Installing bath roof vent


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Old 04-15-21, 10:38 AM
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Installing bath roof vent

As soon as weather permits and I can get some help, I will be adding bathroom roof vent. Bought an Imperial Premium 4" from Lowes.

Although I'm confident about installing the unit, thought I would solicit any possible hints from others.

One thing struck me in the instructions. They state not to add any roof cement to the down side or lowest side of flange of the shingles. Seems odd not to.

In this particular install the fan is located directly below the roof location for the vent and will only be at most 2 feet up. Any reason I can't use hard vent pipe instead of flexible duct? I'll use a flex elbow on either end to align the duct.

EDIT...What type of screws would you recommend.
 

Last edited by Norm201; 04-15-21 at 10:56 AM.
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Old 04-15-21, 10:59 AM
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Hints:

I at least drill a pilot hole from inside the attic. That way you can see where your ducting is inside and where the rafters are located. If you do a small pilot drill in the attic leave the drill bit sticking up through the hole or shove a piece of wire through so you can see it from above to drill the big hole.

Do not seal the bottom side like they recommend. That way any water or condensation that gets under it can drain away. You can seal the bottom side of the bottom side of the flange to the shingles below if you want. Just imagine water and you want to give it somewhere to drain.

Steel duct caps eventually rust. I paint the vent with black rubberized wonder leak stopper in a can or brush on oil based paint as an extra layer of protection.
 
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Old 04-15-21, 12:01 PM
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I at least drill a pilot hole from inside the attic.
Yes, that much I anticipated.
Never thought about rust on metal duct work. I'll just stick with semi ridged aluminum.
So your saying don't implant the vent into a layer of roof cement? But I can cement the shingle to the flange down side? (See step 3 in diagram)


 
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Old 04-15-21, 02:01 PM
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No, not rust on the ductwork. The hood on the roof will eventually rust so I like to give it an extra coat of something before installation.
 
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Old 04-15-21, 03:05 PM
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OK, I understand. _____________________________________
 
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Old 04-15-21, 04:01 PM
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Typically its preferable if the duct is near the ridge... less likely to get completely covered with snow where the wind can clear it off. When ducts turn to go straight up, I will always use a tee as (hopefully) a condensation trap. You cap one end of the tee (the trap), the duct comes into the side of the tee and makes a 90 degree turn before exiting out the roof.

Other school of thought is to keep the duct low on the roofline so that the ductwork can be kept buried in insulation... and its low enough to rake the snow around it, if needed.
 
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Old 04-15-21, 04:18 PM
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So maybe that's why the fan connection is not straight up, but off to the side. So one must use and elbow or bend the flex duct for a condensate trap of sorts. The idea of a tee is a good one. In my case the vent will be close to the edge of the roof. Maybe about 4 to 5 feet from the gutter. This bathroom is on an outer wall.
 
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Old 04-21-21, 07:36 PM
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A little more in expense but a lot easier to install. Get a 4" insulated flex duct. Install, tape and zip tie the flex duct. Drill the pilot hole in a location where you can easily work. Getting too close to the bottom of the roof edge is inconvenient to work. Reinstall the insulation around the fan when finished.
 
 

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