venting bath fan through roof

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 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 (which will only be about 2-3 feet long) with the exhaust vent. 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. Where do I start and what pitfalls do I need to be aware of as I undertake this. Look forward to your comments. Thanks in advance,

Mark in KC

 

From in the attic, nail a nail through the roof sheathing in the center of where the exhaust fan vent should be.
Go up on the roof, mark a circle a bit larger than the exhaust vent line around the nail, drill a pilot hole on the inside edge of the circle, and cut out the roof sheathing with a jig saw.
Install the upper vent cover flange edge under the shingle above and over the shingle below, and you can caulk or use roofing cement under the edges of the vent cover for added weather-proofing. Dress it up with shingles around it.
Duct tape a batt of insulation around the vent pipe in the unheated attic to prevent condensation from forming and running back down through your fan in the winter.
Good Luck!

 

Thanks Old Guy, that sounds pretty straight forward. Couple other questions/clarifications.

First, do I need to remove any of the asphalt shingles prior to marking the circle around the enter nail or prior to drilling the pilot hole and cutting the larger hole with the jig saw? Basically, I'm wondering if all this is done while leaving the outside roof in as is condition.

Second, any recommendations on types/brands of upper roof vent cover flange, as you call it?

Third, for the vent pipe itself - is a solid wall vent pipe (rather than a flex pipe) best? The fan has a 4inch 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.

Fourth, 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?

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

Finally, I'm not exactly sure what you mean by "dress it up with shingles around it" Will I need to add new roofing shingles after I cut out the hole for the roof vent? If so, what do I need to be aware of in nailing new shingles up? 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... If you can answer the other questions, I'll try to find out more info on this last one before I ask any more on it.

Thanks again for the helpful comments. For an "Old Guy" you sure seem to be pretty on the ball. ;>)

best regards,

Mark in KC

 

1. It depends on the layout of the shingles. Raise the shingle above, and remove the shingle at the cutout, or cut and roll it to the sides, if you can.
2. There are various vent covers (usually flat with the exhaust on the down side). See what is available that will compliment your roofing (or you can paint them, as I do).
3. You can use either type, smooth or flex.
4. You should be able to clamp the pipe to the vent cover.
5. Black plastic roofing cement will last the longest, but wear old clothes and a throw-away rubber glove with it. It is very sticky. Apply carefully with a paint stick or throw-away putty knife.
6. By dressing it up, I mean cutting the shingles to fit around the vent cover. Depending upon what you're dealing with, you may need a matching shingle or two, or none. If you have a standard 3-tab shingle, you nail it just above the slots with 1-1/4" galvanized roofing nails (4 nails each = two ends and two slots).
You'll see and figure a lot of this out as you do it.
Good Luck!

 

Hi, Good advice so far. It all goes together pretty straight foreward. A little hint from me is to cut the shingles with a utility knife first then cut the wood with a saw. If you don't it will make a mess out of your skill saw and ruin any blade you use.Good Luck Woodbutcher

 

Thanks Woodbutcher! Good advice! I'm assuming you're talking about after I've nailed up through the roof and am marking the 4inch circle for the vent on the roof.

Basically, I should:

Mark it on the shingles, then cut them out (and the roofing felt) with a utility knife. THEN, drill a starter hole along the edge of the 4 inch circle and THEN use my skil saw to cut the 4 inch hole out of the roof. Does that sound right??

THanks again!

 

One other quick question (which may seem silly, but maybe it's the beer talking....oh, wait it's only THURSDAY night..no beer yet, darn, guess it IS a dumb question) Anyway, I found another lil quip online where the guy suggested that the vent hole cut in the roof should be oriented straight up and down. So now 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. Assuming this is the case - how do I connect that angle with a vertical 4 inch vent pipe? I don't think this is going to fit a standard 45 degree elbow. Thus, am I relegated to using flexible vent pipe and, if so, is that going to work fine? I had heard that smooth solid aluminum vent piping is much better for the airflow. 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.

Mark in KC

 

Hi Again, Your last post was correct. Cut the hole bigger than the pipe so the pipe will be plumb not perpendicular to the roof, hole size isn't too important just make sure the pipe fits through the hole and the roof jack covers the hole. Good Luck Woodbutcher