Metal roofs are known for their long, leak-free lifespan, but they aren't completely immune to leaks. There are quite a few ways a leak can occur, but knowing what they are can help you avoid leak issues. 

1. Gasket Failure

The screw fasteners used to hold your metal roof panels in place are sealed with a gasket that sits between the roof and the screw head. Over time, these gaskets can deteriorate and a leak can occur at the screw site. Another issue is that screws can work loose over time, loosening the gasket, or driven in too deeply, which causes the gasket to lift around the edges. An annual inspection catches these issues so the gaskets can be replaced before leaks occur.

2. Corroded Fasteners

Another issue with the screws is that they often do not last as long as the roof itself. They can rust and corrode over time. They also tend to work their way out on occasion, usually due to temperature fluctuations. Replacing fasteners as soon as they show signs of damage prevents leaks. An annual inspection is also important so you can catch damaged or missing screws before extensive water damage becomes an issue.

3. Damaged Boots

Boots are the rubber seals that are placed around vent stacks and pipes that protrude from your metal roof. They act as a sturdy seal to keep moisture from leaking under the metal roof panel at the point of pipe penetration. Over time, the boots will begin to crack and leaks will develop. When this happens, the best solution is to have the boot replaced.

4. Weakening Sealants

Various sealants are used on a metal roof. The seams between panels are sealed, as are the seams under trim pieces or around the upslope edge of roof accessories like skylights. When the seal fails, water running down the roof can seep under a panel and cause a major leak. Sealants may need to be reapplied every decade or so, depending on the local weathering effects on the sealant.

5. Accessory Issues

A roof can have many accessories — solar panels, skylights, or chimneys for example. If these aren't installed or sealed properly, then leaks occur at the site of the accessory. Skylights, for example, may need a rain diverter placed above them on the roof so water doesn't collect along the top edge, and chimneys require proper step flashing. Accessory installers aren't always roofers, so they may not catch an issue. Have a roofer on hand to inspect the accessory installation so they can make sure it was done correctly. 

Contact a residential roofing contractor for more assistance if you suspect a leak on your metal roof.