Originally published in the June 2016 issue of Sweeping Magazine
Question: If a masonry chimney does not meet current minimum height requirements, do I have to raise the height if I am relining it with a listed liner system?
by Mike Segerstrom
It is not uncommon to have a chimney that needs to be relined, that is also not the minimum required height. Chimney height requirements have been the same for many decades. The standard for pitched roofs has been 3 feet above the roof penetration on its shortest side, and 2 feet higher than any portion of the building structure within 10 feet.
There are a variety of methods to accomplish this. Here we will review several of the most common. The first we will look at is adding masonry to the existing structure. Often this is very straightforward. Find matching brick and add the necessary amount. Older brick work and certain mortar joint colors and styles may be difficult to match. Block work may be added to block chimneys, or added to brick chimneys if the exterior will be finished with a stone veneer or stucco type finish. Raising the height of older natural stone chimneys can prove to be the most challenging. In some cases, adding brick work or masonry finished with stucco at the top of a stone chimney can create a unique look that appeals to the homeowner.
At times there will be budget limitations or other circumstances like aged, slate or wood roofing materials that may make adding masonry a costly, difficult or unfeasible option to consider. In addition to adding masonry, we do have approved metal pipe options. Several Class A chimney manufacturers that also manufacturer listed liner systems offer a transition plate to connect the two. This plate connects to the top of the listed liner and is secured to the chimney structure. We can then attach the necessary length of Class A chimney pipe to this plate. When using this option, we must follow the manufacturer's installation instructions for attaching the transition plate to the chimney, and for adding additional pipe support if the added section of class is over a certain length. This is also a cost-effective option if the top of the chimney needs to be rebuilt. It allows us to take the chimney down to solid brick work, and replace it with Class A. We can even take the chimney down below the roof, and then install a metal flashing where the Class A penetrates the roof. Certain Class A pipe manufacturers also offer decorative powder coating, or this may be done locally. This can help blend the appearance of the pipe with the surrounding roof or home.
Another option to address insufficient height is to use UL listed B vent or L vent in conjunction with chimney liner. Certain manufacturers of aluminum and stainless steel liner also manufacturer B vent and/or L vent. B vent and L vent along with aluminum liners don't have the same life expectancy or warranties as stainless steel liners and Class A chimney pipe, but do give us an option to properly reline a chimney and address chimney height. When considering this option, we must verify with the manufacturers that this application is permitted. They will have listed components to make the transition from flexible liner to B vent or L vent, and will have requirements for additional pipe support if it extends a certain height out of the chimney. Different brands of B vent and L vent are also listed as chimney liner. This allows us to install the piping in the entire chimney without the need for flexible liner.
At times we may find ourselves in a position where the AHJ indicates that the chimney height does not need to be raised. They may give us approval to reline a chimney that does not meet current height requirements. The AHJ may not fully understand height requirements, or the requirements of the listed products we use. If we find ourselves in this situation, we should consider the facts carefully. The listed liner system will specify that the chimney meets current height requirements. If we are connecting our liner to a new listed wood stove for example, the wood stove manufacturer will also have current chimney height requirements. As the installers, we are responsible for the installation, and may be liable for an issue that results from improper chimney height. Relining a chimney that is too short for a woodstove may create performance and/or safety issues that the AHJ does not understand.
We should use this as a friendly opportunity to help educate them. It might not always be easy but a little bit of effort and patience can go a long way. This will allow us to do proper installations without conflict with the building official, and to maintain the listings and warranties of the products we use.