What dense Hudson County housing does to a chimney
A chimney in Union City lives a hard life that has little to do with how often anyone lights a fire. The masonry stands fully exposed on the roofline of a rowhome, taking the full swing of a Hudson County year, the wet heat of a river-valley summer, the wind and rain that come up off the water, and then the repeated freeze and thaw of winter on the Palisades. Brick and mortar drink water in during a wet stretch, and when that trapped water freezes it expands and works the masonry loose from the inside. On a tall, narrow rowhome stack, where the chimney often rises well above a flat or low-slope roof to clear the parapet, that exposure is even greater, and the crown at the very top is usually the first thing to surrender.
The burning season layers on a second and entirely different kind of wear. Every wood fire leaves creosote on the inside of the flue, a tarry, combustible film that builds in layers and narrows the path the smoke has to climb. In a building where flues are long, run cold up an exterior party wall, and may be shared or stacked, that buildup and the draft problems it causes can be harder to read than in a freestanding suburban house. Water working down from the crown and creosote building up from the firebox attack the chimney from opposite ends at once, which is exactly why a Union City flue needs looking at on a schedule rather than only after smoke has already filled a room.