Bathroom vent through existing roof vent

bathroomroofvent

I have a roof with two gable vents as well as slanted vents that look a lot like these one: enter image description here

I do not want to install an extra vent specifically for bathroom so I was wondering if I could use one of the existing top ones. It looks like from underneath there is a circular hole that I can push a duct in. The roof vents don't leak so they are solid even with really crazy rain, hale snow etc.

Can I install on existing vent? If yes, do I have seal it after pushing the vent in so that no humidity will return back down to the attic? What's the best way to go about doing this?

Best Answer

We've got several things going on here:

  1. This is a ridge-mounted, Slant-Back Roof Vent -- it's used to ventilate Attic air to the outside. It should not be used for double-duty for a Bath Fan exhaust. Warm moist Bathroom air will condensate on its underside and can cause moisture damage & mold on the roof sheathing.
  2. As a Slant-Back Vent, the original photo shows it installed backwards. The slanted side is installed to the top to shed rain water; unseen in this photo is the screened bottom side (see attached photo).
  3. As previously mentioned, most building codes require the Bath exhaust to be vented directly to the outdoors. Attic locations should use insulated duct to reduce condensation problems. The exhaust ducts can discharge through the roof, soffit or gable siding -- but a dampered Vent Hood should be installed as well.
  4. If this installation is to be done by an average Homeowner or Handyman, I typically recommend a siding-mounted vent. Retrofit roof vent installations require proper interlacing with roof shingles (not just gobs of tar); a poorly done job will result in a roof leak.enter image description here
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