Vented-Roof Design Eliminates Wind Damage

March 28, 2019 - by commarchtest

Brian Brookheart
Founding Member

In commercial roofing, wind-uplift calculations are performed on every building to determine the wind-uplift pressures that will be exerted on the building during its service life. Designers need to determine the uplift of the corners, perimeter, and field to properly design a roofing system.

UL1897 and FM4474 uplift tests measure a roofing system's ability to withstand pressure differentials. When a roof vent is installed in a test panel, the test results are negated. Roof vents equalize pressure differentials. Uplift pressures are not exerted upon the roof panel being tested and are transferred to the roof assembly or deck assembly beneath the vented roof membrane.

UL1897 and FM4474 uplift tests measure a roofing system's ability to withstand pressure differentials. When a roof vent is installed in a test panel, the test results are negated.

For example, if a roofing manufacturer constructs a 12 x 24-ft. roof panel and installs a vent in the middle of that panel, the results of the test say little about the roof assembly and instead are actually testing the roof deck. The vent will equalize pressure until the deck breaks. The numerical values obtained in the test are actually useless. They say nothing about the vent, the membrane or the vented roof’s ability to withstand wind. They speak volumes about the roof deck or “existing roof” assembly under the vented-roof membrane. It's for this reason that the third-party engineering lab that VADA and many other manufacturers use to test wind uplift will not test a panel with a vent in the assembly. The “uplift test” always fails when the roof deck breaks.

The system manufactured by Vada LLC, Olney, IL, is an over-engineered perimeter design that functions across the entire ASCE7 wind-uplift area. Perimeters are tested without a vent in the test assembly. Therefore, the numerical result of the wind-uplift resistance of a system's perimeter is an actual measurement of the system's ability to withstand pressure differentials. That fact is vital in actually designing a roof system.

Properly designed vented-roof systems will withstand the strongest of wind events.

With the approach we use, the ASCE7 requirements are calculated. Then, a VADA system that has been tested without a vent in the assembly is specified. For the roof shown in the accompanying photos, a 74-psf corner, 56-psf perimeter, and 38-lb. field were required. The specified perimeter design tested to 180 psf, without a vent. This tested design was installed throughout the ASCE7 uplift vortex area. In the roof field, where uplift is diminished, VADA vents were installed to create vacuum and equalize pressure.

With this design and approach (which carries three U.S. patents), we have not experienced any wind roof damage--from storms that have included hurricanes and EF3 and EF4 tornadoes--in more than 32 years of real-world applications. VADA provides a unique combination of ASCE7 vortex protection and project savings by eliminating materials and labor from the roof field of the roof.

For more information, contact Brian Brookheart at Brian@VADAVent.com.

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