Chimney Pipe Penetration

[midrover170]

Hi all -

Recently installed my chimney pipe at the cabin. Cathedral ceiling, rafters 12" OC, reduced clearance (10.5") cathedral ceiling support box, 8" outer dia. DuraTech pipe.

At the penetration through roof, I cut the plywood back as close to the edges of the support box as possible. Maybe .5" inches shy of being flush. When I was getting the support brackets on the pipe, I needed to angle the pipe slightly toward one side to get it plumb. This was a little bit of a concern, because regardless of how you install 8" outer diameter DuraTech in a reduced clearance box, you're going to be less than 2" away from the combustible roof deck. This worried me, so I used some z-flashing to face all of the exposed roof deck, applied with high heat silicone. Now, no matter where the pipe sits, it's completely surrounded by a non-combustible material.

Does this seem OK to folks, even if the pipe was resting, or close to resting, on that z-flashing?

- D

 

[bholler]

No you need 1" from the outside of that pipe to any combustible material. while it is inside that box once it is past the box it goes back to 2"

 

[begreen]

The Z flashing does nothing to reduce clearances to combustibles which are right behind the flashing. The class A chimney pipe needs 2" clearance from the roof decking as it passes through the roof.

 

[midrover170]

Darn... Have a raging wildfire a mile away from the build and was hoping not to have any other issues.

So, if in my shoes, what would you do? Rip up the $100 silicone boot, try to save it, and cut out the opening bigger? Seems like the only option at this point.

The Z flashing does nothing to reduce clearances to combustibles which are right behind the flashing. The class A chimney pipe needs 2" clearance from the roof decking as it passes through the roof.

I suppose my only question is how the support box is any different in a reduced clearance application. It's made out of the same thin material as the z-flashing and there are rafters touching the outside wall.

 

[begreen]

Reasonable question to ask. The main difference is that it was tested safe for the reduced clearance. What I don't understand is why the cathedral ceiling support box was not brought up through the roof and why a silicone boot flashing was used? Is this a metal roof?

 

[midrover170]

Reasonable question to ask. The main difference is that it was tested safe for the reduced clearance. What I don't understand is why the cathedral ceiling support box was not brought up through the roof and why a silicone boot flashing was used? Is this a metal roof?

I had to get the support box installed early to be ready for drywall. Pipe/boot wasn't on site (hour from home, off-grid, etc.), so I cut it to the pitch of the roof and installed it flush like I've seen on here. This is a corrugated metal roof.

I just submitted a service request with a local mechanical contractor. Going to have them come up to make it right/safe and prepared to pay for it...

I'm running out of time and need to pick my battles from here.

 

[begreen]

I appreciate you dilemma. A picture or two here would be worth a lot to help see what you are seeing. Normally one would extend the cathedral box out of the roof and fold over the edges to make a flange, but metal roofs present their own challenges.

 

[midrover170]

I appreciate you dilemma. A picture or two here would be worth a lot to help see what you are seeing. Normally one would extend the cathedral box out of the roof and fold over the edges to make a flange, but metal roofs present their own challenges.

Guess that's part of the problem now, begreen: it's impossible to see now that the boot is on there. Sheetrook is up so hidden from below as well. This is about the best I have...

 

[bag of hammers]

Nice view - nice cabin too. Good luck with the chimney fixes. It'll be worth the extra effort in the end.

 

[begreen]

Yes, that looks nice. Unfortunately we are getting introduced after the installation is complete. The best we can do is suggest the correct way to install. The z metal may help, but there's no way we can know that for sure.