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Roof Pressure Zones
1 2 3

Roof corners can see triple the suction pressure of the center! Click zones to explore why Miami-Dade roofing needs zone-specific design.

Roof Plan View - Click Zones
Wind
3
2
3
2
1
2
3
2
3
GCp (10 sq ft)
Zone 1 (Field)
-1.0
Zone 2 (Edge)
-1.8
Zone 3 (Corner)
-2.8
Low
Zone 1 Zone 2 Zone 3
High

Conical Vortices: The Corner Killers

When wind flows over a flat roof, something strange happens at the corners. The wind separates and spins into cone-shaped vortices that touch down right at the corner.

These conical vortices create intense suction - like a tiny tornado on each corner of your roof. That's why Zone 3 experiences pressures 2-3 times higher than the middle of the roof.

In Miami-Dade with 180+ mph winds, Zone 3 corner pressures can exceed 100 psf suction! That's enough to rip off roof membranes, tear out mechanical equipment, and lift pavers right off the roof.

Suction intensity varies by zone

Zone 1
-1.0
Zone 2
-1.8
Zone 3
-2.8

GCp values for 10 sq ft effective area

Nearly 3x the Pressure!

Look at those numbers: Zone 3 has a GCp of -2.8 compared to Zone 1's -1.0. That means corner pressures are nearly three times higher than the roof field.

This is why roofing specifications in Miami-Dade often call for enhanced attachment at perimeters and corners - more fasteners, closer spacing, thicker adhesive, or mechanical anchors.

Smart engineers and contractors use "enhanced perimeter and corner zones" with specific attachment patterns that recognize these pressure differences.

Zone Boundaries

Just like wall zones, roof zone boundaries are based on dimension "a" - the smaller of 10% of roof width or 40% of roof height, with minimums.

Zone 3 occupies the corner squares (a x a). Zone 2 extends "a" distance from all edges, except where Zone 3 takes over at corners. Zone 1 fills the remaining interior.

For a 100 ft x 60 ft building that's 30 ft tall, "a" would be about 6 feet. So Zone 3 covers 6 ft x 6 ft at each corner, Zone 2 extends 6 ft from edges, and Zone 1 covers the center field.

a = min(0.1L, 0.4h)
Zone 3
a x a corners
Zone 2
a from edge
Zone 1
Interior field (remainder)

Frequently Asked Questions

What are the roof pressure zones in wind load calculations? +
ASCE 7 defines three roof zones for low-slope roofs: Zone 1 (field/interior), Zone 2 (perimeter/edge), and Zone 3 (corner). Each zone has different GCp coefficients reflecting how wind pressures vary - highest at corners, intermediate at edges, lowest in the field.
Why do roof corners have the highest wind loads? +
Wind flowing over roof corners creates intense vortices called conical vortices. These spinning wind patterns generate extreme suction pressures that can be 2-3 times higher than the center of the roof, which is why Zone 3 has the highest GCp values.
What are typical Zone 3 GCp values for flat roofs? +
For flat roofs with small effective areas (10 sq ft), Zone 3 GCp can reach -2.8 to -3.0 for negative pressure (suction). This is significantly higher than Zone 1's typical -1.0 to -1.4 range, requiring much stronger attachments at corners.
How are roof zone boundaries calculated? +
Zone boundaries use dimension "a" which equals 10% of least horizontal dimension or 40% of roof height, whichever is smaller, but not less than 4% of least dimension or 3 feet. Zone 2 extends "a" from edges, Zone 3 covers the corner squares of dimension "a x a".

Get Zone-Specific Roof Pressures

Our calculator automatically computes Zone 1, 2, and 3 pressures for all roof surfaces. Essential for Miami-Dade roofing specifications and product approval.

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