Alexander Galkin wrote:

I recently gave a thorough look at me 50+ years old house plumbing as I am
going to build a bathroom in the basement and I need to change it. What I
found is that my kitchen sink, lavatory on first floor bathroom, washing
mashing in basement and utility sink in basement do not seem to be vented.
They all drain in main 3" drain stack. All second floor bathroom fixtures
also drain in the same stack. I believe the main stack eventually goes
through the roof as a vent. As far as I understand all fixtures vents must
connect to main stack above all drains so I came to conclusion that first
floor bathroom fixtures and basement fixtures (washing machine and utility
sink) are not vented properly. Can this really be in 50+ house or my house
as an unpleasant exception? I live in central NJ. I actually have a 2" vent
that goes from basement but only first floor toilet uses it. Can I use this
vent to vent other fixtures too or the vent size is too small?

The 2" vent should be fine to vent the additional fixtures.

The 3" drain may be too small to add an additional toilet
(technicality).

If you *really* want to know the limitations, you'd have to ask the
town inspector.

Jim