Hi, We are preparing for an upstairs bath renovation in a 1 ½ story timber-frame house. Each floor will have 1 full bath with the kitchen also on the first floor & the washer in the basement. The house was owner-built in the 80’s & there are a few un-vented fixtures & I would like to correct any faults during the renovation process.
My question is regarding venting. It is not clear to me if is it required to maintain a constant stack all the way from the sewer to the roof (3” in this case) or can I treat the two floors separately (10 fixture units 1st floor, 6 fixture units 2nd floor) venting each floor with 2”, then joining the two into a 3” vent in the attic for the roof penetration ? The timber frame of the house makes pipe runs even more difficult so the smaller diameter would make things quite a bit easier & minimize any boxing in that is likely to come up.