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Bathroom fan in attic, poly surrounding

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Posted by: from Toronto
10/17/2016 at 7:27:34 AM

Hey all,

I just replaced my roof, plywood and shingles. I have two bathrooms side by side. One was a powder room, other is full bath. I decided to replace both bathroom fans, however because the powder room had some dripping of water in the past, I decided to use a broan ventless model.

My master bath I used a delta model and vented through the roof. During the install I noticed the old powder room one was wrapped with poly, but the ensuite fan was not (never leaked).

Installing the ensuite one I laid poly over the opening to prevent insulation falling through the hole, and then wrapped it up the joist that I screwed the fan housing into. During the install from underneath I cut the poly back. I started thinking it may have been the poly touching the metal housing in the winter that caused the moisture in the powder room.

In effort to try and prevent what had already been done. I decided to place foil tape over the seam between the drywall opening and the metal housing. Does this sound like I did the right thing?

Despite the styrofoam board method what is the proper way to have done this?

REPLIES (2)
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Date/Time10/17/2016 at 12:06:00 PM

Yes, if your bath fan is wrapped in poly and if there is no or very little insulation around it, moisture will build up and cause a leak. If your fan pipe going to the roof is un-insulated, this to may cause a leak, for same reason. Your fan should be wrapped with poly and have a insulated pipe going the vent cut in the roof.

I strongly do not believe in not venting a bathroom fan. One must either open a window or vent moisture outside , if not you will have moisture and MOLD build up in time.

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Nik in Toronto
Date/Time10/17/2016 at 12:24:29 PM

Yea I hear ya. The powder room is just a toilet and sink. It's really not our main washroom. I don't see any moisture issues in that bathroom, I figure to keep things well insulated the ventless one should be good enough at removing odors. Our main washroom we use is the ensuite (full bath).

So it sounds like I did things well, minus putting poly on top of my ensuite bathroom fan. I used a 4" insulated pipe, and actually purchased a Maximum air vent for the bathroom that carries the insulated pipe above the roof into its housing where it exits.

Overall my attic is about an R60 as I did batt insulation plus topped it off with loose fill cellulose.

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