Masonry Chimney - No Ties Required per IRC? what??

[Jerehmy]

We are doing an insurance claim on this masonry chimney. Its 18"x18" with 1.375" wire lath and plaster, 3-5/8" brick, and an 8"x8" flue. It's 13'-2" to the roof line and extends beyond the roof line 4'-4" for a total height of 17'-6".

The thing fell over. It was leaning for a while, the mortar where the steel ties deteriorated so it was just cantilevered up from the ground.

Here's the issue. I did a wind calculation on it. I took the portion above the roof and went to ASCE Section 30.11 which tells me to go to ASCE section 29.5.1. OK. For the portion below the roof line, I used ASCE wall wind loads.

I calculated my overturning. Something like 6.3kip*ft. Calculate my restoring moment, get 2.1kip*ft. Makes sense.

I go to the IRC 2012 and go to the masonry chimney section. R1003.3 states: "... In Seismic Design Category A, B, or C, reinforcement and seismic anchorage is not required."

I'm in seismic design category A. So no ties required. It doesn't even make any reference to wind or any other reference requiring any ties back to the house. What the hay? It doesn't give any maximum height or anything. Just has to extend a minimum of 3ft beyond the roof line.

Am I missing something here? How can they not require ties? What about wind?

 

[BAretired]

The chimney should be laterally braced by the structure at roof level. Otherwise, it is a very long cantilever.

BA

 

[Jerehmy]

I'm in full agreement on that.

My problem is, I went to the IRC looking for a section that said something like "you need lateral ties every ___ ft vertically". I wanted something to go with my analysis that showed ties are required per the IRC.

The IRC said the total opposite and I looked through the whole masonry chimney section. It said I only need ties when I'm in a seismic zone. Never referenced ties again and never referenced any wind concerns.

 

[dicksewerrat]

Was the chimney part of the wall of the house? I've seen many chimneys with no ties to the bldg. The brickwork was part of the exterior wall and the roof was tight to the chimney with some flashing to separate the brick from the flammables.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Jerehmy]

No. A masonry chimney should have ties, the loads just don't calculate out. I don't understand why the IRC doesn't require any ties except for high seismic regions. There are also no height limitations.

In my area right now, I can draw up plans that aren't stamped and have a two-story residential with a 24ft masonry chimney that has NO TIES to the house and no one would say anything. It's not required per the IRC so what's a building inspector going to say? Nothing.

I'm confused to say the least.

 

[XR250]

I have never seen them, but we are not in a high seismic area. My plans always just say, "Chimney per code"