Atlanta averages roughly 50 inches of rain a year, and its summers bring long stretches of strong sun and heat. Both are hard on the asphalt-based sealants around every plumbing pipe, HVAC exhaust, and vent on a roof. Asphalt holds up in direct sunlight for years, but it doesn't last forever. Once the sealant cracks, rainwater has an easy path around the penetration and into the attic.

Nails are the other weak point. Most of them stay put through years of hot and cold weather, but a few lose their grip and back out. A popped nail can lift the shingle above it enough for wind-driven rain to get underneath, or it can push through the shingle and leave an open hole.

The city's heavy tree canopy also plays a part, since leaves and pine needles collect in gutters and roof valleys and hold moisture along the roof edge. We recommend roof maintenance every 8 to 10 years to deal with all of this while it's still minor.