My issue with that situation was that with a cathedral ceiling (essentially - the floor of the attic is not vapour sealed from the rest of the cabin), I essentially had a hole in my roof where the stovepipe stuck through!
Thinking myself somewhat clever, I packed the upper roof cone full of stone wool insulation and then sealed it all up with loads of foil tape.
The next time I was talking with the good fellows at Thunder Bay Fireplaces though, I was warned that this was not appropriate, and it was suggested to even be a fire hazard. I'm not certain how though; I'd love to have someone enlighten me...
I began this project last spring, but as the weather warmed up, it moved from a priority to a "mañana" situation.
Of course, it hung over my head all summer, and with nothing particularly planned for a recent day, I steeled myself with a warm mug of tea, and slipped into my overalls. I promised myself to just cut "one board" and then I could quit if it was too annoying or discouraging. Of course, one board led to another and I pretty much would have finished the entire deal if I hadn't run out of expanding spray foam.
I put in sheets of closed cell foam on the floor and walls of the attic "room" around the stovepipe, and then sealed it with spray foam. Then I piled more stone wool insulation on top of the floors until it was about four to six inches below the "no insulation above this line" mark on the stovepipe thimble.
|Once more into the breech after six months of avoidance.|
|Hard to make out - this is a small crevice packed solid with a mass of dead flies. Not the way I'd want to go!|
|Here's the final wall with most of the plywood installed. I opted not to bother with a stud for extra support in the centre, as it's simply a barrier, and not at all structural.|
|The final wall in position.|
|I packed the outside top edge of the walls with stone wool to support the spray foam on the inside. Note the transition to the latex foam at the top edge of the wall - it allowed me to install it with the can held upright in this tight space.|
|A view through the peephole. Things look messy but functional. I removed all the stone wool from the cavity above just before sealing in the stovepipe.|
|And on the floor, a deep covering of stone wool. Just beneath the collar, you can see the red tape marking the maxium height of insulation.|
|Ugh, the latex foam is clearly past its best before date.|