Roof flashing leaks: why flashing fails around chimneys, walls and valleys, the warning signs and how repairs work. Learn what to check and when to call.
Roof flashing is the thin, waterproof material fitted where the roof meets something else — a chimney, a vent pipe, a skylight, a wall, or another roof slope. It is usually made from metal, such as aluminium, copper, or galvanised steel, though other materials are also used. Its job is to seal the joints where water is most likely to get in. Shingles overlap to shed water, but at a joint — where the roof meets a vertical surface, or where two slopes meet in a valley — overlapping shingles alone are not enough. Flashing bridges that joint and directs water away from it.
Flashing is one of the most important parts of a roof, and one of the most common sources of leaks. A roof can have sound shingles and still leak, if the flashing has failed. This guide explains why flashing leaks, where it happens, and how it is fixed.
Flashing is fitted in several places on a typical roof, and each one is a potential leak point:
Flashing does not last forever. Metal flashing can corrode or rust over time, especially if it is not the right metal for the conditions, or if it is in contact with a different metal that causes corrosion. Rubber collars on vent pipe boots can crack and shrink with age and sun exposure. Sealant used around flashing can dry out, crack, and shrink. As flashing ages, it becomes less able to seal the joint, and water can find its way through.
Flashing needs to be fitted correctly to work. If step flashing is not overlapped properly, if counter-flashing is not fitted into the chimney, if a vent boot is the wrong size for the pipe, or if valley flashing is not wide enough, water can get in from the start. Poor installation is a common cause of flashing leaks on newer roofs, and it is one reason why the quality of the installation matters as much as the material. If a roof leaks around a chimney or vent and the roof is relatively new, poor flashing installation is a likely cause.
Roofs expand and contract with temperature changes, and different materials expand at different rates. A chimney, for example, does not move in the same way as the roof around it. Over time, that movement can loosen flashing, open up gaps, or crack sealant. In Phenix City's climate, with hot summers and cooler winters, that cycle of expansion and contraction happens year after year. Flashing that was fitted tightly when new can work loose over time.
Strong wind can lift or bend flashing, or pull it away from the surface it seals. Hail can dent flashing. Fallen branches can damage flashing around a chimney or vent. After a storm, flashing is one of the things to check — see our storm damage roof checklist and our guide to the signs of wind damage.
Sealant (caulk) is useful for sealing small gaps, but it is not a substitute for properly fitted flashing. If flashing is missing, badly fitted, or damaged, and sealant is applied over the top, it may stop the leak for a while, but it will not last. Sealant dries out and cracks, and the leak returns. A lasting fix usually involves removing the old flashing and fitting new flashing correctly, not just adding more sealant.
Valleys and gutters that are blocked with leaves and debris can cause water to back up and sit against flashing, rather than draining away. Standing water is more likely to find its way through a small gap in flashing than water that is flowing freely. Keeping valleys and gutters clear is a simple way to reduce the strain on flashing — see our roof maintenance checklist.
A proper flashing repair usually involves more than sealant. The general approach is:
The cost of a flashing repair depends on where the flashing is, how much needs to be replaced, and whether the deck or underlayment is also damaged. See our guide to roof repair cost factors.
You can check flashing from the ground with binoculars, and from inside the attic. Look for:
Do not climb onto the roof to check flashing, and do not try to refit flashing yourself. Flashing work needs to be done correctly to last, and it involves working on the roof. Note what you found, take photos from the ground, and arrange a professional inspection if anything looks wrong.
Sealant can be a temporary measure for a small gap, but it is not a lasting fix for damaged or poorly fitted flashing. Sealant dries out and cracks over time, and the leak is likely to return.
It depends on the material, the installation, and the conditions. Metal flashing can last many years, but it can corrode or work loose over time.
Often, but not always. A leak around a chimney is commonly a flashing problem, but it can also be caused by a damaged chimney cap, cracked mortar, or a problem with the roofing material near the chimney.
It depends on where the flashing is, how much needs to be replaced, and whether the underlayment or deck is also damaged. A small vent boot replacement is generally simpler than refitting chimney flashing.
Generally, yes. When a roof is replaced, the old flashing is usually removed and new flashing is fitted as part of the job.
Step flashing is a series of small, overlapping pieces of flashing fitted where a roof meets a vertical surface, such as a chimney or a wall. Each piece overlaps the one below it, like steps, so water runs down over the flashing and off the roof. It is a common and effective way to seal that joint, when fitted correctly.
Call (334) 772-1151 to discuss your roofing needs or check service availability in Phenix City and nearby Alabama communities.
We provide local roofing information and may connect homeowners with independent roofing service providers. Service availability depends on the provider and location.
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We provide local roofing information and may connect homeowners with independent roofing service providers. Service availability depends on the provider and location.