By Rodger Russ and Chris Ripley
When building owners were surveyed in a 2005 study commissioned by Ducker Research Company, the most important criteria for choosing roofing materials, they ranked service life and lifecycle cost first and second, while initial cost came in second-last (i.e. ninth place).1
The findings on the lifecycle costs of low-slope roofing cut across the three major roofing material categories: metal, asphalt, and single-ply. The clear message is building owners are looking for the same things in roofing—a system that lasts for many years and saves money over the long term.
Experience demonstrates a building’s roof system can account for 10 per cent of total construction costs, but up to 60 per cent of lifecycle maintenance costs. Of course, the lifecycle costs of roofing go beyond material and maintenance. Broadly speaking, the choice of a roofing system impacts energy consumption in categories including:
- heating and cooling;
- feasibility of roof-mounted renewable energy; and
- the building’s market value.
Research and product testing, combined with in-the-field experience spanning four decades, make a strong case for high-quality, standing-seam metal roof systems. This is based on durability, low maintenance cost, and adaptability to current trends driving energy efficiency and sustainability in the commercial building sector.
What owners report
The study drew from case studies involving 36 roofing assemblies, covering office, retail, institutional, and warehouse/industrial buildings to include an equal number of 12 metal, asphalt, and single-ply roofs, averaging 8547 m2 (92,000 sf).
Another Ducker study, analyzed overall life expectancy. It found metal roofs had an expected service life of 40 years, versus 23 years for asphalt and 20 years for single-ply. Using this information, the 2005 study placed the annual lifecycle cost of metal roofs at approximately 30 cents per 0.09 m2 (1 sf), compared with 37 cents for asphalt and 57 cents for single-ply, based on expected service life.
Owners reported spending 3.5 per cent of total installation costs on maintenance for metal roofs, versus 28.5 per cent for asphalt, and 19 per cent for single-ply over the expected service life.
Inherent qualities of metal roofs help account for these differences. Today’s standing-seam metal roof systems are proven to deliver weathertight performance for at least 40 years. The roof acts as a monolithic steel surface covering the entire building.
The study found leaks occurring in metal roofs were mostly due improper maintenance, rather than the materials used. When specifying metal roofs to improve performance, architects should recommend metal roof systems with concealed fasteners.
Metal roof attributes
The components of metal roofs can include:
- roof clips that securely hold the panels to the structural members, with enough flexibility to allow movement with expansion and contraction caused by daily and seasonal temperature changes;
- weathertight sealing, with 180 degrees of the roof panel seam field-rolled to complete a 360-degree double-lock seam, also impregnated with sealant;
- factory-punching to ensure proper alignment of the roof panels, paired with heavy-duty fasteners;
- splices staggered to prevent exposed seams and leak points located directly over supporting steel to withstand foot traffic and snow loads;
- steel-rod bracing that neither stretches nor sags—this allows the roof to retain its original strength and tightness; and
- roof curbs and openings engineered at the factory and fasteners concealed inside the curbs to eliminate leaks.
These metal roofs in many cases can be applied directly over aging asphalt, single-ply, or existing metal roofs to restore weathertight conditions and provide long-term building protection. To ensure metal roof systems can accommodate the extra load, it is prudent to consult a structural engineer to review the existing structure.