a clean-out tee above, or stacking two san tee's, wet-venting one of the lavs.

If a double combo were used as above, vents on each dirty arm would be required.

What is a double wye fitting that is equivalent to two, back to back, san tees called? Is it.....double wye 1/4 bend or back to back fitting or ????

I ask after looking at the, earlier, mentioned picture that appears (in my novice world) to have this type of fitting and not a double combo? Please let me know what I'm missing. Thanks






This one uses 2" which also vents the toilet.

fitting

That is not a double combination Y-1/8 bend, it is a double fixture cross, which is an approved, and actually the only approved, fitting for back to back installations. A sanitary cross is not approved because the two openinngs are across from each other with no barrier to prevent cross splashing.

Codes are a bit different where I'm from.

The 'barrier to prevent cross-splashing' is viewed as destructive to trap protection here. "Vent opening shall not be lower than the weir of the trap."

I stand by my diagrams above, for my area of the world.


https://terrylove.com/forums/attachment.php?attachmentid=707
https://terrylove.com/forums/attachment.php?attachmentid=708