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I have a small bathroom with exterior walls in an area of my home with a vaulted ceiling (and thus no attic access.) When I moved in, the exhaust fan was uselessly "exhausting" directly into a fiberglass batt.

I'm hesitant to cut a hole in my roof to exhaust the fan properly, but if I go a few more feet I think I can access the soffit area and place a vent there. What I'm not familiar with is whether or not I can expect some kind of obstruction between the roof joists over the exterior wall.

Proposed Diagram

This is a rough sketch of what I intend to do - however, before I go yanking the existing insulation out from between my rafters to make room for the flex duct, can anyone tell me if this makes sense? Should I be able to snake a flex duct between the rafters and into the void between the soffit and overhang?

  • Hello, and welcome to Stack Exchange. Good question: keep 'em coming! – Daniel Griscom Aug 24 '18 at 17:53
  • Makes sense to me, but I do not think you need the right angle vent showing on the underside of the soffit. supplyhouse.com/… – Jim Stewart Aug 24 '18 at 18:19
  • @JimStewart Alright, I'll look into what's available. I originally chose the right angle because it's the only "louvered" one I could find that would allow the door to close when mounted in a soffit; I think the "dryer-vent style" ones are all gravity-close on the louvers. Either way that's not a biggie. Thanks for the reply! =) – VanGoghComplex Aug 24 '18 at 18:24
  • At least some of the fan units have the gravity closure door on the fan unit itself. – Jim Stewart Aug 24 '18 at 18:48
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    Mine has that door, and I hear it during stormy weather as air pressure changes open and close it. – DaveM Aug 26 '18 at 3:55
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Welp, it worked just fine!

Welp, it worked out just fine! Still need to caulk it and paint it, but it installed easy and it's amazing the difference a properly vented bathroom makes.

  • I've done a similar thing with my bathroom vents, but I did find an outlet vent that didn't hang down like that. – DaveM Aug 26 '18 at 3:54
  • @VanGoghComplex Would you be able to provide the manufacturer and model of the vent piece with the sideways door you used? – PhilippNagel Oct 25 at 15:54
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This old house has an excellent video on why the soffit location can be bad, and how to put it through a common shingle roof instead:

https://www.youtube.com/watch?v=PqrZWd_CQIE

How to Vent a Bath Fan Through the Roof, August 2014.

The problem with the soffit is depending on climate, warm air heading back up and causing mold under the roof sheathing. This is worst if your soffit is vented in the same area as the bath exhaust.

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