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Leaky metal roof: I got questions for This Old House
Posted by: deckeda
Date: February 12, 2018 08:37AM
This old house had an extension built onto it years ago, and then an entirely new roof structure was created on top of the whole thing. Topped with a metal roof.

I’ve been up in the “attic” crawl space to take a cursory look. The only access is via one of those pull-down stairs in the ceiling. It was installed in what used to be part of the old roof, so when you get up inside there, you’re standing on asphalt shingles ...

Those shingles/false roof have revealed where leaks are. The roof frame and metal roof can be seen. Some water runs off to who knows where, some evaporates before becoming revealed, and one water trail runs into a bathroom.

At least one bath vent pipe leaks. Seen that water coming down the outside of the pipe while up in the crawl space during heavy rain. The pipe emerges up from the old roof just as you’d expect of an asphalt roof, complete with flashing/flange, and extends up through the metal roof. I have no idea yet what it looks like up top, but have reason to suspect it looks like a big glob of roofing tar ... that’s how my father in law has worked it before.

Questions:
Is there a metal roof specific flashing or flange I should be aware of, if it’s absent? Pipe is PVC, about 1.5” or 2”.

What’s the best way to fix the other, random leaks coming in from the screw holes? (I say “screw holes” but for all I know they could have nailed the metal roof on.) Waiting for a dry day to inspect.

Replace the screws? Replace ALL the roof’s screws? I once took a day job as part of a gang that spent an afternoon on top of a metal roof (commercial building). All we did was replace the screws ... boss who hired us said it gets done every year as preventative maintenance?
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Re: Leaky metal roof: I got questions for This Old House
Posted by: Michael
Date: February 12, 2018 09:29AM
I believe there should be rubber gaskets around the screws--at least my friend's metal roof has them. If so, I'd replace those on the ones that are leaking and see what happens. If not, I'd stick rubber gaskets around those leaking screws.

For the leaking vent pipe, our roof is 27 years old and the vent gaskets degraded and 1 started leaking years ago. When that first happened, I went to Home Depot and bought new ones and then simply slipped them over the old ones without removing the old ones because I didn't want to pull up the shingles to take the old ones out--afraid I'd break the really old shingles. That gave me a new gasket and the rain would simply run off the new gasket. I re-replaced all of them this summer, cutting off the old ones and slipping new ones in place. It doesn't leak.

I'm going to have to replace the roof one day but I'm trying to hold out to see if the Tesla solar roof really becomes a thing.
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Re: Leaky metal roof: I got questions for This Old House
Posted by: billb
Date: February 12, 2018 10:25AM
Stinkpipe flanges for a steel roof are supposedly a pita just like chimney flanges.
You really have to get up there and see what has failed, the flange itself or gasketting. Tar and other goops dry out and crack, subsequently leaking.
Replacing the screws on the metal roof was likely replacing the rubber washers that dry out and crack in the sun and heat.



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Re: Leaky metal roof: I got questions for This Old House
Posted by: Ombligo
Date: February 12, 2018 10:49AM
Fastest, cheapest, will last a few years repair - go to the area that is leaking and put a dab of silicone on all the heads. You can also run a bead around the pipe.



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Re: Leaky metal roof: I got questions for This Old House
Posted by: nwyaker
Date: February 12, 2018 12:04PM
Remove/replace leaking screw and put a dab of polyurethane under ( 3M 4200 or Sikaflex 291/292 ).
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Re: Leaky metal roof: I got questions for This Old House
Posted by: Carm
Date: February 12, 2018 02:30PM
Movement around the area might disturb the other screws on the sheet of metal. Whatever is within reach should also get a dab of what you are putting down.
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Re: Leaky metal roof: I got questions for This Old House
Posted by: deckeda
Date: February 13, 2018 09:54AM
Thanks all.

The vent pipes do not have any flashing. Only roofing tar gooped around their base where meets the roof metal outside.

Just now in the store I see they sell rubber rain collars for vent pipes. I could rework the goop, which is effectively my flashing, and place the collar over the pipe to shield the goop and help rain run away from the pipe, not down it’s sides. And then count on replacing them as maintenance, as opposed to a silicone bead on them, which isn’t permanent anyway.

I have only today to deal with this before a solid week of rain comes, and it’s likely too cold for new goop or caulk to adhere well.

[Edit] Found some stuff made for this, and to be used on metal roofs. Says it can be applied hot or cold, so up again I go.

Got the rain collars on but they can't be slid all the way down due to the hardened roofing goop and also due to some pipes coming up through the peaks, not flat parts of the metal.

The screws I took a quick look at. They have the requisite integral rubber washer but they do look old. Rather than try and daub some silicone all over them I think it makes more sense to remove and replace them ... as anticipated. I hate ladders and roof work and will have to hire a team to get that done. Sounds familiar.



Edited 1 time(s). Last edit at 02/13/2018 12:05PM by deckeda.
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Re: Leaky metal roof: I got questions for This Old House
Posted by: billb
Date: February 13, 2018 12:09PM
Roofing tar is good for a year if that.
IMO, it's temporary. Or old school get up there on an annual basis, scrape the old dried up and cracked tar out and dribble new hot stuff in every Spring.

Silicone needs clean surfaces to adhere. You might get a good compression seal with it like a gasket, but if there are any dimensional changes going on ( as with day/night temp changes) it will leak right past where it hasn't adhered to dirt or atmospheric oils on surfaces.



The Phorum Wall keeps us safe from illegal characters and words
The doorstep to the temple of wisdom is the knowledge of one's own ignorance. -Benjamin Franklin
BOYCOTT YOPLAIT [www.noyoplait.com]
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Re: Leaky metal roof: I got questions for This Old House
Posted by: deckeda
Date: February 13, 2018 03:25PM
If I get a year out of this fix that'll be enough. I won't be in this house in a year's time. And at any rate, the rain collars won't hurt since I noticed the weak areas of the goop where it meets the pipe, as water of course ran down the pipe. The collars will help prevent that.

I will however begin replacing the roofing screws this spring. Thanks again.
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