I'm looking to install a bath fan (https://www.homedepot.com/p/Delta-Breez-GreenBuilder-Series-100-CFM-Wall-or-Ceiling-Bathroom-Exhaust-Fan-ENERGY-STAR-GBR100/204347760) in a bathroom on the second story.

The bathroom doesn't have the attic over it though, and there is about 1' to the roof.

My question pertains as to how to mount the fan though. The manual (https://images.homedepot-static.com/catalog/pdfImages/af/af6d5071-25ee-4203-8969-8983c5237ae3.pdf) assumes that this is "new work" or that the attic is accessible.

Brackets were included in my box, but I don't think I'll be able to use them since the rectangle I'll be cutting is the length of the fan (about 8").

I noticed that there are holes in the side of the box (Marked in the picture) in the picture below. If the fan was placed against one of the joists and then screwed into place from below using the screws provided through these holes, would this be an acceptable technique?

Fan Diagram Actual Picture

1 Answer 1


Are you going to install a roof vent? If so and the ceiling is only 1' away, you can probably reach in through your 4" roof vent hole and screw into a ceiling joist or rafter tie to mount.

If you are going to vent directly into the attic and avoid cutting the roof open, you may run into problematic mold issues. If you're determined to go this route, your technique of screwing through the enclosure or drilling new holes should hold the fan adequately. The enclosure, aside from the electrical junction box, can take the screws. Remember you can and likely need to pop out the fan to get good access.

  • I plan on installing a roof vent. If I can't reach (The operating conditions are rather limited with 5"). I'm thinking of (cut hole in bathroom -> drill roof marker in bathroom roof -> run ducting to marker -> install roof vent (which I can do since I left the ducting so close to the marker) -> electrical wire up -> attach ducting to fan base -> secure fan to joist using screws through body of fan) Dec 29, 2018 at 1:51
  • I agree it's a tight fit. Getting all the ducts taped will be challenging in the space, especially if want to avoid having too much bend in your duct. But yeah, screwing through the enclosure instead of through the flange is mostly fine. You might end up with a bit more give in the squareness of the enclosure, but it won't be problematic in practice.
    – Steven
    Dec 29, 2018 at 2:24
  • Yes, I was thinking about how much force each screw holds when properly tightened and realized that 4 of them could probably hold >50lbs no problem, never mind the 5 lb bath fan :D Dec 29, 2018 at 6:04
  • The screws or their ability to hold to the enclosure shouldn't be your limiting factor. A single screw into wood against a metal frame can easily hold hundreds of pounds of shear and pull strength. The thing that will likely "fail" first is the rigidity and squareness of the frame, but your photo makes it looks pretty thick. A nitpicky electrical inspector might take issue to the box not being secure enough, but I suspect you should be fine. Good luck with the project!
    – Steven
    Dec 30, 2018 at 23:13
  • I screwed it in with 3 screws in the triangle formation (there was a third screw hole behind the fan shown and it was above the line between the two screws in the picture) on the box. It made the frame rather sturdy but required the removal of the fan (Which wasn't that bad). I just need to adjust the ducting a bit (I think I might have taken too hard of a turn with the ducting, but all in all it turned out pretty well. There was a vastly lower quantity of humidity after my shower. Thanks! Dec 31, 2018 at 2:21

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