I just purchase a house built in 1968. I am trying to add a second bathroom on the main level.

Yesterday, I decided to cut some of the existing vent lines (they're galvanized steel) in the home so that I could connect the vent lines from the new bathroom. I noticed that the old vent lines are only 1 1/4" ID pipes (venting bathroom sink and a bathtub/shower). Is this a problem?

I noticed that the old vent lines are only 1 1/4" ID pipes (venting bathroom sink and a bathtub/shower). Is this a problem?
No! Although we run our vents at two inches, One and a half is still acceptable in most areas. Inch and quarter is a little small I don't think that it's worth tearing up your walls to replace it if it's venting OK. Regards, tom

No! Although we run our vents at two inches, One and a half is still acceptable in most areas. inch and quarter is a little small I don't think that it's worth tearing up your walls to replace it if it's venting OK. regards, tom


Thanks Tom!

After looking at some of the plumbing, it looks like some of the drain lines (a bathroom sink, for example) are also 1 1/4-inch.

Also, will I face a problem (with inspectors etc) when I connect a new vent line (1 1/2-inch until the connection) to these older, smaller vent lines?

Have you pulled a permit on the job? Lavatory traps are 1 1/2" reduced down to 1 1/4" with a nylon gasket. It's all going to depend on the inspector.. In our area your vents would be grandfathered in. Good luck, Tom

Have you pulled a permit on the job? Lavatory traps are 1 1/2" reduced down to 1 1/4" with a nylon gasket. It's all going to depend on the inspector.. In our area your vents would be grandfathered in. Good luck, Tom

I'm kind of new to home improvement projects like this, so I am not sure what people mean when they say "pulled a permit". So, I'll give you the long-winded story:

I applied for a permit for room remodeling, which actually requires three separate permits (one each for: electrical, plumbing, and room remodeling). After I pass an electrical inspection (assuming that I do), then I'll have to deal with a "rough-in" plumbing inspection and then a final inspection.

I think that I could get into some trouble when I attempt to connect the vent lines from my new plumbing into the old, smaller waste vents. The main stack is cast iron, so I'm trying to avoid dealing with that as much as possible.

Anyhow, thank you very much for all of your help!

I applied for a permit for room remodeling, which actually requires three separate permits (one each for: electrical, plumbing, and room remodeling). After I pass an electrical inspection (assuming that I do), then I'll have to deal with a "rough-in" plumbing inspection and then a final inspection. That's "pulling a permit".
Call the building department and tell them your concerns and ask their advice.
"Grandfathered in" means that you can keep the old stuff as long vas the new stuff is up to code. Good luck and let me know what happens. Tom