Wind Uplift

Wind uplift is the upward force that wind places on a roof. As air speeds over and around a building, it lowers the pressure on the roof surface, creating suction. If air also enters the building through an opening, the pressure inside rises and pushes up on the underside of the roof. The two effects add together.

Uplift acts on every layer: the covering (shingles, tiles, panels, membranes), the fasteners and adhesives, the deck, and the connections from framing to walls. Each must be strong enough, and the forces must travel through an unbroken load path to the foundation.

Factors that affect uplift

• Wind speed. Pressure rises with the square of wind speed, so a modest increase in speed produces a much larger load.
• Exposure and height. Open terrain, coastlines and taller buildings see higher pressures than sheltered sites.
• Roof shape and slope. Hip roofs generally see lower uplift than gable roofs. Low slopes and overhangs can concentrate suction.
• Location on the roof. Corners, edges, ridges and hips have far higher pressures than the middle (field) of the roof. Design standards divide roofs into pressure zones for this reason.
• Openings. A broken window or failed garage door can raise internal pressure and sharply increase net uplift.

How uplift is handled in design

National standards translate a design wind speed into pressures for each roof zone. Examples include ASCE 7 in the United States, Eurocode 1 (EN 1991) in Europe, and AS/NZS 1170.2 in Australia and New Zealand. Roofing products are then tested and rated for uplift resistance. Low-slope systems are often tested to FM Global or UL uplift methods; asphalt shingles are classified by ASTM D3161 (fan-induced) and ASTM D7158 (sealant bond uplift), with ASTM D7158 Classes D, G and H corresponding to about 145, 193 and 241 km/h (90, 120 and 150 mph).

Field practice

Correct fastener type, number and placement often matter more than the product itself. Post-storm investigations frequently find shingle nails placed above the nailing line, too few fasteners at edges, or deck nails that missed framing. Enhanced fastening at corners and perimeters, ring-shank nails for decks, and sealed edges are common upgrades in high-wind regions.