I am having work done on a house and it includes a washer/dryer closet that will be next to an existing bath which is also being redone. The dryer vent pipe needs to go about 8 feet across the ceiling above the tub and toilet to reach the exterior wall and vented to the outside. I was thinking of just running it along the corner of the ceiling and wall above the bath and toilet (the ceiling is high enough to do that) and having it boxed in by building a soffit(?) around it.
One contractor said that since the ceiling will be open anyway, it would make more sense to run it through the 2x8 ceiling joists which run perpendicular to the way the vent pipe will run. That would leave it hidden in the ceiling instead of having a soffit showing. My concern is that drilling 4 inch holes in the joists would create a structural problem since there is a room and floor above that. He said it would be okay because a sister joist could be added to each existing joist where the holes would be.
Does that seem okay as a way to go? It is more work and would cost more up front, but I am not worried about that part. But, would the sister idea be okay, and do the sister joists need to go the whole length of the joists, or could they just be a short section that is sistered on to make up for the holes being cut into the joists?