Few Roofing Products can compete with metal roofing in terms of longevity, strength, and performance. Having said that, metal roofs are not invincible and can leak. Here are five main reasons why even well-installed metal roofs might leak.
- roofing screws made of metal
The majority of leaks on metal roofs are caused by roofing screws. Metal roofing screws keep water out by squeezing a rubber washer at the screw head’s base. When the screw is inserted into the metal roofing panel, the rubber washer creates a “gasket” between the panel and the screw head. It appears easy enough, but various things may go wrong, such as under-driving screws, over-driving screws, driving screws at an angle that is not correct, and screws that miss the frame component.
Overdriven screws: Many roofing firms may overdrive the screw in order to achieve a tight seal between the metal roofing and the screw head. Unnecessary torque fractures the rubber washer and causes it to spin to the side.
Underdriven screws: occur when there is insufficient tension on the screw to effectively seat the rubber washer to the metal roofing panel. There is no compression of the rubber washer and no formation of a gasket.
Screws driven at an angle: These prevent the rubber washer from sitting flat on the metal roofing. A portion of the screw is sealed, but another portion is not.
Screws that have slipped through the metal strut or wood framing: These have nothing against which to seal. These can be difficult to locate since the screw is often present, but without touching it, you wouldn’t know that it didn’t strike anything and didn’t seal.
Even if the screws were placed correctly and with the proper amount of torque, the rubber washer is still not safe. Hot summers followed by harsh winters are harsh on rubber washers. They deteriorate and lose their seal, making it impossible to tell which screw is leaking and which is not.
- Flashings stacked
The region surrounding stack flashings is another high-risk location for leaks on a metal roof. Stack flashings are the “boots” or flashings that surround pipes that protrude from the metal roof. HVAC vents, air vents, and plumbing lines must all vent through the metal roof. The stack flashing protects the pipe from water. The majority of stack flashings are made of rubber or rubberized material that rests flat on the metal roof and provides a seal while also “squeezing” around the pipe to make another seal. The movement of the metal roofing due to expansion and contraction is constantly putting these seals to the test.
The sun also deteriorates the rubber flashings, which only last roughly half as long as the metal roof. The more caulking, sealer, or tar applied beneath and around the stack, the more they appear to pond water and leak; it’s a catch-22 situation.
To keep your building dry, plan on repairing old or rotted stack flashings.
- a lack of sealants
Metal roof sealants put in combination with a metal roof seldom survive as long as the metal roofing panels and must be updated as part of routine roof maintenance. Sealants beneath trims like metal ridge caps and Z flashings, around roof transitions, counter flashings, reglets, and pitch pans will all need to be “topped off” as they wear. Use a metal roof sealant designed exclusively for metal roofs. Other silicone caulkings could not stick to the paint on the roofing panels and trimmings. Metal roofing undergoes a daily expansion and contraction cycle, and any sealants that are to survive must be able to remain flexible and stretch with metal without breaking their seal.
- Flashings on the curb
HVAC units atop metal roofs are often installed on curbs. Installing metal roof panels is a pretty simple job, but it is the flashing that truly puts a metal roofer’s skills to the test. When it comes to HVAC, there is minimal room for mistake when it comes to manufacturing the flashing, and keeping a curb dry might be easier said than done. The uphill side of the curbs, as well as the two top corners of the curb flashing, are tough regions to work on, especially with larger HVAC units. Water frequently becomes trapped behind the unit and “stands” behind the flashing, eroding sealants and causing leaks. The more caulk, seal, or tar you apply to the uphill side, the more water it will hold. This Catch-22 is impossible to resolve without removing metal roofing panels and starting from scratch.
- Overlaps and seams
Seams where two sections of metal roofing overlap one other frequently leak due to a process known as capillary draw. When water can really move upward between two closely linked pieces of metal, this is known as capillary draw. Sealant or butyl tape between the two pieces of metal can interrupt the capillary pull, but if not applied appropriately, it can actually make leaks worse than if no sealant or butyl tape was used at all.
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