Endurace/Longevity of Roofing Systems
Many factors affecting the durability and longevity of roofing systems are beyond our control, such as climate, catastrophic accidents and violent storms. In terms of High-Performance Roofing, endurance is the ultimate reflection of the performance of every roofing component or element that can be controlled by intelligent design, manufacture, installation, and maintenance, including:
- Proper design for the location, climate, roof deck and type of building.
- The type of roof deck matched to the insulation/membrane systems.
- Proper drainage to prevent ponding water. Many experts believe this to be the most important factor affecting longevity.
- Professional workmanship during installation that is well supervised and inspected.
- Physical properties over time of the system selected, including: solar reflectance and emittance, tensile strength, water absorption, fire resistance, wind uplift, elongation and thermal expansion, dynamic puncture resistance and resistance to rooftop contaminants such as acid rain and air pollution.
- Flashing details used around roof penetrations, walls and curbs – where many difficulties arise.
- Inspection and maintenance on a regular basis. This includes limiting the access and traffic on the roof.
- Accountability of the manufacturer and/or roofing contractor for the entire roofing system under one warranty (versus partial systems with several warranties).
Most green building experts believe that longevity is among the most important factors contributing to the sustainability of any building product, including roofing systems. Long-lasting roofs reduce the rate of landfill waste buildup, as well as the demand for re-roofing projects, with all of the embedded energy that entails.
Every year of useful service free of major maintenance and repair work also reduces the life-cycle cost of any roof, which is covered in the next section. According to the survey funded by The Roofing Industry Alliance for Progress in 2005, the average life expectancy of a low-slope roof is 17 years. In January of 2006, Roofing, Siding and Insulation magazine reported a “national average for roof service life” of 12 years. In his book, Roofing Failures, acknowledged roofing technology authority Carl Cash estimated the average service life of specific types of roofing systems, ranging between 12.1 years for spray polyurethane foam to 16.7 years for a five-ply BUR system.
More importantly in terms of High-Performance Roofing, Cash suggested that building owners consider the durability range of various systems, a better indication of how long the best roofing systems in each category can be expected to last. By this measure, five types of roofing systems have a high-end range of service longer than 20 years: PVC thermoplastic single-ply, asphalt-glass fiber BUR, SBS polymer-modified asphalt, EPDM thermoset single-ply, and asphalt-organic felt BUR.
Roofing Endurance and Failure
After analyzing more than 1,500 roofing failures, Carl Cash concluded that there is no accurate means of predicting the longevity of any specific roof, but there are ways of maximizing the potential for a long-lasting roof. Anyone interested in a High-Performance Roof should consider his four guidelines for roofing endurance:
- Peer review of the contract document before bidding by a specialist in roofing technology with no financial interest in the project can eliminate one-third of the problems experienced with roofing systems.
- Use roofing systems, manufacturers, designers and contractors with long, successful track records.
- Use monitors hired by the owner to oversee the installation. Defective workmanship accounts for between 30 percent (Cash) and 47 percent (NRCA) of roofing failures. Another way of ensuring proper installation is to use suppliers that train their contractors and inspect every roofing job shortly after completion.
- Buy competence, not price, in the supplier, designer and contractor. Building owners should consider long-term value rather than up-front installed costs.
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