Attic vent flashing on metal roof

How would you properly flash this vent?

This is how our installer did it. I don’t like the way it’s lapped. If water gets in from the top side, it will leak under the panels.

He did it this way because the flange on the vent was too thick (1/8") to bend around the ribs, so you can’t easily get it to sit on top of a panel. He caulked it well, and the bottom of the vent sits over the underlayment (bubble foil) so if any water does get in, it should run out the eaves. But I don’t like to rely on caulk (or underlayment) as a permanent fix.

I found the manufacturers instructions -link- which show to cut the ribs below the flange so the vents sits closer to the deck. But that seems sketchy too. You’re just relying on caulk to seal the ribs now.


  • Leave it as is, address it in the future if it ever leaks.
  • Rip it out and reinstall follow the manufacturers video.
  • Remove just the top panel and add additional flashing to direct water around the vent.
  • Any better ideas?

I’m no expert in metal but if just caulk on expandable metal is kinda retarded, maybe put bottom half of fan flashing on top of roof and upper half get custom covered with matching ribs for similar looks ,just like shingles but in metal
Real metal guys should pull up soon tho :grin:

That’s how he normally does it. Pieces would be installed/lapped in this order.

Lower metal panel – vent – upper metal panel.

Everything overlaps, so you need to conform the vent metal to the ribs in order for the upper panel to fit. I can’t think of a good way to install a top panel, or even custom flashing, if the vent is sitting completely on top of the ribs.

The flange of the vent is a complete circle (about 3" larger than base). That makes it hard to sit properly on the ribs too.

More pics please!!!

So far, i am
Sitting here admiring this roofers work.
His use of the “double bubble” underlayment/ insulation.
And the way he is using almost a standing seam fastening technique.
I am loving this roofer and i want to see more.
Is that how this manufacturer is describing to
Fasten the panel?

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I can get you photos, but to answer your questions.

  • This is a layover installation over shingles, the bubble underlayment helps it sit flatter.
  • The panel manufacturers instructions say to screw through the lows unless you have a shallow pitch (then screw through the ribs). However on a layover, screwing through the lows has a potential to dent the metal.

Yes, more pics please.

Yes this double bubble has the added benefit of a flatter roof because the fasteners sink into it
And so it it flushed.
No sticking up fasteners for the metal to dis form over it.

But its main purpose is to keep the heat out!
And i can attest, it is awesome.

There is still some detail and trim work to do.


Good looking job.
Good looking home.
Nice color selection.
Nice roofer selection.
Well done.

Definitely. No issues with anything else. My only concern is with the vent.

Currently, it’s relying on caulk to stop water entering the top side of the vent. The ribs even create a small dam, trapping water until it evaporates or leaks in. If it does leak in, it will run under the metal panels but atop the underlayment, down to the eaves.

If this was a shingle roof, this would not fly; underlayment is only a 2nd line of defense. But I know with a metal roof you expect the underlayment to handle some moisture due to condensation. But how much moisture is acceptable.

Personally, when i need to flash a large penetration on that style of roof I run a large flat sheet called a “backtray” around it which goes all the way to the ridge. This goes over the sheet and provides a flat surface which is far easier to flash. This isn’t my work, just an example i found via a quick google search.

On commercial jobs I fill it with foam to the top of the ribs., trim it to a taper on the high side and coat it with Truco. Roofer can get flat stock of the same color and build a cricket along the same format. A pond is NOT acceptable!

Reverse laps like this can be done successfully, but I would have liked to have seen a gap at the top to avoid the dam and more screws all the way around to stop the metal-metal seam from coming apart. I would not want to rely on underlayment as it is full of screw holes and looks to be above valley. Too bad, rest of the roof looks great!

That is nice and clean work. Anything we do like that is always installed on a curb to get a standard flashing detail

Thanks for the help and ideas. We ended up building a pan under the bottom of the vent. Sort of an improvement on the manufacturers video.