Flashing around a metal chimney is an important component that helps prevent water infiltration and damage. The flashing creates a waterproof seal between the chimney and the roof surface. There are a few common reasons why you may see flashing reflecting light or ‘flashing’ around a metal chimney:
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Reflective Metal Flashing
Metal flashing, often made of aluminum or galvanized steel, is installed around chimneys during construction. This metal is highly reflective and when hit by sunlight can appear to be flickering or flashing. This is normal and not necessarily indicative of any issues.
Loose or Damaged Flashing
Over time, flashing can come loose or become damaged due to weathering. Gaps in the flashing or loose edges that move in the wind may cause intermittent flashes of light reflection. Damaged flashing should be repaired to prevent potential water damage behind the chimney.
Thermal Expansion and Contraction
The metal used for flashing expands when heated by the sun and contracts as it cools. This inevitable expansion and contraction can cause the flashing to warp or move slightly. Sunlight catching these subtle motions can make it appear as if the flashing is flickering. As long as the flashing remains sealed, this thermal movement is not a problem.
Accumulated Moisture
Standing water or accumulated moisture behind loose flashing can also cause flashing. When the sun hits the water, it acts like a mirror and causes brightness or flashing reflections. Identifying and repairing areas where moisture accumulates is key to stopping this issue.
Corroded or Rusted Flashing
Over many years, metal flashing can start to corrode or rust. As the surface degrades, it becomes more reflective and prone to glinting in the sunlight. Corroded flashing should be replaced to prevent further deterioration.
Replacing Flashing
If flashing is excessively damaged or deteriorated, replacement may be necessary. This involves carefully removing the old flashing and installing new flashing around the chimney. Proper installation is crucial to creating a watertight seal. In some cases, full chimney repairs or rebuild may be needed if structural issues are identified.
When to Be Concerned
Occasional flashing is normal for metal chimney flashing. However, consistent flashing, flickering, or glinting may indicate a bigger issue. Signs of potential water damage like interior leaks, mold growth, or roof rot should also prompt chimney flashing inspection. It is recommended to have a professional roofer or chimney specialist evaluate any ongoing flashing concerns.
Conclusion
In summary, metal chimney flashing may appear to flash or flicker due to normal sunlight reflection. However, damaged, loose, or corroded flashing can also cause this effect and should be addressed to prevent water infiltration. Thermal expansion of metal and moisture accumulation can contribute as well. While occasional flashing is not a worry, consistent reflective light should prompt inspection and any needed repairs to preserve chimney and roof integrity.