My brother and I are adding a handicap bathroom to the first floor of our parents house. It will be installed on a one story addition my father added. The problem is venting the fixtures. There will be of course a Lav, a toilet and a shower basin in that order toward the soil stack which lies perpendicular and below the new drain run. The new Lav which is the fixture farthest away is about 10 feet from a 4" soil stack.

If we run a tradition vent stack it will come out of the roof in front of a bedroom window. We are to far away from the original vent stack to tie in.

There are currently four fixtures, a kitchen sink and an upstairs bath(lav, tub, toilet).

Do we need a separate vent stack for these new fixtures or can we dry vent?

Thanks

The group will have to be vented, by "dry vent" do you mean a AAV(air admittance vent)? Most bathroom groups are roughed in like this.
Toilet connects to sewer main or the stack vent. Lavatory connects to toilet drain and runs a vent off the top the stubout tee out the roof or revents back into a dry vent in the attic.. The toilet wet vents through the lavatory vent and the tub/shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes and also The Standard Plumbing Code Book in 90 percent of the country. Check your local codes.to make sure you're not in the excluded 10 percent.. The vent off the lavatory may be run out the roof or the side wall. If local codes allow a AAV may be used as the lavatory vent for your group. The kitchen sink may be revented back to the groups vent instead of running out a separate vent but it must be vented. Good luck, Tom