Need help installing roof vent for bath fan!

Old 08-16-01, 10:09 PM
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Hello all,

I am smack dab in the middle of a bathroom remodel and, having finished the rough-in of the plumbing, electrical and framing - now need to install the bath fan and roof vent (among LOTS of other things - whew!). Fortunately, the bath is upstairs and directly above it is unused attic space, which makes for easy work above. Unfortunately, there are no soffits in my 75-yr old house and the closest end of the gabled roof is 20' away, so I'm guessing I should just go straight up out the roof with the exhaust vent. (which would only be about 2 feet long) We have a single layer of asphalt shingles. Although I fancy myself as fairly adept at new remodeling projects, cutting a hole in my roof is a bit worrisome for a non-professional like me (absent this forum's wonderful advice, that is). I've got my nice Broan fan and am ready to install the exhaust vent out the roof, but am looking for some guidance on how to go about the process.

Should the vent pipe run straight up from a 90 degree elbow attached to the bath fanís 4 inch side exhaust port?? Assuming this is the preferred method, Iíve been told to then hammer a nail through the roof from inside the attic at the center of where I want the bath fan to exit and then mark a 4-inch circle with a pencil on the asphalt shingles on the roof.

If this is the way to go -- I'm wondering if the 4 inch hole should be oriented with the pitch of the roof OR should it be oriented straight up and down (meaning the actual hole in the roof would be oval in shape) so that the vent sits upright on the sloped roof. I would think it would be oriented with the roof (meaning it's a perfectly round hole) and then the vent goes into the attic at whatever angle the roof is at. Is this right?

I was then planning to remove the asphalt shingles and roofing felt with a utility knife along the newly marked 4 inch circle. After that, I would then use a jig saw to cut out a 4 inch hole in the roof sheathing. Sound good so far??

This is where Iím not sure what to do next? First, any recommendations on types/brands of upper roof vent cover flange. Not sure whatís best, whatís bad Ė I donít want squirrels getting in it (of which there are TONS in our 75 year old neighborhood Ė oh how they love our walnut tree and oak trees) nor do I want there to be a backdraft into the bathroom.

Next, for the vent pipe itself - is a solid wall vent pipe (rather than a flex pipe) best? The fan has a 4-inch pipe exit on the side of it, and I planned to attach a 90 degree bend directly to the fan's exit flange and then run a 4 inch smooth metal vent pipe strait up to the roof.

Third, since I haven't seen a vent cover flange I'm wondering about where the vent pipe meets the vent cover on the roof - does the vent cover flange extend down into the attic and then you attach the vent pipe around it with a clamp?

Fourth, what type of caulk/roofing cement to you recommend for sealing around the roof vent.

Finally, I'm not exactly sure what I need to be aware of when installing the roof vent, as far as specifics on how to attach it to the roof, how to overlap shingles, will I need to put in new shingles, what type of roofing cement is best and where and how should it be applied? Whew. Sorry for the questions on this one - I have no idea on what length of galvanized roofing nails or where to nail them into a shingle, etc. etc

Anyway sorry to carry on about what is probably a simple issue for others. Any comments or help would be greatly appreciated. Thanks in advance.
Old 08-18-01, 05:38 AM
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what is it they say---mountain out of a molehill?cut the hole,round or oval as long as your pipe fits through it flex is fine and its easier.find a vent cap at where ever you buy that kind of stuff-lowes etc.take up your shingles where the hole is and put it on.1-1/4 nails are fine get some black plastic roof cement in a tube saves a big mess compared to a can or bucket of roof cement.just read somemore of your question maybe you should get someone to do it for you -don't want to ruin a nice remodel job with leaks do you?

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