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Old 05-15-2019, 03:37 PM   #1
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Closing/plugging old furnace vent in roof

I have 3 roof vents I'm going to attempt some fixing of.
The first one I just need to remove it, plug the hole, and put shingles back over it.
The roof was replaced almost 2 years ago, and I have at least 15+ extra shingle panels from the left over open box when they were done.
The furnace was just moved the garage a couple weeks ago, so now I need to close up the old vent for it.

What's the best process for doing that?
I'll have almost no clearance to get there from the attic side, and prefer not to go in the attic anyway.

What I'm thinking...
Remove the one or two panels of shingles around the vent area.
Remove the vent.
Attach a couple 1x2 strips on the attic side by extending beyond the vent hole, and screws from the roof side to hold them in place.
Cut some plywood to match as close as possible the size of the vent hole.
Screw it to the 1x2's from the top side.
Nail new shingle panels back down without the hole cut in them.

Do I need to use mastic around that plug to help seal it before covering with the shingles?
The roof was done with Certainteed Diamond Deck underlayment - but I haven't found yet if I have a place to buy that.
How big of a piece of underlayment should I be putting back down in that area to cover it up, and okay to use any brand for this fix?
I'm assuming if I then have a leak in this area, warranty is void for any damage because of it.

While it would seem unlikely anybody would be in that area and step right there, it's not guaranteed that somebody wouldn't at some point in the next 20 years.
Will this way of closing it with the 1x2's and the plug, etc... be considered an okay way to have closed up that hole?

Anything else that needs to be considered and/or done to do this in a good way?
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Old 05-16-2019, 06:07 AM   #2
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Re: Closing/plugging old furnace vent in roof

Asked a similar question a while back and some replies were provided here: (post #15 probably best answers as to method)

I finished this recently, and as I was replacing the roof, had it stripped down to the sheeting (OSB in my case). As was mentioned in the thread I linked, the proper way to do this is to cut a large enough hole so that your patch spans several roof trusses so as it is well supported. As you are doing this after the shingles are already laid, you may have to do as you suggest and simply block the hole from below and then attach your patch to that, and as to what to put over the patch on the roof side, a piece of ice and water shield could be cut ~12" bigger than the patch, and that could be placed over it and secured to the underlayment. These I&W shield products come in 36" x 65 to 70' foot rolls and as you only need a small piece, you could try contacting a roofing contractor and see if they will supply you enough for the patch.


Last edited by jurgenk; 05-16-2019 at 06:14 AM.
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