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Calculate Overhang Loads
The Roof Edge Weak Point
Your roof overhang sticks out like a shelf in a windstorm. Wind rushes under it and tries to rip it off - that is why soffits fail first. Let's show you exactly what happens.
Wind Flow Around Roof Overhang
The Shelf in a Windstorm
Picture your roof overhang like a shelf sticking out from a wall. Now imagine a powerful fan blowing from the side. The air rushes under the shelf and pushes up - hard. At the same time, air flowing over the top creates suction that also pulls upward.
Your overhang gets attacked from both directions at once. That is why it sees loads 2-3 times higher than the middle of your roof.
Why Soffits Blow Off First
Those soffit panels under your overhang are held up by small nails or staples. During a hurricane, the wind pressure underneath can reach 95 pounds per square foot or more. That is like someone pushing up on every square foot with almost 100 pounds of force!
When those fasteners let go, the soffit panels fly away. Now wind and rain pour into your attic. This is how many roofs start to fail.
Example: 35 psf x (-2.8) x 1.0 = -98 PSF uplift
The Miami-Dade Solution
In the High Velocity Hurricane Zone, we design overhangs with respect for wind. Smart builders keep overhangs to 12-18 inches and use hurricane-rated fasteners. The soffit panels get screws every 6-8 inches instead of staples every 12 inches.
Wider overhangs need metal straps connecting the rafter tails directly to the wall studs below. No more relying on just nails to hold everything together!
Roof Overhang Questions
Why do roof overhangs experience higher wind loads than the main roof?
Roof overhangs experience higher wind loads because wind accelerates as it wraps around the roof edge, creating intense suction on both the top and bottom of the overhang. The soffit underneath gets pulled by negative pressure while the top surface also experiences uplift. This double-sided attack can create loads 2-3 times higher than the main roof field.
What is the typical wind load on a roof overhang in Miami-Dade HVHZ?
In Miami-Dade's High Velocity Hurricane Zone with 180+ mph design wind speeds, roof overhangs typically experience uplift pressures between -80 to -120 PSF. Corner overhangs can see even higher pressures exceeding -150 PSF. The exact value depends on overhang width, roof height, and exposure category.
How wide can a roof overhang be in Miami-Dade County?
While there is no strict maximum width, overhangs beyond 24 inches require increasingly robust connections. Most residential overhangs in HVHZ are kept to 12-18 inches to manage uplift forces. Wider overhangs need engineered connections with metal straps or hurricane clips rated for the calculated loads.
What causes soffit panels to blow off during hurricanes?
Soffit panels fail when uplift pressure underneath the overhang exceeds their attachment capacity. Wind pushes up on the soffit while simultaneously pulling the roof structure upward. If soffit fasteners are too weak or spaced too far apart, the panels pop off, allowing wind and rain into the attic and potentially leading to roof failure.
Calculate Your Overhang Wind Loads
Get exact uplift pressures for your specific overhang dimensions, roof height, and Miami-Dade location. PE-stamped calculations in 24 hours.
Calculate Overhang Wind Loads