What might cause a brick chimney on an older property to curve above the roof line?

The phenomenon of a brick chimney curving above the roof line can be attributed to the expansion of mortar. Over time, mortar can undergo changes due to temperature fluctuations, moisture absorption, and drying. As it expands and contracts with these changes, the structural integrity of the chimney can be compromised. This expansion can lead to tension on the brickwork, causing the chimney to bow or curve away from its original straight alignment.

The other factors mentioned play a role in chimney issues, but they do not directly cause the curving effect. Settlement of the chimney footing may lead to vertical displacement or cracking, rather than curve. The absence of a cricket flashing could contribute to water damage or leaks but wouldn’t directly cause a curve in the structure. Finally, while a lack of a rain cap can lead to deterioration from moisture and debris buildup within the chimney, it would not result in a physical bending of the chimney structure itself. Thus, the expansion of mortar is the primary cause of the curving effect observed in an older brick chimney.