While you may never need to know the 3-2-10 rule in order to build yourself a chimney, knowing why is exists is still interesting. Remember the 3-2-10 rule is the minimum height requirement.

It is widely known that masonry chimneys are required to meet the 3-2-10 rule. This rule means that they must extend 3 feet above the roof penetration on the shortest side, and the top of the chimney must be 2 feet higher than any portion of the building structure within 10 feet. This height requirement for masonry chimneys penetrating or adjacent to pitched roofs has been around for many decades. But why is this? I personally have been working on chimneys since 1997, and have been actively involved in the industry and with industry professionals for the past 10 years. I have asked this question many times, of many different folks in the industry. I have discovered that there is something of a divide in the reasoning behind the 3-2-10 rule.