Understanding Wind Uplift Ratings for Roofing

Understanding Wind Uplift Ratings for Roofing

2021 marks the seventh year in a row in which at least one named storm has developed ahead of the June 1 start date of the Atlantic hurricane season.

With this season off to a fast start, now is the perfect time to get your home prepared for the dangers that hurricanes can bring– especially since forecasters are predicting above-average activity this year. One of the most important attributes of your home’s roofing system is wind resistance, or the ability to withstand wind uplift. 

Although none of the systems devised are fool-proof, they can help you compare roofing construction and the probability of failure for each system you consider. 

Below, we review how wind uplift from severe weather affects roofing and examine the engineering behind a DECRA Metal Roof.

What is 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 results in a “push-pull” force working together to separate the roofing materials from the roof deck. Roof perimeter overhangs and windward corners, eaves, rakes and ridges are the most vulnerable roof areas to the damaging effects of wind uplift.

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.

What are Wind Uplift Lab Tests?

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 provides a rating, which reflects the last wind speed the roof is able to withstand before failing. A point of system failure occurs when the fasteners pull loose from its attachment to the underlying roof sheathing.

This is common in asphalt shingles that are not well bonded since the wind stagnates at the base, while aerodynamic wind uplift occurs at the top. The resulting lift can deform the shingle, exposing the underlying roof deck to more damage.

DECRA Metal Roofing fasteners, on the other hand, are specifically tested to provide the high-performance required to endure the rigors of wind resistance lab tests. 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 a different fastener can compromise the entire roofing system, especially in high-wind and corrosive salt-air environments.

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Tough TAS 125 Testing for High-Velocity Hurricane Zones

While many roofing manufacturers are satisfied with the performance requirements of UL 1897, DECRA takes its testing a step further. We submit our products to TAS 125 testing to ensure they comply with high-velocity hurricane zone requirements, including Miami-Dade, Florida, which is known as the region with the most severe wind market.

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.

While DECRA panels are backed by a warranty for winds up to 120 mph, they’re lab tested at twice that velocity. Additionally, DECRA roofs use a unique interlocking system that helps the profiles remain firmly in place when severe winds blow through.

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 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 for review and approval. These safety authorities divide the actual tested uplift point-of-failure value by a safety factor of two. That means the final rating is just half of the wind pressure endured to the point of failure in the lab.

This makes DECRA a top choice for homeowners who don’t want to deal with the damaging effects of storms year-after-year.

Get the Added Protection of a DECRA Metal Roof for Hurricane Season

DECRA roofs have stood up against wind uplift–among other elements–in hurricane-prone areas for more than 60 years. When you’re ready to upgrade to a one-and-done roofing solution that bridges the gap between industrial durability and architectural beauty, contact a DECRA roofing advisor.

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