Class A chimney wiggle room?

[bumblebeetuna96]

I went in the attic to plan my install for the woodstove. Im running a double wall class a through the second floor, then the attic and into the roof. Using a plumb bob the clearance for the radiation framing and the roof is a little over a half inch off from giving me my 2 inch clearance. Is it reasonable to assume theres enough flex to be able to skew the chimney 1/2" - 3/4" over 5'? If not am I better off framing another plumbers box or doing an offset in the attic?

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[webby3650]

You can gain 1/2” in a 5’ length. Remember the clearance is 2” from the pipe, not the radiation shield.

 

[Ludlow]

The smoke wont care if it is 1/2" out of plumb, but like said, you only need 2" from the pipe not the shield.

 

[Highbeam]

I hate crooked chimneys sticking out of the roof.

 

[Ludlow]

The casual observer probably wont notice a half inch. If I put it in I would notice though.

 

[Sawset]

Where is the guy with a pretzle shaped chimney. I bet his is out by 3/4in5.

 

[bumblebeetuna96]

I know its going to bother me, but Ive never worked with the pipe or the radiation sheilds ect. Is there flex? I don't want to have to bend anything and I'm sure the inspector wont be happy. A 1/2" isnt much but I was hoping for a clean install.

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[webby3650]

I know its going to bother me, but Ive never worked with the pipe or the radiation sheilds ect. Is there flex? I don't want to have to bend anything and I'm sure the inspector wont be happy. A 1/2" isnt much but I was hoping for a clean install.

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Well then elbow it. The offset is usually around 3” depending on the brand.

 

[Rearscreen]

If I am understanding this correctly, you are too close to the roof rafter to come out the roof plumb by 1/2 inch to keep the proper clearance. If this were the case in my house, in an open attic situation, I'd sister on a 2 x (whatever your rafter width is) to the opposite side of where the pipe is, then cut out a small section of the existing rafter. If, for instance your pipe landed farther into the rafter, a box of course would be needed.

 

[EatenByLimestone]

I'd sister a new 2x on and shave the original 1/2" too.

 

[Sawset]

If I am understanding this correctly, you are too close to the roof rafter to come out the roof plumb by 1/2 inch to keep the proper clearance. If this were the case in my house, in an open attic situation, I'd sister on a 2 x (whatever your rafter width is) to the opposite side of where the pipe is, then cut out a small section of the existing rafter. If, for instance your pipe landed farther into the rafter, a box of course would be needed.

This would be what I did on my setup. A set of 45s would not have worked. They say never to cut into a truss - however - I needed an inch, a sheet of 3/4 ply, glued and screwed permanently to the side of the entire portion of the truss provided a high margin of safety. And more strength than the "optimized for material use" truss alone could provide. Fastened securely, snip the truss, run the chimney, use a caulk tube at 2" dia as a gauge to check clearances.

 

[Ludlow]

There is no flex. When locked together that stuff does not bend at all.

 

[maple1]

There is no flex. When locked together that stuff does not bend at all.

That's what I was also thinking.

 

[bumblebeetuna96]

I'm getting permits for my install and I'm not sure how the town will feel about the "plumbers box" I'm doing in the floor. I guess if they're okay with the floor, they should be okay with the ceiling. The pic is how I plan to do the floor. If I use two 15 degree offsets in the attic, the chart says I'll get 2 inches of offset. Im already offsettting with a set of 45s with the stove pipe in the living room and don't know how much a second offset will affect performance.

 

[Highbeam]

I needed about a half inch too so I actually slid the ceiling support box away from the ceiling joist and used a chunk of 1/2” plywood as a shim to fill the gap. The trim ring covered the oversized hole.

The rigid class a has no flex but you can certainly lean the whole thing over by flexing the threads at the bottom.

I’m sure there is a little slop in every class a joint so that if you had 100 little 1 foot sections you could try and snake it but a proper, plumb, level job would look best and be proper.

 

[bumblebeetuna96]

I wish they made reduced clearance parts for 8". The boxes and sheilds need 14.25 inch frames. Its not easy to line up two ceilings and a roof perfectly with the 1/4 left over!

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[Sawset]

On the bottom view of your sketch, the outside floor joists may also need to be doubled.

 

[bumblebeetuna96]

On the bottom view of your sketch, the outside floor joists may also need to be doubled.

That would be tricky. Its a finished floor [emoji27]

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[begreen]

The casual observer probably wont notice a half inch. If I put it in I would notice though.

Depends on how much is sticking out of the roof. A 3/4" tilt at the roofline could become a couple inches at the chimney cap. That would be noticeable and would bug me.

If there is already an offset planned for the stove pipe what about moving the ceiling support into the next joist bay?

 

[maple1]

Depends on how much is sticking out of the roof. A 3/4" tilt at the roofline could become a couple inches at the chimney cap. That would be noticeable and would bug me.

Yes, but I don't think you can flex Class A like that? Pretty sure you can't mine - it screws/locks together, plus has locking bands over the joints. The whole chimney would need to tilt. So 3/4" at the roofline would be about the same at the cap, on say a 20' chimney.

 

[begreen]

Is it reasonable to assume theres enough flex to be able to skew the chimney 1/2" - 3/4" over 5'?

 

[maple1]

I guess it comes down to how tall it is and how much of that is above the roof. I was picturing one section above the roof. Which could be off.

 

[Ludlow]

Depends on how much is sticking out of the roof.

Indubitably.

 

[Highbeam]

I only have 8 feet of class A between ceiling support box and cap. When I'm on my roof I can easily wobble it around a couple of inches until it bonks into the cone of the roof flashing. This wobble is due to the loose threads at the ceiling support box, not at the joints in the class A.

Remember when you screw the class A into the ceiling box it's only like a quarter turn of thread engagement, and the threads are shallow. If your class A is further supported to the house above the ceiling support box then it might be less wiggly.

 

[WinterinWI]

I only have 8 feet of class A between ceiling support box and cap. When I'm on my roof I can easily wobble it around a couple of inches until it bonks into the cone of the roof flashing. This wobble is due to the loose threads at the ceiling support box, not at the joints in the class A.

Remember when you screw the class A into the ceiling box it's only like a quarter turn of thread engagement, and the threads are shallow. If your class A is further supported to the house above the ceiling support box then it might be less wiggly.

+1. Almost all the wiggle room comes from the support box, from that point on, the angle of the chimney is pretty locked in.