Installing Flue through Metal Roof?

They do make a flashing that has a flat lead bottom that will bend around the ribs in the steel. That and lots of silicone will seal it up. Should put a diverter behind the chimney so snow doesn't build up or slide down and hit it. I'm not a big fan of putting holes in steel roofs. Its hard to seal them up especially when they expand and contract with heat and cold.
Doug

If you can exit at the peak it makes for a clean install. Here's how I did mine-

I too have 26 guage 3 foot wide panels with a 10/12 pitch. I also did not exit the roof near the peak. I used a pipe boot. It was cheap, simple and has not given me any trouble. I used a regular boot (not high temp) since it is double walled pipe. Had a chimney fire the first year due to the constant burning of green wood and still have not had a problem. Keep in mind it is better to exit the roof through a rib rather than between ribs. The boot can fit snugly over a rib and allow water to flow around each side rather than being between ribs and allow water to collect. When water collects or stands leaks occur. I would attach a pic but I am deployed right now. Pipebootxpress is one of many places to buy boots.

A few months ago, I was in your exact situation. It isn't he easiest thing to figure out and something about a silicone boot was suggested to me. Problem is, I wanted to install it then and didn't know where to find one. My setup is similar to ddug's except that I had to install it about half way down the roof. My pitch is around a 5/12. The instructions mentioned installing the top half of the flashing UNDER the roofing and the lower half ABOVE the roofing. That is fine with shingles but not metal. I debated about installing it all over or under the roofing. Ended up cutting the hole about 4" larger in diameter than the pipe. Next, I laid the flashing over the hole and marked where the edges were. Since there is no way of bending the flashing to match the ridges in the roofing, I flattened the ridges that would be below the flashing. I put the flashing down with a generous amount of silicone caulking underneath and fastened it with plenty of screws. Next, I used a product from 84 Lumber called either Peel and Seal or Peel and Stick and overlapped the seams with it. It comes in a roll 6" wide, around 30' long, and roughly 1/8" thick. It is either white or silver on the top side and very sticky on the bottom, when you peel the protective tape from it. Depending on your outside temps, you may have to heat it slightly, but it will form to any shape necessary. This was 6 weeks ago, and no problems so far. I am sure there are better ways, but this was the cheapest and fastest route I could follow.

I have a steel roof with as well and I used selkirk's adjustable flashing and installed it just as you would with an asphalt roof - I made a cut perpendicular to the run of the roof that would accommodate the flashing sliding under and up, and I cut out enough of the steel below that cut to allow the chimney to pass through so it is T - shaped with the top being just a slit and the downward cut out a bit larger than the pipe. If the edge of the flashing running parallel to the ribs is going to just run on a rib trim it down so it will sit on the flat instead. If the bottom edge of the flashing will be centered on a rib where it runs over the roof (after the chimney cut out) check with your roofing manufacturer to see if they have gasket material or configure something yourself. My roofing manufacturer sells a rubberized gasket. I caulked with silicone and fastened with gasketed roofing screws. This is my second install this way and I haven't had a leak in the six years it's been up, nor at my camp where we installed 24 years ago and we get plenty snow on the roof. My wife had a reputable roofing crew install the same flashing kit at her family camp and they did it the same way. No leaks there either.

Is this a standing seam metal roof or corrugated w/ the fasteners exposed?

I just did a install like that on my small cabin. I went to pipeboot express and got there install kit with the boot. The sealer that comes with the kit is great, very sticky and flexible when cured (about 24 hrs). The boot is the grey epdm as per the manufacture of the triple wall chimney that I used. Mine sticks up about 8 feet above the opening so I braced it with some conduit that someone from this site suggested. Hope this helps and becareful on that roof.

Either triple wall or double will work just fine as long as they are class a rated. I used triple wall because a friend gave me some for free. As for the brace I used the band from an old chimney cap attached it to chimney about half way up and then attached 2 pieces of conduit to the band and then to the roof for support. I will try to post pictures later when I get home or you can pm me. Hope this helps.