No vent Or looped vent

I am doing a bathroom remodel. I am moving the sink to the opposite wall, which will now be next to the toilet. If I run a 2" drain (instead of 1 1/2") do I need to vent it since the p-trap will be 26'' to were it ties into the main stack ? It will drain in below the toilet. Ok I think I'm reaching.

If that won't work, can I loop a vent and go back to the original wall to pick up the old vent? the other wall is 6' away but I can keep the horizontal section above the drain line.

If it weren't for the lath and plaster I would just go up and tie into the vent.

Thanks for any help

It'll depend on the code in your area, and if there is a bathroom above using that stack as a drain. Is that what you mean by "it will drain in below the toilet"? In my area, if the stack was a vent then we could run the lav's trap arm into the stack (we can run a 1.5" trap arm 42" before venting).

Thanks Brent,

It is a single story, I just meant that all the drains tie in below the toilet. Which must be the norm. which makes it kind of seem like a wet vet.

OK wait I'm not explaining it all the way. I think you mean if I went straight across to the main stack it would be OK. But what I,m talking about is draining straight down under the floor than the drain turning horizontaly and travel to the main. Which enter below the toilet.

In this case you would have to run a vent up from your stub out (for the sink drain), using a sanitary tee, and then over to the stack. the horizontal portion of the vent will need to be a minimum of 6" above the flood level of your sink.

DANG!!

Loop won't work?

If you can get it to the original vent you'll probably be okay. just remember the horizontal part has to be at least 6" above the flood rim and be graded level or sloped back towards the drain. you'll have to tie in in the ceiling or attic space. when you say "loop" I assume you mean going up then back down, the vent must always rise.