A friend was living in a fairly tight condo and complained that smells would come from vents in kitchen and or bathroom.
Outside three vents were side by side rand hood bath fan and dryer. With a tight building air has to come from some where to feed the fan. So cooking smells would come in thru the bathroom and the other way was not so pleasant.

 

Without dampers in each line at the junction to prevent back gassing into the other bathroom, I'd say no.

 

So they could put one of these on each side to keep one side from going to the other?
4" Backdraft Damper, Balancing Barometric Backdraft Butterfly Damper Draft Stopper Backflow Preventer (4" / 100mm) - - Amazon.com

I had two bathroom fans going through the roof, but re-routed them out the side of the house instead before I had the roof replaced 5 or 6 years ago. But I just kept them separate, and wanted to get rid of both vents out the roof. I like less holes in the roof, and also wanted fewer things on the roof so it was easier to do solar without having to work around them.

Cutting through that stucco on the side wall was fun

 

Thanks. So what I am going to do is go ahead and run the vent for the master bath fan (large fan basically over a large shower) up through the roof and leave the hall bath fan (smaller fan) venting out under the eve. It's a 3" duct but when the house was built in 1996 they just ran the fan ducts to the edge of the eve, not through the soffit, so technically venting into the attic, but the air pressure from the fan pushed the air flow the last few inches out the soffit vent (no mold on underside of plywood roof sheathing). Must have been ok back then given town inspector passed it, but I never liked it. Same with laundry room. I will get a couple of 3" under eve soffit vents so they vent through the soffit.

Any particular through the soffit vents you guys prefer ?

Thanks again.

 

If your soffits are perforated for attic venting, exhaust will still be able to drift back up into the attic.

 

They're not continuous perforated, just have 4" x 16" vents every 4'.

 

Or you could put in a soffit vent if the other perforations are not close by.

 

So I did a lot more work on this today, What they did was run the 3" aluminum flex duct into that soffit stud bay and then sealed it off using spray foam. So I guess that's how they got it as not exhausting directly into the attic. I removed all that and now it's just another soffit vent. I will now vent the 2 bath fans, one 3" and other 4", up through the roof separately.

 

So this little project just keeps on going. I went out today to a bunch of new construction $500k+ homes and found this. As you can see, they ran the master bath fan duct and master bath toilet room fan (fart fan) into the same roof vent (square one in the 2nd pic) and sealed it all up = vented directly to the outside per Code. Code doesn't say how you have to achieve this, just that you get it the outside. I unfortunately didn't get to see how they did the under the vent attachment - anyone know ? This does get me one hole in the roof for two fan ducts. Thoughts ? In the bottom pic the higher vent is for the dryer vent.

 

I don't know if this makes sense for you - I only share in case it triggers any ideas on how to do things.
And the bathroom vents I did to the side wall might not be to code - I'm not sure what code is on that.

But this is what I did...

I wanted the bathroom vents and general vents off the roof.
So on the roof re-do, I went with ridge vents on the roof.
And I moved the bathroom vents to the left side of the house.

I used these vents on the outside wall for the bathroom vents going out the side.

HVACQuick - Seiho SBP and SFBP Series Aluminum Dryer Vents with Backdraft Flapper and Tail Piece

Is it the right way to do it - I don't know.
Is it to code, I don't know.
But it's what I did.
I wanted fewer holes in the roof, and wanted fewer things on the roof for the future solar panels to have to work around.
I'm a little OCD on that side of things - when the solar panels are all crazy having to work around the various vents, that drives me batty.

So, it's what I did - comments welcome on what I screwed up on in doing it this way

Roof with vents before -

New roof after with vents moved -

Bathroom vents out the side -

 

Nice work gthomson ! Code does not dictate that the exhaust has to get outside via the roof or wall, just that it gets outside. Like you, I don't like holes in roof but I don't have any gables I can use to get it out that way.

 

I wanted to run this by you all as a possible option for terminating my 3 bathroom exhaust fans. I'm not thrilled about putting any new holes in the roof, and drilling 4" holes through the brick veneer doesn't thrill me either. Out my back door I have a patio, part of it is covered with HardiePanel as you can see and from there is a large pergola. Any issues with simply running the semi-rigid flexible aluminum duct from the fans to this area and out through the HardiPanel ceiling here ? Thanks so much.

 

I was out at a local jobsite just now where HVAC guys are working. I was able to see how they terminate the bath fan duct through the roof using a standard square roof vent. They're using flex duct and just use the 4" hole in the roof sheathing to hold it in place and then fully secure it with duct mastic to both hold the flex duct in place and seal it off to the underside of the roof sheathing.

So I think I'm going to basically do the same thing but take it up a notch using something like what I have mocked up in the pic below. I'll bend the tabs on the collar to more solidly secure it to the roof sheathing with some adhesive. I have 2 fans so I'll cut two 4" holes in the roof close enough to each other so that the one standard roof vent covers them both.

Any advice would be appreciated - thanks so much.

 

So I went up on the roof this afternoon, funny, I reroofed my house in Chicago but it was only a 4/12 pitch and although my house here is "only" a 6/12 pitch, it's still just too steep for my comfort. I asked 3 local roofing companies for an estimate to just add either 1 standard 10" slant-back vent or 2 small 4" vents. Another option is for me to get a 16' straight ladder and ladder hook, that seems doable. Any other SAFE way for me to do the roof vent install ? Thanks so much.

Oh, any idea on what they should be charging me to add 1 vent (or 2) thx.

 

Wow - got several quotes fom local roofers over the past week, I couldn't believe it, all were in the $400 - $650 range = DIY.

I installed 2 separate Broan roof caps this morning and just finished the flexible duct connection to hall bath, very easy job. Will connect up master bath tomorrow. Oh, I also added a piece of rubber ice/water shield just to be sure.

KEY - make sure to seal all connections, at the interior roof deck and at the fan duct connection, with the 1030 Gray sealer, even when using aluminum foil tape , zip ties, etc. First I just sealed the interior roof deck connection but after sealing the fan connection too, all the air leakage was gone.