Factory-built chimney lateral support

I will be replacing a factory-built chimney in a one-story ranch. The existing chimneys are held in place by combustibles (plywood at the top of the chase, sheetrock going from first floor to attic), so I can't just replace what's there. I need to know what the right way is. The new chimney will begin at the ceiling in the basement, go through the first floor in a dedicated chase, go through the attic unchased, and into a chase from the roof to air. I know that the chimney will be supported and anchored in place at the bottom by the chimney support going through the basement ceiling to the first floor. The chimney *might* be held in place laterally by brackets going up. I'm guessing it's held in place going from first floor to attic by the attic insulation shield.

What I can't figure out is what actually holds the chimney in place at the very top, right before the chimney goes through the chimney chase cover. As far as I can tell, the chimney chase cover itself must leave a standoff to the chimney, so it's not actually touching the chimney. Maybe I'm wrong. It would make sense to me that the chimney chase cover would also hold the chimney in place, but I think I read that the holes in the chimney chase cover must be 2" bigger than the chimney outside dimension.

Hope this question makes sense.

Ken Benson

So assume chimney stands 6' above rooftop. If it was unchased, it would have a 2-legged brace. But it's inside a chase, and no part of the chase actually touches the chimney because of the 2" clearance all around the chimney.

What braces it? It has to be braced somehow.

One of my chimneys will stand about 6' above rooftop, the other about 7'. Existing chimneys are braced between rafters (at least, that's the way they're done now; if there's a more correct way I would change the one I'm leaving). Existing chimneys are further braced by the plywood and shingle chimney chase cover that touches them. I will fix this, by replacing the chase cover with a stainless cover, but this will remove the lateral support that the (illegal and dangerous) plywood is providing now.

We've been using the oil burner chimney with this setup since we bought the house in October, but I'm adding a wood boiler and I don't feel safe the way it is.

Ken Benson

There is no "roof" inside the chase to attach a regular roof bracket to. It's just a rectangular hole into the attic (see picture in first post). I could close it up, and then cut round holes, but I don't think I need to.

What about an adjustable wall strap (see picture). I think these are meant for through-the-wall chimneys, but it seems like it would work. Is there anything against code or unsafe about this?

Ken Benson

BTW, I can see the utility of buying all stainless steel chimney (the galvanized-on-the-outside chimneys I have now on my roof are rotting on the outside, outside the chase). But what about non-pipe components that are never going to get wet, like the strap above? Selkirk sells the same thing in galvanized for about $20 less.

Ken Benson

Wood Heat Stoves said:

the strap is overkill.
the ceiling box supports the weight.
firestop at floor one ceiling level, and chaise top support side to side.

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That's what this is all about, though. The chase *doesn't* support anything other than itself.

The chimney must maintain 2" clearance to combustibles inside the chase (the entire chase is combustible), and the chase cover leaves 2" extra room all around. So the chimney is just blowing in the wind up there. I guess if it really blew hard it would run into the chase cover, but wouldn't it be better to strap it to the inside of the chase so it can't move at all?

Or am I missing something elemental? The only chase I've ever peeked inside is my own, and it's got chimney held in place only by plywood, which even I know is definitely wrong.

Ken Benson

Yagminas Masonry and Wood-heat said:

I'd cut the plywood chase top with 2" clearance and flange-fit the metal capping around the pre-fab chimney.

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I've been looking at made-to-order chimney chase covers like what you see at http://www.woodlanddirect.com/Chimney/Chase-Covers/Chimney-Chase-Covers. I've also been laboring under the delusion that there must be a gap between the pipe and the hole in the cover. I was wrong. I just called Woodland Direct and they said the hole is 1/4" bigger than what you tell them the external dimension of the pipe is.

So this solves my problem. The chimney chase cover keeps the chimney from moving side to side.

Thanks everyone.

Ken Benson

Wood Heat Stoves said:

the strap is overkill.

Click to expand...

Thanks, Dave

Leaving out the straps (two chimneys) saves me $108.

Ken Benson