Metal roofing and lifecycle thinking

by mdoyle | September 1, 2013 12:10 pm

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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[2]

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;
• lighting;
• 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.

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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.

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Conserving energy
Although durability and low maintenance help keep long-term costs down, a sound roof design also helps conserve energy and generate substantial savings over a building’s life. As part of a tested assembly, a quality standing-seam roof system can result in energy savings.

Energy efficiency in buildings is not just desirable, it is also becoming mandatory with more stringent building and energy codes. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, most recently revised in 2010, signals a new era of accountability for building efficiency. Additionally, the release of the 2011 National Energy Code of Canada for Buildings (NECB) also follows a similar path of increased energy conservation and code compliance, including prescriptive requirements for insulation, building envelope, and assemblies.

The roof is often the least energy-efficient part of the building envelope. Heating and cooling typically consume about one-third of a building’s energy, and half of that results from heated or cooled air lost through the roof. A well-designed and properly installed roof helps reduce those losses and maintain more consistent interior temperatures.

Thicker insulation is part of the answer. However, when applied to conventional built-up roofs (BURs), the added insulation may negate the energy savings by speeding deterioration of the roof surface. Metal roofs, on the other hand, can accommodate more insulation—up to an R-value of 40 with no effect on roof service life.

Metal roofing assemblies are available that have achieved these values through testing to meet code requirements. Guarded Hot Box for U-factor tests assess and validate insulated roof and wall systems to determine actual thermal performance are proven compliant with the ASHRAE standard.

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Cool roofing
Metal systems can also function as cool roofs, helping owners save money by repelling, rather than absorbing, the sun’s heat during summer and reducing air-conditioning costs.

Roofs painted in light colours reflect more solar radiation and reduce the roof temperature. Newly developed infrared (IR)-reflective pigments enable roofs to reflect significant sunlight even when darker paints are used. Additionally, on cloudy days or after sunset, metal roofs give up their heat faster than other roofing materials.

Cool metal roofs perform well even when compared with white membrane roofing. A study at the Oak Ridge National Laboratory (ORNL) in Tennessee found a metal roof more effective than conventional roofs in reflecting the sun’s rays and in preventing solar heat transfer into a building.²[7] In Canada, cool roofs that have high reflectivity and low-emissivity (low-e) reduce summer cooling loads. Additionally, cool roofs help in the winter by retaining heat and as a result reducing heating load.

Also, cool roofs have the added benefit of mitigating the urban heat island effect, helping reduce smog formed from the reaction of nitrogen oxides and volatile organic chemical compounds (VOCs).

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Savings on lighting
Energy savings from metal roofing go beyond cooling and heating. Today’s systems, like their asphalt and single-ply counterparts, can accommodate the roof-mounted daylighting technologies. Renewable energy plays a growing role in buildings, and the potential for rooftop renewables is great. Whether for thermal energy or electricity, quality metal roofs accommodate solar panels without requiring penetrations that could compromise roof integrity.

Electricity for lighting can be a building’s largest operating expense. Consequently, new building energy-efficiency codes and standards call for daylighting in buildings above specified square footage and height and in certain usage categories, such as such as ASHRAE 90.1. Beyond creating more pleasant work conditions, daylighting can significantly reduce energy usage.

Skylights and other roof-installed devices can strongly contribute to daylighting. A study, Commercial Building Toplighting: Energy Saving Potential and Potential Paths Forward,

found an economically optimal toplighting system (i.e. skylights with electronic lighting controls to turn off electric lights when not needed) saved 35 to 55 per cent of annual lighting energy, with smaller impacts on heating and cooling energy. Depending on climate and building type, the same study determined toplighting could annually save 11 to 32 cents per 0.9 m² (1 sf).

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Some of the latest daylighting devices have marked advantages over traditional flat skylights. These domed units have prismatic embossing that collects up to three times more of the sun’s rays earlier and later in the day, when the sun angle is low. Prisms refract sunlight into microbeams that transmit more light into the building, without glare, hot spots, or ultraviolet (UV) damage. The devices have been shown to reduce electric lighting costs when integrated with lighting controls—providing a return on investment (ROI) in as little as three to five years.

The units can reduce the number of total roof penetrations by 30 per cent due to their higher light transmittance. A self-curbing design avoids the inherent risk of leaks around flashings found in the traditional curbs used on conventional skylights. The system is integrated into the metal panel seams to minimize the amount of contact with water flow overall.

Types of metal used in standing-seam metal roof systems primarily include painted galvanized steel, aluminum-zinc alloy coated sheet steel, and bare aluminum. Beyond esthetics, one type of metal might be specified over another because of price, service life, lifecycle cost, or manufacturing offering.

Conclusion
Roofs that improve buildings’ energy performance can not only save on monthly utility bills but also help buildings command higher rents and selling prices. Markets are taking notice energy-efficient buildings carry economic advantages. For example, studies show rent premiums for Energy Star-certified office buildings can range from five to 8.5 per cent, while resale premiums for such buildings can range from 13 to 26 per cent.

High-quality metal roofing systems can add value to building and renovations on many levels from longevity and weather protection, to energy code compliance, operational savings, carbon emission reduction, and enhanced occupant comfort.

Notes
¹ For more detailed information about the study and its results, visit www.themetalinitiative.com/content/building_with_metal/benefits/costefficiency/ce_lifecyclecosting_analysis.cfm[10]. (back to top[11])
² For more, see the study at www.mbma.com/display.cfm?p=30&pp=24&ppp=12[12]. (back to top[13])

[14]Rodger Russ is the North American sales manager for the roof division of Butler Manufacturing. He has more than 27 years of diverse experience since starting in the sheet metal trade in Chicago. Russ has worked for multiple manufacturers in various roles, including product development, training, product and sales management, and consulting. In his role with Butler, he focuses on applying new solutions for the retrofit segment of the metal roofing market. Russ can be contacted via e-mail at raruss@butlermfg.com[15].

[16]Chris Ripley is the regional sales manager for Butler Buildings Canada. He previously served as an area manager in Ontario and worked for an Ontario ‘Butler builder’ for 17 years. Ripley has nearly 30 years of experience in the construction industry. He can be reached at caripley@butlermfg.com[17].

Source URL: https://www.constructioncanada.net/metal-roofing-and-lifecycle-thinking/

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