Seeking help on new chimney pipe install

[MaybeErnie]

I'm about midway through the planning and construction for installing a new woodstove, flue, and chimney. This is a 2-story house with the stove on the 1st floor, a support box in the ceiling above the stove, and 6" Duratech chimney pipe running from the box through a small upstairs storage closet (about 5' high from floor to roof) and out the roof. No attic above. I will build a chase around the chimney pipe in the closet, adhering to the required 2" clearance around the pipe. We're in Montana.

Because of the location of the rafters and a problematic roof design above (intersecting rooflines contributing to a snow melt issue), I can't run the chimney straight up from the support box and out the roof and will need a pair of 15-degree elbows in the storage closet. My plan is to put the chimney as close as possible to a rafter (8" Duratech pipe + 2" clearance on all sides = 12" hole through roof sheathing). There will be about 5' of chimney above the roof, so the total run will be about 5' of connector pipe, 5' of chimney pipe in the closet (between the 2 elbows) and 5' chimney pipe above the roof.

I was wondering if anyone would care to take a quick look at the images to see if anything jumps out at you. The images are all taken in the closet area (no chase yet) showing the support box framing in the floor, and the planned location of the pipe above (the cardboard cutout stuck to the roof). One thing I'm wondering about is whether the stipulated 2" clearance is really adequate and safe for the chimney. I do need to keep it as far to that side as possible to avoid problems on the roof so I'm hoping that the 12" hole will suffice.

Alternatively, I did consider going out through the wall in the closet area, but from my reading here, that introduces a number of problems (additional, more severe angles to bypass the soffit, draft issues from exposure to outside temps, required bracing, and other). However, I'm open to your sage advice! TIA!

 

[begreen]

There will need to be a firestop as it passes through the floor. That will help maintain the proper 2" clearance.

 

[MaybeErnie]

I was going to use an oversized, 24" DuraTech support box so that it will span the full 10" joist depth plus extend above the floor. Is that an OK substitute for the firestop?

Edit: I should add that I'll have a 12-16" section of pipe as the 1st chimney section (from the support box connection up to the lower elbow). Because that will sit in the center of the support box and extend all the way through the floor, I'll have the 2" clearance all around.

 

[begreen]

Yes, that will work.

 

[stovelark]

Looks good, you have thought it through well. Good luck with the project.