If you look up the definition of "zero tolerance" in the Urban Dictionary, you'll see why I abhor this type of chimney. Don't look up abhor please. I have little tolerance for these unforgiving structures.
A zero tolerance chimney is a stick or frame construction that is used to box in a large metal chimney flue.
At the top there must be a cap, collar, and chimney cap. It's like the base on a hot water or furnace flue set up. The cap turns up the base of the flue and needs to be caulked with a metal caulk or soldered. If the cap, which is not over a solid surface, is not properly braced, it can sag, and water can work its way in.
The framing needs to be waterproofed with some sort of water barrier like felt or Tyvek. I prefer GreenGuard but that is another storey.
Then the plywood structure with waterproofing needs to be clad. Here is the rub. This is where you can die or, at a minimum, be crushed and maimed by falling masonry. The plywood framing and waterproofing need to be clad with something.
If the cheapest cladding is used, wood or hard board, you are in luck All these need is periodic painting.
Many years ago, I encountered chimneys in Valley Ranch and Hackberry Creek, as well as large parts of Las Colinas and Carrollton, with zero tolerance chimneys that were either four sides Masonite or three sides masonry and one side Masonite. I thought the builder was being cheap. Nobody knew the back side had siding and when the house was painted or sided with vinyl, aluminum or steel, the back side of the chimney was neglected. When I showed up, the back side was potato chips at best.
Then came the four sided brick zero tolerance chimney. I didn't know what it was called but I did know that the mortar joints were braking when the stick framed chimney swayed in the wing. We would seal the mortar joints and then water seal the chimney.
when the back side had Masonite, the 1x4 trim where the siding met the brick on the sides was pulled loose. When vinyl or other siding was installed over the wood like covering, the warping and gaps allowed wind driven rain to enter.
Then came the catastrophic four sided masonry zero tolerance chimney. You see, the normal chimney has masonry all the way from the top to the bottom and vise versa. The zero tolerance one has no such ankle bone to leg bone to hip bone support. The tremendous weight of the masonry, if just on the one side over the home that has masonry on the three sides of the exterior mounted chimney can cause the chimney to list and fall over.
Usually, when the zero type, and not a WWII Japanese flying chimney bomb, has masonry on four sides and the chimney is located within the confines of the home and not on an exterior wall, the heavy masonry clad zero is supported by steel post. The three sided outside wall type that should have wood like or vinyl siding type surfaces on the interior wall but has masonry instead, can be a serious problem. For many years the municipalities of Irving, Colleyville, Southlake, Trophy Club, Flower Mound, and anywhere large amounts of homes were being built in the 1980's and 1990's, allowed zero tolerance chimneys to be built with masonry on all sides, including the inside wall, without steel reinforcement bracing.
These chimneys listed, fell over, and did massive damage. Many insurance companies have adjusted this "Leaning Tower of Pisa" effect as wind damage. It might be but the origin is ignorance.
If you start on the ground with brick or stone and continue all the way up, you have something to support the weight. If you build a wood structure and put masonry on top of it, you or succeeding generations will pay.
These swaying masonry structures also crack. Mortar is not very pliable and before the tumble they will leak and crumble.
These cheap builders of the late 20th Century and beyond build these fake structures like zero tolerance chimneys and EFIS siding, leave property owners under the impression that they have masonry or stucco exteriors when they have cardboard and plastic trash.
There is no way I can explain to you how bad these systems are and how screwed you are if you have one of these products or structures on your home. We roofers get blamed for what these jerk off sociopath builders puts on your home that fails and allows water in just before they crash and hurt you. You might think it is your roof leaking but it not.
If you buy a home in the Dallas Fort Worth area, the roof is not the only concern above the ceiling. These trash chimneys and siding systems that achieve the absolute minimum available by building standard codes, can really cause you a lot of money and grief.
Just look at the word:zero tolerance. That should be enough.
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