DIY Custom Chimney Cap


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Old 05-19-15, 07:23 AM
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DIY Custom Chimney Cap

I am getting ready to replace a chimney cap. I am making this myself of galvanized steel. I have 28 guage steel for the top and bottom and will use hardware cloth to create the sides. This is a triple wall chimney, with the center being about 9 inches wide. The chimney/storm collar is 18" across and my chimney cap will be about 21" across.
You can see the basic design below- along with some colored points for my questions.

At eight points around the cap will be steel struts. They will be bolted at the top and bottom. The struts will go inside the mesh, thereby holding the mesh in place as well as supporting the top. On two sides with be crossbucking to keep the structure from helixing.

On the drawing, you can see red dots which indicate the bolts which will hold the struts and mesh in place. I am considering adding extra bolts and washers (on the inside) to strengthen the hold of the mesh to the top and bottom (these are the blue dots)

Now, comes the questions.
Are the extra bolts & washers even necessary?
Are they too little? Should I really be putting in 8 more struts or crossbucking?
 
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Old 05-19-15, 09:42 AM
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28 gauge seems awfully thin for a chimney cap. It sounds more appropriate for HVAC duct. Most material that thin is electro plated rather thin. It might be OK in a protected location like HVAC duct but exposed to the heat and elements it may rust rather quickly.

As for your question. I don't think the strength of holding it together will be an issue. You could even probably do away with the struts altogether and rely on the hardware cloth to support the top cap. I'm more thinking that every cut, scratch and bolt hole is a spot where bare steel will be exposed and more prone to rusting so I'd try to minimize the fasteners.
 
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Old 05-19-15, 10:34 AM
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Thanks for the input. I had planned on very part being painted with rest preventative paint before it's assembled. I also plan on repainting it every few years to keep it good.

28 guage steel is sufficient to hold up to a foot of snow (checked on another forum for an engineer to give me that information.) so the supports are there to back that uip as well as to keep it together.

So, I'd also say by your notes that the extra bolts (blue dots) to hold the hardware cloth in place would be overkill?
 
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Old 05-19-15, 01:26 PM
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I would hire a professional

Well if it's triple wall that means it's air cooled,which means you need an air cooled cap. Putting a standard or "homemade" cap simply won't work . Not to mention 28 gauge isn't thick enough I would go 24. Also there is a code for screening . The screen has to have 5/8 of an inch slots to prevent soot or creosote blocking the screen .
 
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Old 05-19-15, 01:43 PM
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The cap will be attached to the storm collar and leave all sections of the triple wall clear for air flow. Thanks for the heads up on the mesh code, I'll make that change in the design right away.

Again, I was initially concerned about 28 gauge and checked with someone who said that 28 gauge should effectively hold a foot of snow on top and though we never get that much snow on the roof, it should be more than plenty. If I see any problems, I can add an internal bracket for additional support.

As for hiring a professional, the reason I'm doing this is that i didn't have the money to have one made. (a cap to fit 18" would cost a few hundred dollars....a few hundred more than I have.)
 
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Old 05-19-15, 01:52 PM
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Okay as long as you don't cover up the triple wall airways you should be okay so connecting it to the storm collar should be fine . Also I don't think that 28 gauge is necessarily weak but like the other poster mentioned the risk of rust is way greater and rust damage is more significant.
 
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Old 08-05-15, 12:31 PM
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Just had to stop back and thank everyone once again. The cap is finished and I thought I"d also show how it was made and how it came out.

Chimney Cap from Garbage Can Lids
 
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Old 08-05-15, 12:39 PM
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Great idea! I love projects where you walk through a hardware store and spot some mundane object that makes that light go on in your brain.

Thanks for the update!
 
 

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