Rules to build a fireplace chimney this rule is known as the 2-3-10 rule or the 10 foot / 2 foot rule, which states that the lower section of the chimney from the roof penetration point must be clear from the top termination point of the chimney by at least 3 feet.. Building code - masonry chimneys and masonry fireplace construction codes.. A masonry fireplace consists of a brick or stone firebox, a brick or stone chimney, and, more often than not, a wood mantel. it�s a lot easier learning how to build a fireplace like this in new.
