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1. Building code requirements There are currently more than 40,000 building codes across the United States. Although the majority are based on the International Building Code (IBC), some local jurisdictions enforce stricter standards to address regional concerns. Designers will always have to take into consideration any additional mandates prescribed by local jurisdictions.
The non-continuous attachment of metal roofs makes them particularly susceptible to wind uplift. The major factors relevant to a roof’s ability to withstand these pressures include:
American Society of Civil Engineers (ASCE) 7 provides a methodology for calculating the relative force exerted on a particular roof when subjected to the anticipated wind uplift pressures. 3. Value engineering In the realm of roof performance, reducing up-front costs for short-term savings inevitably leads to higher costs and liability down the road. Learning to analyze the bottom-line benefits of rooftop longevity is critical to specifying appropriate metal solutions. The performance-to-cost ratio varies with every roof specified, and can only be identified through a comprehensive review. 4. Lifecycle cost analysis Lifecycle cost analysis (LCA) is a worthwhile exercise when attempting to establish the value of metal systems in comparison with non-metal alternatives. ASTM E 917, Standard Practice for Measuring Lifecycle Costs of Buildings and Building Systems, is a uniform procedure for establishing lifecycle costs for all types of roofing. All anticipated costs over the working life of a roof are added to the initial material and installation costs to arrive at a realistic total cost. 5. R-value The roof’s principal function is to protect the insulation — and everything else under it — from water damage. The critical measurement for determining the effectiveness of a roof’s insulation is the R-value, which measures how well a particular material resists heat transfer. Since wet insulation is typically considered to have an R-value of zero, once a roof develops leaks that reach the insulation, the owner’s R-value investment is virtually lost. 6. Energy payback Emissivity (radiated heat) is related primarily to the roofing material, and in the case of metal roofing, the coatings used increase savings through reflectivity. 7. Fire resistance
The IBC mandates that metal roof systems meet the testing standards of one of two similar protocols:
8. Condensation Typically, condensation occurs when humid air comes in contact with a cold surface. In the context of the building envelope, there are several circumstances likely to "precipitate" potentially damaging condensation, such as:
Despite its natural susceptibility to corrosion, metal is suitable for all the aforementioned conditions, provided proper insulation and ventilation or vapor retarders are installed. Although metals have a greater propensity towards condensation, a properly installed metal roof system should be condensation-free. 9. Indoor air quality Moisture penetration through roofing and walls is a major source of mold-breeding moisture that can infiltrate ceiling tiles, carpets, furniture, and HVAC systems. Increased public awareness of the dangers of airborne mold makes leak prevention a critical priority, particularly when specifying roofing for public facilities. Properly installed high-performance metal roof and wall systems equipped with appropriate ventilation and/or vapor retarders can eliminate the water penetration and health hazards associated with airborne mold. 10. Snow/ice retention In many regions, it is imperative the roof be designed to accommodate the added load of built up snow and ice, and to safely allow them to leave the surface. Interestingly, snow and ice tend to sit on a sloped roof just as they would on a less steep surface; that is, until melting commences, when they become a grave danger to people or property below. In Conclusion Today’s trend for sustainable designs that reduce environmental impact is helping drive the metal roofing market to new heights. Understanding the engineering concerns fundamental to the proper design of metal roofing will enable architects, engineers, and specifiers to take advantage of these systems while serving the long-term interests of their clients.
Mike Huber, PE, has been a professional engineer for the last 12 years. He is also presenter of an American Institute of Architects (AIA) accredited course on the engineering and design of metal roof systems. To request an onsite AIA accredited presentation about metal roofing, e-mail your request to learn@imetco.com. © Copyright 2006, Innovative Metals Company, Inc. | |||
For more information on this topic, please call IMETCO at 800-646-3826 or send an e-mail to learn@imetco.com. | ||||
 Neither Innovative Metals Company, Inc. (IMETCO) nor any of its affiliates makes any representation or warranty of any kind with respect to the materials and information contained herein. Although IMETCO attempts to provide accurate information, this bulletin is intended for general reference and informational purposes only. IMETCO assumes no responsibility for errors or omissions in the content contained in, or directly accessible from, this bulletin, and makes no commitment to update such information. IMETCO shall not be liable for any damages relating to your use of, or reliance upon, this bulletin or any of its content. | ||||
When it comes to designing or specifying commercial metal roofing, knowledge is power. This article breaks down 10 fundamental areas to consider when designing with metal roofing. Although the particulars vary according to geographical region, system profiles used, and the characteristics of each building, an awareness of the principles underlying each of these areas is a valuable tool for design professionals.
2. Wind uplift 
Unlike roofing materials derived from asphalt or rubber, metal roof substrates are naturally resistant to fire. Additionally, hot metals will not emit noxious gases to create the additional health and safety hazards associated with some other materials.
