Protect Your Roof From Storm Damage

Know what to do before, during, and after an extreme weather event


Remove ice from rooftops quickly to avoid disaster.

Snow and ice must be removed from rooftops in a timely manner. They can clog drains or melt and leak into the assembly. To avoid these failures and even worse disasters like caved in assemblies, have a removal plan that includes where the snow should be dumped. Also ensure that only trained roof technicians are performing snow removal, as they are trained in how not to damage the surface.

Respond to Avoid Disaster

What to Know about Wind

Although it's a common expression, roofs don't exactly "blow off." Familiarize yourself with other windstorm misconceptions and phenomena.

  • Factory Mutual (FM) Global, a testing laboratory that certifies materials, offers windstorm classification ratings such as I-60 and I-90. Many falsely believe the numbers refer to wind speed in miles per hour (mph). They actually apply to wind uplift pressures in pounds per square foot (psf).
  • Roof damage caused by wind occurs when air pressure below the roof assembly is greater than air pressure above the roof. As wind blows over the building, the pressure above the surface decreases, while simultaneously internal air pressure increases due to air infiltration. The result is a net upward force on the roofing system, referred to as wind uplift, bringing about the "blowing off" phenomenon.
  • A variety of factors affect how a building performs in high winds, including the building's overall height, the terrain surrounding the structure, and the type of roof deck used, among other criteria. FM Approvals account for all these considerations.

Information courtesy of FM GLOBAL

A windstorm can result in several kinds of damage. Protected membrane systems are vulnerable at the support board attachment to the structural deck, according to the RCI report Wind Uplift Resistance Evaluation of Commercial Roofs With and Without Add-ons.

In a lab setting with a pressure difference of 125 psf, metal plates and fasteners pulled through the support board, causing delamination of the membrane and air intrusion. PV modules and vegetated trays are also susceptible to damage and movement under these conditions, the report notes.

After a winter storm, snow must be removed in a timely manner to prevent it from clogging drains or melting and leaking into the assembly.

"One of our clients has a large canopy between the parking lot and facility. There was a major snowstorm, and everything became encapsulated in snow and ice. When it warmed up, the water had nowhere to go because the drain was encased," McBride explains. "Snow slid off the canopy onto the main ticket lobby roof and caved in part of the deck. It was a major event that impacted a lot of people."

Even extreme cold without precipitation poses threats. Another of PRC's clients didn't inspect the roof after a stretch of severe cold and didn't realize the roof had contracted to the point of cracking.

"When the cold weather went away, it started raining, and water just poured in," McBride explains. "The roof was split wide open like the Grand Canyon."

Reacting quickly becomes especially crucial if you can't personally make it to the site due to the nature of the storm.

"If your second in command points out that several ceiling panels have dropped out of the hung ceiling in the office, is he aware that it is probably due to the roof deck being deflected from ponded water? Does he know where the emergency roof gear is stashed?" Fricklas says. "Protective clothing and lighting should be available for the team to get up on the roof and open blocked drains before it collapses."

A computerized roof file will be handy when you need to know the location and warranty status of different roof systems. Make sure the system has a backup and that it can be accessed remotely.

"It's also wise to have maintenance contracts with local roofing contractors who offer 24/7 emergency roof service," Fricklas adds.

Assess and Repair Damage
After a storm, many facets of the roof system could be affected including its thermal performance, fire resistance, load and equipment carrying capacity, ability to drain and store water, and aesthetics.

But before calling in an expert, ask yourself if the damage observed is consistent with the intensity of the storm. Should the roof have performed better? It's likely that some damage is the result of an ongoing problem like poor drainage or inadequate ventilation. Answering these questions is helpful when dealing with warranties and insurance claims.

"The damage observed may often be present among several other construction, design, and maintenance issues," says David P. Amori, vice president of engineering at consulting firm EFI Global. "This convolution is the basis for discrepancies in the scope of repairs and cost."

An expert forensic evaluation determines if the roof is repairable or requires replacement, adds Amori. It begins with observing the interior upper floor for signs of water infiltration such as discoloration or delamination of finish materials. You may need to test the roof system or components to delineate whether the roof membrane, insulation, or any other parts of the assembly need to be removed.

In both PRC cases mentioned above, the remedies required replacement of only the impacted areas.

"We were able to get in touch with the manufacturer and explain that these defects should be covered by the warranty," McBride says. "We worked together. Manufacturers sometimes tell owners, 'Sorry, not included.' But that may not be acceptable. You have leverage."

Your roof can endure brutal impact from the elements. Don't relegate it out of sight and out of mind. "One of the most forgotten and neglected building systems also happens to be one of the most complicated," Amori says.

Avoiding costly remedies requires due diligence in preparation, response, and assessment. Perhaps most importantly, perform the majority of your due diligence during the calm before the storm.

"Be proactive with your roof and maintenance," McBride warns. "Whether you have been or not usually shows up after an extreme weather event."


Chris Curtland is assistant editor of BUILDINGS.


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