Metal roofs last a long time but they don't last forever. Here are the top four reasons that even properly installed metal roofs in Indiana leak.
1. Metal roofing screws.
Roofing screws are responsible for the majority of leaks on metal roofs. Metal roofing screws seal water out by compressing a rubber washer at the base of the screw head. When the screw is driven into the metal roofing panel the rubber washer forms a "gasket" between the roofing panel and the screw head. It sounds simple enough but several things can go wrong like under driving screws, over driving screws, driving screws at the wrong angle and screws that missed the framing member.
Under driven screws: These result when not enough torque on the screw is used to properly seal the rubber washer to the metal roofing panel. The rubber washer is never compressed and no gasket is formed.
Screws that have missed the metal strut or wood framing below have nothing to seal against. These can be hard leaks to find as many times the screw is there but without touching it you wouldn't know that it didn't hit anything and didn't seal.
Even if the screws were installed correctly with the right amount of torque it doesn't mean that the rubber washer is safe. Hot Indiana summers followed by hard cold winters are unkind to the rubber washers. They degrade and loose their seal and it can be very difficult to distinguish which screw is leaking and which is not.
2. Stack flashings.
3. Missing sealants.
Metal roof sealants that are installed in conjunction with a metal roof rarely last as long as the metal roofing panels do and need to be replaced with regular roof maintenance. Sealants under trims such as metal ridge caps and Z flahsings, around roof transitions, counter flashings, reglets and pitch pans will all need to be "topped off" from time to time as they wear. Use a metal roof sealant specifically made for metal roofing. Other types of silicone caulkings may not adhere to the paint on the roofing panel and trims.
4. Holes.