Howdy y'all, can I get your help with this?

The fan on the master bath vent fan/light combo quit working. The unit is old enough that I can't get a repair part so it's time to replace it with a totally new unit.

It turns out that the original vent fan was just venting to the attic space. There doesn't seem to be any mold growing yet but I'm not able to get a good look due to access issues (described later).

What is the best way to vent the fan to the outside, through the roof or through the gable end of the house? Any tips for doing it without causing a leak and for doing it with the fewest trips into the attic space?

There's a picture of the attic space below.

The attic space above the master bath is under a new roof line added during a room addition. It will be accessed by crawling through a small hole in the old roof. It will suck. I'd like to only make the trip once.

The attic space picture was taken by sticking my phone through a different small hole in the old roof, so sorry for the poor quality.

(Having problems posting pictures at the moment. I'll try again in a bit.)

Attic space over bathroom:
https://imgur.com/a/sR8A37A

Access to second attic:
https://imgur.com/a/UBY3K6v

Hard to tell, but do you have access to soffit? If you do, there are application specific vents to exhaust through soffit.

barnacle bob said:

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Hard to tell, but do you have access to soffit? If you do, there are application specific vents to exhaust through soffit.

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There's no soffit near the bathroom attic. I can get to the sloped roof straight up from the existing vent fan or the gable end to the right of the existing vent fan.

Go out the gable side. Drill a 4" hole (what kind of siding is out there?), install a wall vent termination, tape the flex duct to the vent termination and fan with silver duct tape, for hvac ducts, caulk the exterior around the vent as necessary and you're good.

Going up seems more complicated from the pictures and the longer run is less desirable, plus putting a hole in the roof is less diy friendly.

What's the flex duct that's currently there? Is that from another fan? You said it's connected one end, correct? Or that's the existing duct for the fan that died?

I've see fans installed, no duct whatsoever and insulated over the top of them. Stupidity.

Just a quick tip that I have made a rule.
Never penetrate a roof if you don't need to.

TexAg1987 said:

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Just a quick tip that I have made a rule.
Never penetrate a roof if you don't need to.

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I'll take that to heart!

toolshed said:

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Go out the gable side. Drill a 4" hole (what kind of siding is out there?), install a wall vent termination, tape the flex duct to the vent termination and fan with silver duct tape, for hvac ducts, caulk the exterior around the vent as necessary and you're good.

Going up seems more complicated from the pictures and the longer run is less desirable, plus putting a hole in the roof is less diy friendly.

What's the flex duct that's currently there? Is that from another fan? You said it's connected one end, correct? Or that's the existing duct for the fan that died?

I've see fans installed, no duct whatsoever and insulated over the top of them. Stupidity.

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I've got stucco on the side of the house. It's probably from the mid-80s. Any tips on how to cut through it?

I got a couple of questions about running it out the gable. The vent termination will be over a flat porch roof. How high should it be over the flat roof to keep from damaging the flat roof with the extra moisture? On the flex duct, how do I deal with the issue of condensate running back to the fan? Or is it not really an issue?

One end of the current flex duct is attached to the existing fan but the other end is just laying on the floor of the attic space.

Thanks for the help!

Well, cutting a hole in stucco is a different animal. A 4" circle is going to be somewhat difficult for most people. You could get a wall termination with a larger flange for attaching to the wall and cut a 4" square with an angle grinder. Attach it through the screw wholes in the flange with screws and plastic anchors, assuming you can drill those in without breaking out the stucco near the cut for the vent. Caulk the flange to the wall with a good latex exterior caulk or exterior siliconized caulk. As far as clearance from the roof below the vent, 14-16" should be plenty. If you tuck it higher under a soffit overhang you'll have less issues with rain leaks on the termination as it's protected from most weather.

If you go through the roof, have a roofer there to install the roof termination before hand so it's in place when you go in the attic. Roof is a bit more critical in tucking the flashing right so you don't have a future leak issue.

As far as condensation, most fans ducts are not insulated to prevent condensation. It's a minor issue, but if you're in a humid coastal climate it might be good to put an insulation over the metal duct. Amazon and the box stores have a few options for it.