One of the most common reasons for the rain to leak into a chimney is physical damage or wear and tear to the chimney. The portion of your chimney that extends outside of your home faces near-constant exposure to the elements, including rain, snow, high wind, and sun exposure. All these factors can degrade the masonry of your chimney, eventually causing cracks and chips to form between the chimney’s bricks or stones.
Once small cracks form in the chimney’s structure, water can easily seep into these spots. During cooler weather. This means the water could freeze, thaw, and then refreeze, expanding the crack each time and eventually making the crack worse.
Chimney crown damage
The next possible source of rain entering your chimney is any damage to the chimney crown. This structure sits atop the chimney and typically features a sloped surface designed to allow rain to run off it and prevent it from entering the flue. If your chimney crown becomes cracked, chipped, corroded, or bent due to physical damage, these issues can easily interfere with proper water flow and allow rain to enter the flue. If there’s any problem with your chimney crown, it will be most noticeable during heavy rainfall.