What can cause a chimney to lean when it projects above the roof?

A chimney may lean when it projects above the roof due to deteriorated mortar joints. Over time, the mortar that holds the bricks or blocks of the chimney together can break down due to various factors such as weather exposure, moisture infiltration, and thermal expansion and contraction. When these joints are compromised, the structural integrity of the chimney can be negatively affected, leading to leaning. This deterioration reduces the overall stability of the chimney, especially when it is subjected to wind forces or the weight of the chimney itself.

While other factors like poor construction, excessive weight from the roof, and improper flashing installation can contribute to chimney issues, the specific process of leaning is closely tied to the deterioration of the mortar joints. This highlights the importance of regular inspection and maintenance of chimney structures to ensure that mortar joints remain intact and effective in providing support.