Wind blowing over a surface creates lift. Swiss physicist David Bernoulli published this fact in the year 1738. Wind blowing over the wing of this 747 creates enough lift to make the 900,000 pound plane fly, with the space shuttle riding piggyback. Wind blowing over an airplane’s wing is very beneficial to our lives.
That same force, wind blowing over the surface of a roof, also creates lift. In the photo (right), wind uplift has removed the roof, the insulation, and lightweight insulating concrete. The wind that caused the damage was a Category 3 hurricane with sustained winds of 135 mph. In this case, the effects of Bernoulli’s Principle caused damage and destruction.
Wind uplift occurs on every roof on every building, every time the wind blows. These forces must be counteracted or devastation occurs.
Historically, wind uplift was transferred to the building structure using adhesives. For centuries, hot asphalt was the “glue” that held commercial flat roofs together. Hot asphalt is still used today. However, many studies have documented the adverse health issues related to exposure to asphalt fumes.
When single ply roofing systems were introduced, hot asphalt was supplanted by solvent-based bonding adhesive. Adhesives were used to hold a roofing membrane in place. These adhesives contained numerous VOCs (volatile organic compounds). Chronic exposure to VOCs has been proven to produce numerous adverse health issues. On a 100,000 square foot roof, a VADA Vented Roof Assembly will prevent approximately 1,000 gallons of toluene, naphtha, acetone, xylene, ethylbenzene and other VOCs from entering the atmosphere. With VADA Vented Roof technology, a wind-resistant roof can be installed in a much greener and environmentally sound manner.
VADA Vented Roofs use vacuum-producing, air-moving ventilators to counter Bernoulli’s Principle. VADA’s ingenious design holds roofs on buildings. It is not only the use of VADA Vents that counters wind uplift; it is how and where we employ the vents.
Other vented roof companies require that roof vents be placed in the wind vortex at the perimeter of the building. For years, that was the prescribed method of venting a roof. After wind tunnel testing, we now know that the turbulent, rolling, violent air at the vortex is the worst possible scenario for vent efficiency. Roof vents need nice, calm, stable, straight, in-line air to perform at their best. Therefore, in spite of the “known” fact that vents are to be placed in the vortex, VADA Vents are NOT placed in the wind vortex. Our slogan is: “DON'T VENT THE VORTEX”. Those who do vent the vortex are diminishing the effectiveness of their vents.
VADA Vents are installed outside the known wind vortex of the roof. Therefore, our vents have perfect air in which to perform. And perform, they do.
In third-party, independent laboratory testing, VADA Vents were shown to produce 6 times more vacuum and move 23 times more air than competing roof vents. Rapid, accelerated movement of air is required to quickly evacuate air infiltration that occurs during wind gusts. Three-second gusts can devastate a roofing assembly if the air is not removed. These tests have been verified by Ph.D. engineers and aeronautical engineers. The science is indisputable.
VADA Vented Roofs employ a patent pending approach to countering the wind vortex area of the roof. This approach has been laboratory tested using tests such as the FM4474. These tests are performed by independent engineers.
Those who make and market vented roofs are under considerable pressure to prove that their vented roofs perform. In roofing, there are two widely known testing organizations, Underwriters Laboratory (UL 1897 test) and Factory Mutual (FM 4474 test). Since most accepted roofing systems are tested in this manner, vented roof manufacturers often feel obligated to run these tests.
UL 1897 Test: Definition: (From the UL)
1.1 The test method specified in this Standard is intended to provide uplift resistance data for the evaluation of the attachment of roof covering systems to roof decks by using differential air pressures. It is applicable to any type of roofing system which is adaptable to the test equipment.
When wind blows over the surface of a building, uplift is created. The UL 1897 test simulates uplift by applying vacuum to the top side of the test roof assembly. The test measures the roof’s ability to resist the known uplift force inside the chamber. Pressure is increased in 15 pound increments. The roof system must resist the pressure for 60 seconds, to pass the given pressure. As the test is conducted, an engineer calls out numbers every 60 seconds. “60, 75, 90, 105, 120,” until the roof assembly is broken by the pressure differential between the top and bottom of the roofing membrane.
The word differential is crucial in understanding the significance of this test. Negative vacuum pressure is applied. The test measures the roof’s ability to withstand the difference in pressures between the top side of the roof assembly and the bottom side of the assembly. Differential air pressures exist and are measured by the test. Without differential pressures, there is no test. The test is negated.
Vacuum Chamber is placed over the roof assembly. Vacuum is applied from the top until the roof assembly fails.
However, negating the test is exactly what some vented roof manufacturers do during their UL 1897 or FM 4474 tests. Vented roof companies cut the roof membrane and install a roof vent. If a hole has been cut in the roof, there will be no differential in air pressure between the top and bottom side of the membrane. The hole or vent allows the pressure to equalize. Thus no differential can be measured. Therefore, the test is void.
At this point in the test, a numerical value will be obtained. However, the numerical value is not measuring the vented roof, the vent, the vented roof system or assembly. The numerical value of the test without air pressure differential measures only one thing and that is the strength of the roof deck.
Everyone who has ever performed a UL 1897 or FM 4474 understands the information written above. However, some vented roof companies are quite fond of stating the numerical values for tests that have been negated or voided by manipulating the results, by cutting holes in the roofing system.
Some state that their vent surpassed a certain numerical value. In reality, a round hole in the membrane would accomplish the exact same result. Any roof vent, no vent, or a large tin can, would all read the exact same result. The point is not their vent, but the fact that the test has been voided by their non-scientific methodology. Yet, after the manipulated numerical values are obtained, they proudly state them as science and fact.
Even more interesting, think about how roof vents create vacuum. VADA Vents create vacuum by wind blowing over the vent and spinning fans. Most roof vents need wind to create vacuum. Yet, those with roof vents that require wind to create vacuum, claim that their roof vent created “X” pounds of vacuum, without wind, in a vacuum. The fact of the matter is, no wind, no vacuum. The chamber has vacuum. The chamber’s vacuum is created by a large external motor and is piped into the chamber with a six-inch hose. Thus, vent manufacturer’s vents create no vacuum. But, you’d never know that by reading their press.
Many colleges have a math class called “Lying with Statistics.” It is a study of how statistics are used to obscure the truth. VADA’s test results are fact. Some vent manufacturers may have taken the statistics class. As always, VADA’s approach is different. When VADA, LLC tested our vented roof system, we did so by the rules. No vents, no cuts, no holes were installed in our roof membrane. Our results were real. For example, VADA ran an FM 4474 test on perimeter attachment. The purpose was to ascertain the numerical value of a certain perimeter attachment design. Based upon the value of the test, the attachment specification could be increased or decreased to meet a specific need for a specific building. The tested assembly passed 120 pounds of pressure. The assembly failed at 34 seconds into the test at 135 pounds. (Remember, 15 pound increments.) In the real world, if wind uplift calculations tell us a building will have 55-pound pressure on the corners, we use our 120-pound specification to overcompensate. We assure that every corner and every perimeter has an augmented roof attachment. Then, inside the wind uplift vortex or perimeter, we install vents. Our vents move air and create vacuum. Our interior roof sheets that are loose laid often look fully adhered. In a high wind, there is no movement. No peel, no shear and no stress on the roof system. Our tests are real. Other vent manufacturers’ rhetoric is just full of holes.