Wood stove chimney flashing
Installing wood stove chimney to go through cathedral ceiling with 12/12 pitch. This is new construction. Roofing material will be galvalume R panel. On the roof, what is the recommended layering system to prevent moisture from entering at the chimney penetration? I have seen metal roof with the flexible high temp boots on top sealed with silicone, and I have seen 12/12 metal roof flashing adhered by sealant directly to the roof sheathing with the roof panels cut around the flashing and sealed , and a combination of many other ways. What is the best practice for new construction for flashing a 6″ wood stove chimney on a 12/12 pitch with galvalume R panel?
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Replies
Scott,
The best practice is to purchase the flashing kit sold by the chimney manufacturer and to follow the installation instructions provided with the flashing kit.
There really isn't any choice here. Metal chimneys are proprietary systems. You have to use the accessories provided by your chosen chimney manufacturer.
Andrew,
Thanks for the pics and the detail. I have a couple of questions. Since I am venting under the sheathing, instead of a top vent cold roof, I don't think I would have room for the silicone boot. Would you agree? And, did you have the raised flashing pan custom made and how did you spec that to the fabrication shop? My R panel has 12" spacing and 1 1/4" tall ribs. I have looked at the flashing pan made by ICC but have read that it doesn't work well with the taller ribs.
I have an R panel 12/12 pitch roof with chimney. I feel your pain; it's tough to find definitive advice for this scenario. I will tell you what we did, with some bonus info because we have a SIP roof with cold roof above.
Our Excel chimney goes up through a square radiation shield for a cathedral ceiling (ERSC). The radiation shield runs through both the SIP and the cold roof; I have attached a quick picture of it. It's hard to see in the picture, but we had an additional metal ring machined to help seal the bottom of the radiation shield.
The original plan was to terminate the top of the radiation shield with a Dektite silicone boot. Unfortunately, on a 12/12 roof, the circle of a round flue pipe turns into an oval, and that doesn't scribe to a stepped rubber boot. We had to use the R panel roofing and caulk to terminate the top.
At the R panel roof level we have a large flashing pan. It's modeled after the EF series that Excel offers, except we had to raise its height because of the high ribs on the R panels. Our roof penetration location was dictated by the need to avoid a SIP spline. Unfortunately that was a less than optimal location for R panel ribs, so that flashing pan ended up pretty wide. Pix attached.
Scott, we purchased the Excel flashing pan and realized it wouldn't work (due to the R panel rib depth and spacings), so we had it as a model for the tinsmith. Then our dealer was kind enough to take it back.
As I looked through my pictures last night it suddenly dawned on me that the Dektite boot had to go back too, sorry for the faulty memory. The boot wasn't flexible enough to bend over enough for a 12/12 roof, and you couldn't cut an oval in it either due its stepped graduations. Sort of hard to explain without having the unit in front of you...it's one of those "well that is not going to work" moments.
I have attached some more zoomed in / cropped images to show the radiation shield penetration location versus SIP panel, extra sealing ring that we had machined for us, and the depth of an R panel rib versus the chimney.