In the process of residing a clients house, I have discovered severe sheathing and framing damage just beneath the chimney cap, at least on one side that was striped of siding on Friday. House is a late 1970′ contemporary with a wood framed flue chase. Cap is about 3’x4′, about 3″ thick at the edges, and appears to be in very good condition, although it was a disaster from a framing perspective (no kerf underneath, minimal overhang, etc.). I’m wondering if the framing/sheathing can be repaired with the cap in place. Any ideas on how to determine if the cap is adequately supported? It appears to have been poured tight to the flues. Working on this 12 pitch roof is creepy enough, the prospect of a 600 pound chunk of concrete dropping onto my chicken ladder is starting to make me queasy.
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I have discovered severe sheathing and framing damage just beneath the chimney cap,
In a well designed chimney/flue system, the chimney cap/crown should be 2.5 -3 feet through the roof! The Canadian code has a minumum of what we call the 3-2-10 rule- 3 feet height above the roof and 2 feet higher than any roof (or wind obstruction) within a 10 foot diameter of the chimney.This chimney sounds like it was not built right if framing/sheathing material is just beneath the cap.
I was confused until I got to the part about it being a concrete cap.
wood chases like that should be capped with a top custom made from the sheet metal shop. No concrete is water tight
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Me too, I was thinking, it's sheet metal so how it is three inches thick? Why on earth would someone choose to lug a concrete cap up a steep roof like that. Unfortunately, getting it down safely will be at least that hard.
I'm almost certain that after the chase was framed and sheathed (it's the highest point on the house), the cap was simply poured in place around the three flues. It appears that over time, water has rolled off the top of the masonry cap, down the edges, and then along the underside of the cap until it hit the framing. Wish I had taken some "before" photos showing the original vertical siding (4" v-match cedar), the sheathing is coming off tomorrow. Should be an interesting day.
Sounds like they needed a sheet metal cap under that concrete, same as they'd need without the concrete. If you're replacing the siding you'll need to do something to prevent the same damage from happening in the future. I'd be tempted to chop up the concrete and toss it off the roof in chunks, then replace with metal.
I suppose you could attempt to waterproof the surface of the concrete, and flash underneath it somehow so water cannot roll off the edge and underneath, but neither one sounds like a great solution.
What would the reformed roofer from Isleboro do?
i'd get the demo hammer out and make some good fill for the potholes in my driveway out of that current cap. Then I would rebuild the chimney chase. Plywood the top and bituthene it, with a trim piece at edge to make sure the water is shedding away from the wood parts.Then I'd call the sheet metal guy.
Actually, I would fax him a detailed drawing of what the cap will be and save him a trip on the ferry.
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Me too. We have a sheet metal guy here who doesn't have to ride the ferry. I can usually find him in three or four tries. To a west-coaster there's no way a heavy concrete cap makes sense on top of the chimney. A good shake might bring it down into the living room while we're playing chess or something.