Wind Effect on Commercial Roofs

Wind Effect on Commercial Roofs

During periods of sustained, powerful winds, it is important for building managers and owners to recognize that their roofing systems may go through significant stress. The strong winds typically associated with transitional weather events and winter storms have the potential to cause severe damage to flat roofs. Wind creates negative pressure that exerts an upward force on flat roofs, causing structural stress.

To assess the extent of wind damage to flat roof structures, it is essential to consider six key factors and four primary wind threats, along with the likely damage they can inflict on susceptible areas of commercial roofing.

6 Key Factors

1. Wind Speed: The intensity and velocity of the wind gusts impacting your roof can influence the extent of the damage. Increased wind speed is directly related to the potential for greater damage. Nevertheless, you would be mistaken to assume that only extremely high wind speeds hurt the condition of your roofing system. Wind speeds as low as 40 to 50 mph can generate sufficient force to dislodge or damage edge flashing or fascia. “Wind has a variety of considerations to take into account. It can knock a person over, blow supplies around, and cause a job-site to be highly dangerous. Flying projectiles can do some damage to workers and structures in the area. Debris can impact vulnerable systems by damaging wires, railings, anchor points, and more.” (Simplified Safety).
2. Wind Duration: The possibility of roof damage is not solely determined by the wind speed but also by its duration. Sustained low wind speeds have the potential to cause significant damage to a roofing system over an extended period.
3. Wind Direction: The severity of damage to your roofing system is also influenced by the direction of the wind. When the wind is blowing in the opposite direction of a roofing material, there is a high chance that, over time, the wind will successfully lift the material.
4. Roof Condition: When a roof is in a state of disrepair, even a moderate amount of wind can generate damage. A roof that is inadequately maintained is significantly less likely to withstand extreme weather conditions compared to one that is regularly and properly maintained.
5. Material Quality: Durable roofing materials are more likely to withstand strong winds compared to less expensive materials.
6. Expert Installation: It is crucial to engage the services of skilled professionals when undertaking a roof replacement or new roof installation project. The workmanship level directly influences the roof’s performance in withstanding environmental elements, particularly wind.

4 Primary Wind Threats

Various classifications of strong winds can cause damage to your flat roofing system. Although hurricanes and tornadoes account for a considerable portion of the damage, more than half of the severe wind-related damage is attributed to the powerful winds generated during intense thunderstorms.

1. Hurricane Winds: Hurricane winds are winds exceeding 74 mph. Elevated wind speeds at lower levels frequently result in widespread destruction, leading to the airborne dispersal of various objects such as tree branches, paper, and packaging. The maximum wind speed of the most powerful hurricanes generally reaches approximately 200 mph. As a result of the extended duration of these storms, they can continuously impact commercial buildings and facilities.
2. Tornado Winds: Tornado winds are highly destructive natural forces. A tornado is a swiftly moving and intense storm that can span several hundred miles. It has the potential to generate powerful winds, reaching speeds of up to 300 mph in the most severe storms. Although prolonged high hurricane winds can result in extensive damage, tornadoes can destroy sturdy structures within a matter of seconds.
3. Straight-Line Winds: Straight-line winds emanate from thunderstorms and encompass wind gusts of 100 mph or greater. These winds have the potential to cause significant damage to roof systems and building structures.
4. Derecho: A derecho is a prolonged and extensive straight-line windstorm that lingers over vast regions. This phenomenon is frequently linked to rapidly moving thunderstorms. A derecho is characterized by wind-related damage that spans over 240 miles and involves wind gusts of at least 58 mph.

Vulnerable Roof Areas

With a flat roofing system, the corners and edges of the roof are the most susceptible areas to wind damage such as perimeter flashing. “Roof flashing refers to the strips of metal or other material installed around the roof edge where the roof cover meets the wall. When the flashing is compromised, it leaves important building systems including the roof cover vulnerable to the elements (such as wind-driven rain) which can cause significant damage.” (Disaster Safety).

The vulnerability of these areas becomes apparent when damage to the perimeter of the roof causes it to peel back and lift. In extreme circumstances, the wind pressure has the potential to infiltrate beneath the roof and effectively dislodge it from the structure.

Wind Uplift

One significant issue that impacts flat roofs is wind uplift. This phenomenon occurs when strong air gets beneath the roofing material and lifts it. This prevalent issue can cause the formation of wrinkles or bubbles on the roof’s surface, caused by the inadequately firm and secure attachment of the membrane or material.

It is important to consider that when a loose or detached roof membrane lifts from the surface, rain or moisture may seep into the system, leading to the deterioration of the underlying materials and rendering the entire roof ineffective. To prevent wind uplift, roof flashing must be properly installed and in functional condition. In the event of loose fascia boards or their dislodgement by strong winds, there is a risk of the metal flashing also being torn off.

Wind Scouring

Besides wind uplift, flat roofs frequently encounter another wind-related issue known as scouring, which refers to the phenomenon in which strong winds remove snow from windward slopes. This phenomenon occurs when the force of the wind is sufficiently strong to dislodge the protective granules from the roofing membrane or to displace the gravel that has been applied as a surface coating on Built-Up Roofs (BURs).

Although there may not be an immediate or clear sign of damage caused by wind, wind scouring can have a hazardous impact on the longevity of commercial flat roofs. The roofing system may exhibit signs of wear and deteriorate more rapidly than expected. The occurrence of partial or complete roof failure may cause the immediate installation of a new roof.

PB Roofing’s THREATCheck

THREATCheck: one enhanced visual inspection to identify deficiencies and provide recommendations for repairs or replacement. Our Plus Package shares the same features but with an added bi-annual inspection plan. Photo report included.

Any existing issues with your flat roof will be identified and effectively repaired. Even minor concerns have the potential to escalate into significant challenges when subjected to strong winds. Prioritizing the maintenance of your flat roof before the onset of winter can reduce the likelihood of significant damage caused by strong winds.

Resources

Disaster Safety: Business Protection Guidance to Reduce Hurricane Risks

Nationwide Insurance: Protecting Roof-Mounted HVAC Units from Severe Weather

National Weather Service: High Wind Safety Rules

PB Roofing Blog Back Issue (September 2023) “Connecting the Top 4 Ways to Understand, Identify, Prevent and Fix Freeze-Thaw Damage”