No reason I could not run a rigid pipe above the chimney a few more feet; it might take some guy-wires, which can be done. The drawback is that, at the chimney's present height, I can presently clean the to-be-installed-stovepipe by standing on the roof and inserting a brush into a pipe that rises a convenient five feet from the roof. The roof is multi-layered, but the top layer is foam with an elastomeric coating on top - in a word, delicate. So increasing the height of the stovepipe would mean every time the stovepipe needs a swabbing, someone would have to haul a stepladder up to the roof, and a piece of plywood to protect the roof surface from the ladder. The slope is gentle, so I don't think the slope makes the stepladder dangerous, but I am a bold guy. Now, I'd be willing to do that once or twice a year. But to make a long story short, it is possible that, in years to come, other people, not myself, who are less enthusiastic about home care in general, and not wood stove conneseurs in particular, might be the ones residing here for periods of time. And they may find this cleaning procedure with prophylactic plywood and balancing on uneven step ladders on a roof to be something they'd rather put off or delegate to other, even less competent persons. And so, if I can avoid that set up, I sure would like to. If I cannot avoid it, it will be one more PITA I will have to work around.