Hi I am looking for advise please. My cabin roof is corragated bituminous sheets (onduline) and I am wanting to put in a 4" flue for a wood burner I'm making. I have looked at some rubbery sink plunger like things but am concerned about the heat on the sheets. I could run the flue up the outside of the cabin but it seems a shame to loose the heat. I have seen the rubber funnel things on a yurt canvas but this is obviously flat and less susceptible to heat damage, distortion or degradation. The metal skirt/flange is bigger too. Am I better off replacing say a 12" square with a flue section? Keeping it flat too as moulding something to the same profile as the roof seems a big ask for a sealed edge.
I'll only be burning wood in a small gas cylinder stove but the cabin is quite low sided so stove to roof is only about 4'.
Thanks for any thoughts or suggestions.