I am adding bathroom exhaust fans. The roof caps I have attach directly to the duct (this is not the model I have, but it clearly shows how the duct attaches):

roof cap with duct attachment

I had a lot of trouble trying to get the flashing slid up beneath the shingles with the duct attached - in fact, at this moment the cap isn't attached to any duct while I come up with a game plan. The main trouble is the length of the duct. This is exaggerated but shows the problem: the complicating factor

Does anyone have any tips or advice on how to do this? It's worth mentioning that I am trying to do this myself, though I am aware that it's normally a two-person job. I can't see how my main problem of not being able to get the flashing slid up between the shingles would be helped with another person, but - I'm listening!

  • Is there any reason you're doing it with the duct attached, as opposed to fixing it to the roof, then coming in from underneath to attach the duct?
    – Joe
    Feb 26, 2011 at 3:47
  • @Joe - at this moment both the fan and roof cap are fixed into position. The duct is rigid, and cut to length, so it's not possible to maneuver the duct without one of the ends being movable. Feb 26, 2011 at 4:52
  • 2
    I think the easiest solution will be to cut the rigid duct into two pieces. Attach them, butt the cut edges together and use HVAC foil tape to join them back together. Since there should be no movement or pressure, this kind of joint will work fine. Feb 26, 2011 at 11:47
  • Thanks @shirlock - I was trying to avoid that kind of "hack" but it is seeming like the only way. I'll look into attaching some kind of support, just in case, too. Feb 26, 2011 at 20:17
  • Sure, you can overlap the taped joint with a spare piece of vent metal. Overlap the joint 3 to 6 inches on either side and pop rivet it (if the metal is thick enough) or use the same HVAC foil tape to secure the splint. You will be amazed how strong the HVAC actually is. Just be sure to get pro quality tape and apply it as evenly and smoothly as you can. Feb 27, 2011 at 12:20

1 Answer 1


As Shirlock says, cut the duct off of the cap, install the cap, and reattach the duct using a 6" scrap piece of metal ducting. Tape any joints with the HVAC foil tape.

Another alternative, remove a bunch of shingles, install the cap and flashing straight in, and then install some new shingles over the flashing.

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