Hurricane Roof Damage

Tropical cyclones are called hurricanes in the Atlantic and northeastern Pacific, typhoons in the northwestern Pacific, and cyclones or severe cyclonic storms in the Indian Ocean and South Pacific. Whatever the local name, the roof is usually the first part of a building to fail, and roof damage is a leading cause of the water damage that follows a storm.

Post-storm investigations by the US Federal Emergency Management Agency (FEMA) and others, from Hurricane Andrew (1992) to Hurricane Michael (2018), show the same chain of failures repeating: the roof covering is lost first, water then enters through the exposed deck, and in stronger winds the deck and framing can be lifted away.

How wind attacks a roof

Wind flowing over a building creates suction (negative pressure) on the roof surface. Suction is strongest at corners, eaves, rakes, hips and ridges, which is why damage tends to start at these locations. If a window, door or garage door is broken, wind entering the building adds internal pressure that pushes the roof upward from below, greatly increasing the load on the roof deck and its connections.

Common failure modes

• Roof covering loss. Shingles, tiles and panels are torn off when fasteners are too few, misplaced or poorly driven, or when sealant strips do not bond. Investigators after the 2004 Florida storms and after Michael repeatedly found shingle nails placed too high on the shingle.
• Edge and ridge failures. Drip edge, fascia, gutters, ridge caps and ridge vents fail early because pressures there are highest. Lost ridge vents leave an open slot in the deck.
• Soffit failure. Soffit panels that blow out let wind-driven rain into attics, even on roofs that otherwise survive.
• Deck (sheathing) loss. Panels pull off rafters or trusses when nailing is inadequate, often after the building envelope is breached.
• Structural loss. In the most severe winds, weak roof-to-wall connections allow the entire roof structure to lift off.

Water intrusion

Even moderate damage can lead to large losses. Wind-driven rain entering through missing coverings, open deck joints, vents and soffits soaks insulation and ceilings and promotes mold. After Michael, FEMA noted buildings that were unusable for extended periods because of this water damage rather than structural failure.

Codes and mitigation

Florida strengthened its code after Andrew, and later reviews found that homes built under newer rules in Charlotte County needed fewer roof covering replacements than older homes after the 2004 storms. Current mitigation focuses on a continuous load path (deck nailing and roof-to-wall connectors), stronger edge details, wind-rated coverings, and a secondary water barrier or sealed roof deck. Programs such as FORTIFIED in the United States package these measures into a designation.

Saffir-Simpson scale and roofs

The US National Hurricane Center's Saffir-Simpson Hurricane Wind Scale describes expected damage to well-built homes by category: Category 1 (119-153 km/h, 74-95 mph) damages roof coverings and gutters; Category 3 (178-208 km/h, 111-129 mph) can remove roof decking and gable ends; Category 5 (252 km/h, 157 mph or higher) can cause total roof failure. The scale rates wind only, not storm surge or rainfall.