Roofing Resilience

One of the most vulnerable parts of a building during a storm event is the roofing system, particularly a commercial building with a low-slope condition. Damage or failure to the roofing membrane is not only problematic in its own right, but it also exposes other parts of the building, equipment, critical building systems, and the people inside to the ravages of weather events. Consider that during severe weather, the roof could be exposed to high winds, hail, accidental puncture, unusual snow loads, or intense UV exposure from the sun, all of which could compromise the protective barrier that the roofing is meant to provide. With the short-term and long-term integrity of the building at stake, not to mention human safety, the roofing requires some special attention.

Commercial roofing systems need to address many details and conditions to be fully protective and resilient, but the fundamental decision needs to be made on what type of roofing membrane to use. One of the more popular and cost-effective systems, namely EPDM, has also been shown to be quite durable and resilient if specified and installed properly. With more than 15 billion square feet of membrane installed across the globe since the 1960s, EPDM has an impressive history of performance in the commercial roofing industry. Numerous EPDM roofs installed in the 1980s have been documented to be still performing well over 30 years later, a fact that positions EPDM as one of the strongest and most durable single-ply membranes available. While EPDM has exhibited strong physical characteristics since its inception, it has also undergone many technological advances. Some of these developments include factory-applied seam tape, providing improved seam quality and a quicker application, plus a variety of pressure-sensitive, prefabricated accessories. A particular advancement for resiliency and durability is the introduction of 90-mil membranes and 75-mil reinforced membranes in addition to the standard offerings of 45- and 60-mil membranes. All of these advances have improved the life-cycle performance, resiliency, energy savings, and installation efficiency of EPDM membranes. Manufacturers have recognized this improved performance and can now offer 30-year total system warranties on their installations as well as a 40-year nonprorated warranty option for the material alone.

Some of the defining characteristics that need to be specified for a resilient, high-performance roofing system are as follows.

• Membrane: Thicker and more durable 90-mil EPDM, 75-mil reinforced EPDM, or 145-mil EPDM with special fleece backings are available.
• Splices: Six-inch-wide splice tape for added peel, shear, and water resistance compared to the typical 3-inch splice tape. Six-inch factory-applied tape greatly exceeds the peel and shear strength of hand-applied seams while delivering a permanent, watertight bond. A seam applied in a controlled factory environment is a tremendous advantage that enhances workmanship.
• Flashings: All critical flashing details should be double wrapped with 90 mils of pressure-sensitive flashing.
• Detailing: Lap sealant needs to be applied to the exposed edge of all seams, flashings, and joints.
• Adhesives: Standard and low-VOC solvent-based bonding adhesives must be properly applied per manufacturer and industry standards.
• Cover boards: Usually a minimum ½-inch-thick rigid cover boards should be installed.
• Insulation: Coated glass facing versus standard paper faced polyiso, upgraded to 25 psi.
• Fastening density: Increased to one fastener per 2 square feet in lieu of the typical one fastener per 4 square feet.
• Insulation adhesive density: Increased to 4 inches on center in the perimeter and 6 inches on center in the field.
• Perimeter securement: Six inches on center attachment compared to the typical 12 inches on center.
• Metal edging: Engineered systems with high-performance values.

By paying attention to these details, every critical component of a 30-year EPDM roofing system is enhanced to deliver the optimum resiliency performance when the time comes that it is needed the most. Samir Ibrahim, director of design services at Carlisle SynTec, has seen first-hand the notable increase in performance of such systems. “EPDM thermoset roofing membranes feature superior UV and heat resistance along with excellent hail resistance,” he says. “Ninety-mil EPDM is thicker, more durable, and the basis of design for 30-year warranty roofing systems. The end results are that EPDM roofing systems can be designed to handle Mother Nature’s worst, whether it be 100-mph winds and driving rain, 2-inch-diameter hail, unusual snow loads, or intense UV/heat exposure.”

Photos courtesy of Carlisle SynTec Systems

The Wausau, Wisconsin, middle school and high school employed high-performance EPDM roofing for long-term durability and resiliency while achieving very favorable life-cycle costs.

Seismic Resilience

While many threats to a building come from above, seismic activity in the form of an earthquake comes from the ground below. Hence, the design of a building foundation and everything around it becomes important to address resilience and safety when seismic events occur. Toward that end, an engineering technique known as base isolation has been developed and used across the Pacific Rim, including the United States. This technique recognizes that if a building is constructed in a conventional manner, its base (i.e., foundation) is directly connected to the surrounding earth. During an earthquake, that connection will cause the building to move right along with the earth and potentially sustain extensive damage as a result. The isolated base approach disconnects the transfer of seismic forces in the earth from the building by resting the foundation on flexible bearings or pads known as base isolators. The isolators work much the same way an automotive suspension system does when a car encounters a bumpy road and absorbs the shock. In the same way, the base-isolation system absorbs the earthquake movement instead of the building. That means this system can make buildings that are otherwise vulnerable to earthquake damage, such as medium-rise masonry (stone or brick) or reinforced concrete structures, safer and more capable of withstanding earthquakes. Engineers who use it do point out that it of course is not suitable for all types of structures and works best in hard, not soft, soils.

In conjunction with base isolation and other seismic mitigation measures, seismic expansion joints are also needed, particularly for larger buildings. The purpose of these joints is to separate different parts of the building from each other or to separate outdoor areas that are connected to the ground (i.e., patios, plazas, roadways, parking structures) from base-isolated buildings and structures. It is common to use expansion joints for thermal movement in buildings, and the techniques and finish options for that are well known. Seismic expansion joints pose a larger challenge in that both sides of the joint will not only be moving suddenly and dramatically, but they also need to be designed to allow a much greater moving distance. Seismic expansion joints on the order of 12 inches, 24 inches, or even 30 inches are not unusual. The design issue becomes bridging that gap to make a building or site surface usable during the majority of time that earthquake forces aren’t being imposed.

In response to this situation, manufacturers have developed some very sophisticated expansion joint cover products that can aid in the functionality of a building before, during, and after a natural disaster, such as an earthquake. The cover is basically a structural (i.e., walkable or drivable) surface that can span the gaps formed by the seismic joints. During a seismic event, some covers are designed to pop up out of the way, allow for the movement going on in the ground, and then return back into place once the seismic movement ends. That means that these covers are not intended to be sacrificial and therefore require minimal repair after a movement event. Because of the ability to return back to its resting position after an earthquake, it also eliminates the concern that the cover might block egress areas or cause tripping hazards.

Manufacturers of such expansion joint covers understand that there are many unique project situations and therefore offer a range of standard choices and will often work with architects on custom-designed solutions as well. Large joints or moat covers are available that are designed to accommodate base-isolated buildings in seismic zones. These covers surround the perimeter of the base-isolated building and, during a seismic event, they too will pop up out of the ground and return to their place after the event. Some seismic expansion joint cover systems have center pans that are strong enough to be filled with surrounding floor or wall finishes, which minimizes the cover’s sightlines for an aesthetically pleasing look. For example, a seismic moat cover system can accept concrete or terrazzo so that it blends in with the sidewalk or surfaces that typically surround a building. In other cases, expansion joint covers will span across areas where vehicular loads travel on a daily basis, imposing heavy and frequent loads. The good news here is that yes, some cover systems can handle these heavy loads, but it is important to notify the expansion joint cover manufacturer of the kind of loads that will be crossing over the cover so it can ensure that the proper heavy-duty cover is selected and installed.

Gabe Blasi, CSI, CDT, is the senior general manager with Construction Specialties. He points out that “expansion joint cover manufacturers work closely with architects, engineers, and facility owners to provide attractive, proven products that augment the seismic performance and resilience of buildings.” It behooves design teams, then, to consult with these companies to understand the options and capabilities of the available products so that the best choices can be made for specific building conditions.

Images courtesy of Construction Specialties

The seismic expansion joint cover system shown on the left is designed to handle everyday thermal expansion and contraction, as well as seismic movement in which the center pan pops up when the joint opening narrows and settles back into place after a seismic event. The photo on the right shows moat covers incorporated into the sidewalk surrounding the Zuckerberg San Francisco General Hospital and Trauma Center. Because the moat cover pans can accept matching floor materials, the covers integrate seamlessly into the sidewalk.