I don't buy the logic. What difference if is is one larger penetrations versus two smaller ones.

Are these 6-inch ducts? I see a lot of daylight around the hole in the roof. How is this going to be capped?

I have two bathroom fans connected to separate 6-inch ducts. For each one, a 6 inch round hole was cut into the roof. There is a roof cap on each. The cap has a 6 inch round metal piece which comes through the roof. The flexible ducts are attached to this. Roof caulking is used to make it waterproof.

I suggest you added insulation to each vent. This will prevent moisture building up inside the duct and dripping back onto the exhaust fan.

I have a total of 5 exhaust fans. 4 of them are connected like this (2 large openings plus 1 small one with only 1 duct). They all are 4" ducts. I only see the metal roof jacks used. What should we do to fix this now? Contractor only mentioned about spray foam around the gaps.

Thank you!!

Forgot to mention that the location is San Jose CA area. How important is it to insulate the bath ducts here?

How is the contractor going to ensure the roof doesn't leak? I have never seen spray foam used to seal a roof connection. I am not expert, but I would be nervous if this was my roof.

How cold does your attic get in the winter? You may not have a condensation problem. You should ask the contractor about the normal practice in your area.

In San Jose, I wouldnt think that insulating the ducts is necessary.

I have something similar to this on my roof. Not a problem as long as the cap used is big enough. There is no cap here in this picture, hence all the daylight.

Personally I think the fewer penetrations through a roof the better.

I also don't see anything inherently wrong with venting two bath fans through a single roof opening.

Even if both are on at once, probably the worst thing that will happen is that they back pressure each other and they don't vent quite as efficiently.

Both of my bath fans are vented through the same soffit vent.

I am concerned about the cap that you all mentioned. This is what I have now:

{{gwi:1549822}}

Those two on the left are bath vents.
There is no round metal piece for the duct to attach to. Is this good enough?

Anyone else has more suggestions or comments?

I have a square ventilated cap. The duct does not need to attach directly to the cap.

So the flex ducts you have pictured in the first picture are both terminating into which roof vent in the 2nd picture?

Right, those two flex ducts both terminating into the left most roof vent in the 2nd picture. There are two more ducts going into the middle roof vent...

I was planning on doing a similar thing, but I would join the vents from 2 fans in adjacent rooms with a Y connector so the two would merge into one and there would only be one duct exiting. Is that a workable solution?

I read somewhere here that joining ducts from two bathrooms may not be a good idea because the two bathrooms will be 'connected'?