Understanding Wind Uplift Ratings for Roofing
The 2020 Atlantic hurricane season is off to the fastest start in recorded history and warmer ocean temperatures are expected to generate hurricanes and tropical storms with much more frequency and intensity. With extreme wind events on the rise, now is the time to protect your home or building with a wind-resistant roofing system.
Let’s take a look at how wind uplift from extreme weather affects roofing and examine the engineering behind the superior wind protection of DECRA Metal Roofing.
Defining Wind Uplift
Wind uplift is created when the air pressure below the roofing system is higher than the air pressure above the roof. Keep in mind that the roofing system includes the surface materials and the fasteners used to attach them to the roof deck.
Whenever the wind blows over a roof’s surface, the air pressure directly above the roof decreases. This is called “negative” pressure. At the same time, the wind causes air infiltration below the roof materials through openings and cracks that create a “positive” pressure. The combination of negative pressure above and positive pressure below the roofing surface materials results in a “push-pull” force working together to separate the roofing materials from the roof deck. Further, roof perimeter overhangs and corners are also the most vulnerable roof areas for damaging wind uplift forces to occur.
Wind uplift is affected by:
Building height: Higher roofs experience stronger wind velocities.
Geographical location: Wind maps for any region can identify the local basic wind speed gust exposures to determine typical wind conditions for your home.
Surrounding terrain: Neighboring buildings and other obstructions can break wind flow and reduce the wind effect in suburban and urban locations. Stronger wind resistance is required for roofs near large bodies of water or open terrain.
Building openings: Openings in the building design can create higher internal pressures in a wind event.
Steep-sloped roofs are extremely prone to higher wind uplift pressures. You can get a sense of this by imagining the immense increase in wind uplift pressure experienced when you angle your hand more steeply out of a moving car window.
Wind Uplift Lab Testing and Industry Standards
UL 1897 Testing is the roofing wind resistance standard that ensures compliance with the International Residential Code (IRC) or the International Building Code (IBC) on which most U.S. building codes are modeled. The test increases PSF in increments and records pressure at the moment the roof system experiences wind uplift failure.
In laboratory testing, wind uplift forces are applied and carefully measured in Pounds per Square Foot (PSF), gradually increasing the PSF force until roof system failure occurs.
A common point of system failure occurs when fasteners shear or pull loose from the underlying roof sheathing.
DECRA fasteners are specifically tested to provide the high-performance required to endure the rigors of wind resistance lab tests and meet actual roof system installation requirements in the field. The DECRA #10 x 1.5” corrosion-resistant fastener with a ¼” drive hex bolt head with integral steel washer is approved for use in High-Velocity Hurricane Zones by Florida’s Miami-Dade building code which is the strictest code in the U.S. Important fastener attributes include superior withdrawal force and lateral shear force tolerances, and high corrosion resistance.
For this reason, it’s very important to use only DECRA fasteners to avoid compromising wind performance in DECRA roofing systems. Substituting with an inferior fastener can compromise the entire roofing system especially in high-wind and corrosive salt-air environments.
Tough TAS 125 Testing for High-Velocity Hurricane Zones
While many roofing manufacturers are satisfied with the performance requirements of UL 1897, DECRA sets the bar much higher by submitting all of our products to TAS 125 testing to ensure they meet the highest wind resistance standards set by the State of Florida and Miami-Dade County for roofs in High-Velocity Hurricane Zones. Coastal Texas gulf regions recognize DECRA wind uplift resistance performance per the Texas Department of Insurance directory listings.
With TAS 125, positive and negative wind pressures are applied in cycles in a sealed test chamber. These challenging cycles subject the roofing system to pressures prescribed in the highest UL 580 Class 90 standard. The PSF applied pressure approximates indicated wind velocities for the highest Class 90 wind resistance encountered in hurricane conditions.
The DECRA Wind Warranty Safety Factor
With TAS 125 testing completed at pressures equivalent to the strongest hurricane winds, how does DECRA determine the wind warranty speed at 120 mph? Shouldn’t it be higher when the tested point of failure PSF equivalent is close to 240 mph? That’s because there is a 100% safety factor due to our nation’s demanding building code wind uplift requirements. For the hurricane-prone state of Florida and Atlantic coastal regions extending northward, even higher wind uplift resistance is called out by code that is accomplished by required high wind installation methods.
DECRA submits our independent laboratory wind uplift test results to various building code compliance agencies and code jurisdictions including the ICC Evaluation Service (ICC-ES) for International Residential Code (IRC) and International Building Code (IBC) requirements, the Miami-Dade Building Code Compliance Office’s Product Control Division, and the State of Florida Building Code offices for review and approval.
These safety authorities divide the actual tested uplift point-of-failure value by a safety factor of 2. That means the final reported DECRA PSF rating is actually just ½ of the wind pressure endured to the point of failure in the lab. DECRA roofing systems endured twice the reported lab-simulated wind velocity.
DECRA Metal Roofing for Lifetime Durability
DECRA Metal Roofing products are unmatched for superior wind and weather resistance in all regions and all seasons. Combined with DECRA fasteners and lab-tested installation techniques, DECRA is the walkaway winner in every roofing performance category for lifetime durability
Contact an expert DECRA advisor today to join more than 1 million homeowners and building owners who have chosen DECRA to protect their properties from extreme weather events.