I need to widen my bathroom. The wall next to the toilet and sink will be move back 3 ft.
Do I still need to run the vents straight up the roof or can I use a 90 elbow and run under the ceiling 3 ft horizontally to tie into the old vent that goes straight up.
Thanks

You can connect the vents but not horizontally. The vent must have a down slope back to the main. Use a 1/8 elbow, not a 90 degree at either end and that will be adequate for the distance

In my area you can tie tie vents together in the verical or horizontal with regular 90s, so I'm betting you will be just fine with your original thought.
ma0641 is correct in that you should slope the vent back towards the drain(about a 1/4 inch per foot). Good luck and please let us know how things go.

Thanks

Thanks