Hello, I'm putting a bathroom in my basement and wanted to see if I was on the right track for my waste and vent plan. The bathroom will have a toilet and shower on one wall and the lav sink on the opposite wall. There is an existing drain line that runs from the sink and dishwasher above that goes to the sewer and is vented to the main stack of the house. My plan is to tie into those. At this point, I am hoping someone can let me know if I'm on track with the general design. Here's what I sketched out...I'd appreciate any help you can offer. The part I shaded in blue are the existing lines.

Even though this structure is within 6" of the primary structure and the drain lines are connected, none the less, it is a separate structure and will require the 3" vent through the roof. I received your drawing and have reviewed it. The dimensions are close enough that you will only require one vent for the bathroom group, that being a 3" vent through the roof as mentioned above. You have two 3" openings however a watercloset may only be installed on the end of the line, it may not be installed over a TEE. You would need to look down in the pipes to determine which one is on a tee and which has a long radius elbow. The toilet MUST BE installed on the one with the elbow. The drain for this structure is tied into the main structures DWV system so the position of the watercloset should be the 3" which is furthest away from the main structure. When you install the 3" vent riser on the opposite 3" opening you could then install a 3"x3"x1-1/2" Sanitary Tee on that riser and run a horizontal line to the lavatory. If you are under the International Residential Code that horizontal line may be up to 6' long when measured along the top of the pipe from the vent riser to the fixture trap. If you are under the Uniform Plumbing Code the maximum length of that horizontal waste arm would be 3'6". Remember, that is the actual developed length of the pipe, not the horizontal distance from the vent to the fixture. From the placement of the 1-1/2" line in the floor it is obvious that it was intended to be for a shower or tub. If you install a tub/shower you may use the 1-1/2" line but if you install a shower stall the code now requires that the drain line for a shower stall must be a minimum of 2", in which case you would need to change that line to 2".

I'm not sure about your proposed solution but I had another thought. It sounds like you have access to the attic. What if you went up there and air sealed around the fan? We are building a new house and I wasn't happy with the fan installation so I used a bunch of quality tape to seal up the connection to the flex pipe and sealed holes in the housing. You could also try insulating the entire length of the flex pipe. Good luck.

AhhHaa,if the jack was desighned for rubber shield,that might fit better than conventional metal collar. At any rate,the space between pipe and jack is normal because (A) The jack also work's for double wall pipe from gas water heater which is a little fatter and (B) The space alow's air space when single wall pipe is hot.