How to Select Roofing Systems

Roofs should be viewed as a system, not just as individual products. This is the best way to get the right roof system for your particular building.

Remember when you were a kid making a sandwich out of the bread available, with all the fillings you could find with a pickle from a jar to top it off. The same used to apply to roofs. In the past, roofers meant taking the cheapest insulation, adding some generic asphalt to the most readily available felts and covering them with gravel. As the industry matures, the method of grasping and using the roof structure is all but finished. Instead, roofs are designed as systems, a complex undertaking designed to ensure that the finished roof meets a number of requirements. It is important for facility managers planning a new roof to understand the various factors that need to be considered.

The starting point on the way to the system design was the fire class. After a devastating fire leveled an automobile plant, Factory Mutual Insurance (now known as FM Global) began investigating how roof components were contributing to the spread of the fire. This led to tests for flame spread and other problems with most building materials and products that interact directly with people. Companies like UL, FM Global, and Warnock Hersey have tested A, B, or C products and ratings. Roofs were tested as a system and only certain components in that particular order would qualify for fire class.


Another step towards system design was the introduction of guarantees. Manufacturers have determined which materials can be used in a guaranteed system so that the materials are compatible and meet the manufacturer’s standards.

System design became even more important as manufacturers developed new and innovative roof membranes – single layers, modified bitumen, liquid applied – and the range of installation methods expanded to include methods other than fully adherent. The dizzying number of new roof options led to an increased use of consultants with specialist knowledge of roof systems. As restricting the roof components to one manufacturer helped ensure that the materials were compatible and therefore more likely to have a better roof, a systems approach became more common.

Code requirements

The next big shift in designing systems rather than individual components came in response to a little storm called Andrew. This incredibly devastating hurricane undoubtedly demonstrated how little the construction industry in general, and roofing in particular, did to mitigate storm damage. This prompted Miami Dade County, where the damage was worst, to reevaluate how roofs were designed and installed. According to Michael Goolsby, Division Head II, Regulatory and Economic Resources, Miami Dade County, the code has been revisited for improved public safety. This led to what Goolsby calls “performance through compliance”.

Previously, contractors or design professionals were responsible for ensuring that the products they selected met the code requirements. This major revision of the code continued to require testing of each material to meet recognized standards (such as ASTM). However, it was added that all individual components of the roof system had to be tested as a unit and the entire unit had to meet the requirements of more stringent standards for design, material testing (existing or newly developed) and certification of testing laboratories. In other words, the roof manufacturers had to test the systems as a whole. “When you exchange products, you don’t know if the tests are still valid,” says Goolsby.

The drainage requirements have also been revised so that a ¼ inch slope is the minimum. This meant a change in the design of the insulation. Roof manufacturers have added sloping insulation to their system designs in order to do justice to the parameters.

This was the beginning of roofing as a science as the emphasis was on calculating wind lifts, drainage areas and attachments for air conditioning. Architects and engineers were required to perform signed and sealed calculations before approvals were issued to ensure that the specified materials conformed to the code. With fire protection regulations, wind lift calculations and product approvals as well as the requirements for building construction and property, the roof construction became even more complex and technically complex. The better contractors realized that their liability in the roofing process was reduced by leaving the roof construction to the consultants. If they followed the specifications exactly, they could not be held responsible for design errors.

According to Deborah Costantini, senior architect at Hoffmann Architects, the codes now need to be analyzed on the roof terrace to see if it will be used as the building’s membrane and to see if it will act as a fixture. “This requires you to look over the ceiling, but it’s not always possible,” she says. “You have to move a lot more from the rooftop to see what is code and what is not. You also have to study engineers, which makes it a lot more difficult. “The result of the analysis can mean anything from adding fasteners to replacing the deck to meet the requirements.


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