When to use: Estimate wind uplift pressure on roof components and cladding per ASCE 7-16 Chapter 30. Compute the velocity pressure qz, apply the roof-zone external pressure coefficient GCp combined with internal pressure GCpi, and size the net uplift and required fastener force. Corner (Zone 3) and edge (Zone 2) regions govern fastener attachment of decking, membrane, and panels.
Calculate wind uplift pressure on roof components and cladding per ASCE 7-16 Chapter 30. Compute velocity pressure qz, apply the roof-zone external pressure coefficient GCp and internal pressure coefficient GCpi to find net uplift pressure, then convert to fastener pull-out force for roof decking and membrane attachment design.
Velocity pressure: qz = 0.00256·Kz·Kzt·Kd·V² (psf), where Kz accounts for exposure category height effects, Kzt is the topographic factor (1.0 for flat terrain), and Kd is the wind directionality factor (0.85 for buildings). Net C&C uplift pressure: p = qh·(GCp − GCpi). The force per fastener or panel anchor F = |p|·A_trib.
Velocity pressure: qz = 0.00256·Kz·Kzt·Kd·V². Net pressure (uplift): p = qh·(GCp − GCpi) where GCp is negative (uplift) and GCpi is positive (outward internal). Roof zones: Zone 3 (corners) GCp ≈ −2.8; Zone 2 (edges) GCp ≈ −1.8; Zone 1 (field) GCp ≈ −1.0. Enclosed building internal pressure: GCpi = ±0.18.
Use when designing roof fastening patterns for metal decking, single-ply membrane roofing, photovoltaic panels, or roof cladding. Corner and edge zones require tighter fastener spacing than field zones due to higher GCp magnitudes. Tributary area per fastener determines the design pull-out force, which is compared to the fastener withdrawal capacity from the manufacturer or code tables.
ASCE 7 Chapter 30 divides roofs into three C&C zones: Zone 1 (interior field) with the lowest uplift, Zone 2 (edges within a distance of 10% of the least building dimension from the eave) with intermediate uplift, and Zone 3 (corners) with the highest uplift coefficients. Corners and edges must always be designed with the more severe GCp values.
Kz accounts for the variation of wind speed with height and terrain roughness. Exposure B (suburban) gives lower Kz (~0.70 at 30 ft) than Exposure C (open terrain, ~0.98 at 30 ft) or Exposure D (coastal, ~1.16 at 30 ft). Values are tabulated in ASCE 7 Table 26.10-1.
GCpi is the internal pressure coefficient. For an enclosed building, GCpi = ±0.18 (positive or negative). Worst-case uplift occurs when internal pressure is outward (GCpi = +0.18) combined with external suction (negative GCp). The net effect p = qh·(GCp − GCpi) amplifies uplift when both act together.
Multiply the net uplift pressure p (psf) by the tributary area per fastener A_trib (ft²): F = |p|·A_trib (lb). For example, 80 psf uplift on a 4 ft² fastener tributary area gives F = 320 lb. This is compared to the fastener pull-out or pull-through capacity from the roof system manufacturer's approved technical literature.