How much should masonry chimneys extend above any portion of a building within 10 horizontal feet?

Masonry chimneys should extend at least 2 feet above any portion of a building that is within 10 horizontal feet. This requirement is primarily based on safety and performance standards concerning the proper drafting of flue gases. When a chimney extends higher than the roofline, it helps prevent downdrafts that can cause smoke and gases to be pulled back into the building.

Additionally, having the chimney at this height reduces the likelihood of issues caused by wind turbulence that can affect the efficient operation of the chimney, as it maintains proper airflow and ventilation. The 2-foot extension also aligns with common building codes and best practices for chimney construction.

In contrast, the other height specifications are less effective in achieving the necessary clearance for proper chimney function, which is why they do not meet the required standards established for masonry chimney installations.