Anybody have a good idea about how to flash around a metal stove pipe for a coal forge that passes through a corrugated, galvanized metal roof?  I am re-purposing a horse shed as a blacksmith shop.  I would prefer to go straight up thru the roof rather than bend out thru the wall and up.  We don't have a lot of rain here in central Wyoming, but still it would be a good idea to keep this in check.

Have you cut the hole in the roof yet? If not I'd suggest going out the wall using a side draft instead. If you insist on going through the roof you might want to look for a boot to fit the pipe. Of course it depends on the size of the pipe if they even have one that'll fit it.

If you want to go through the roof ... you have to solve two problems. One is sealing around the pipe for rainwater and two, shielding the heat from burning your roof structure. 

For sealing around the flue, you can buy purposely made flashing for the profile of your roof. Since you need a minimum of 8", your last section of flue through the roof needs to be double and the external section 10" so the flashing has to be for 10". 

Make sure your flue goes through the roof in the center between the rafters without touching any. Make a bracket to hold up both the external and internal pipe out of L section and screw to the rafters. 

The cowl for your flue needs to be 10" and the internal 8" will have to end at the same level.

If you want to have a 10" flue then of course you need your heat shield to be 12"

 

Marc1 is of course assuming that you have wooden rafters in your roof.  My shop's roof has metal trusses, metal purlins and a metal roof held on by SDST metal screws and so does not have the issue with mandatory offset spacing of a chimney.

How is your roof constructed, you didn't say?  If this is an insured structure there will be a building code you need to meet; generally set up for wood stoves and furnaces though a forge chimney will NOT get nearly so hot in use.

Check with your local building supply company as there is probably a specifically made boot that will key into your corrugations and some good silicone caulk and some screws and you are done.

Its an uninsulated pole barn with 2x6 rafters and 2x4 purlins at 24"o/c each way.  Its just an old 10x16 shed.  The metal roof panels are nailed down to the purlins.  My flue would be centered between rafters and purlins, and the pipe would contact only the metal roof.  No luck finding a manufactured pipe flashing or boot. The corrugations are about an inch deep and 2 inches wide.   Maybe I can fabricate something. Thanks all.

 check out any place that sells the metal roofing, they should be able to get you a boot that will fit the profile of your metal panels

 

A lead flashing will get you close and then roof dope, mastic or "good" silicone.  Not sure about your area I used to order large sizes while in west Texas.  The guys would take a worm clamp and shrink to neck to fit.  If your careful you don't need the storm collar.  

I bought a turbine vent that came with its own boot/flashing.  I ran the stack through the roof and put the turbine on top of that.  No leaks.  It's 12" pipe centered between the 2X4 purlins.  At the height where the pipe goes through the roof, the temp seldom exceeds 100 degrees F.

 

Don't know if you did it yet but I put a 8" Chimenea pipe thru a corrugated metal roof almost 20 years ago and it is not leaking yet. I simply got the flashing then used a tube of GE Silicone on the uphill side and pressed it down. Don't try to seal the downhill side or it could trap water in and leak. I've had some roaring fires in that Chimenea over the years and the pipe immediately above it has gotten sizzling hot but the silicone is still holding. The silicone also is rubberized so it gives for expansion instead of cracking like plastic roof cement.

I have not done it yet, but I had actually decided to do exactly as you said bigb.  I bought some sealant that is good for 500F.  Now if winter will go away for a while I will finish my shop!  Thanks

Mate I will have the same issue as you, and will be putting a sheet metal flue through the corrugated iron roof. My daughters partner is a roof leader, and he will flash the flue   off with sheet lead and mastic.

Sorry for the slow follow-up.

I cut a neat, tight fitting hole through the corrugated metal using a jig saw and metal cutting blade, then sealed the gap with hi-temp stove sealant.  It fits the pipe tight enough there isn’t any noticeable wiggle in the wind.  It doesn’t leak for now.  I suppose it will eventually and I’ll decide whether to get more elaborate or just add some sealant.  We don’t get a lot of rain here anyway.  The roof only runs about 5 feet above the pipe so the amount of water isn’t much.

Thanks!