SAFLOK 700 – Value Engineering at Work
Today's drive to design buildings that reduce environmental impact is helping drive the metal roofing market to new heights.
Most large roofs are concealed fix roof systems (also called secret fix systems). In principle, they provide some common benefits:
The sheet is fixed to the purlin with a clip system. The sheet hides the clips completely, providing a neat, watertight and no-holes roof, which eliminates the risk of leaks.
Metal expands and contracts at about 1mm per 1m. The clips allow the sheet to thermally expand over the clip in a sliding movement, so very long lengths of continuous sheeting can be installed with no end laps, thus providing further weather tightness.
However, the secret from a performance point of view is not that the sheet is secured by an unseen clip, but the engineering of the clip, and its fit with the profile of the sheet. Aside from profile itself, it is the clip designs that distinguish concealed fix metal roofing systems from each other.
One of the biggest dangers with concealed fix roofing is the wind-uplift performance. No two roofs are the same, and most roofs experience several different areas of wind pressure, whether negative or positive pressure. The material thickness of the clip (gauge) helps determine its inherent strength, which in turn helps to determine the minimum wind-uplift resistance requirements for a particular roof.
For all roofing systems, energy payback is derived almost exclusively from R-value, and R-value is derived almost exclusively from insulation. A high-performance metal roofing solution is among the best ways to protect that investment. Once a customer understands how much of his R-value investment is lost, once water penetrates the insulation, the added protection provided from a high-performance roof becomes apparent.
In the realm of roof performance, reducing up-front costs for short-term savings inevitably leads to increasing costs and liability down the road. Learning to analyze the bottom-line benefits of rooftop longevity is critical to specifying appropriate metal roofing solutions. The performance-to-cost ratio will vary with every roof specified, and can only be identified through a comprehensive review of several factors, including:
- How long will the client own the property? Since metal roof systems can significantly outlast most non-metal alternatives, property owners who intend to hold on to their buildings longer will reap the largest rewards from metal's life-cycle costing advantages.
- How disruptive will eventual restoration and re-roofing be to the building's occupants? The installation of a metal roof is odor-free, cleaner, and more environmentally friendly than hot-applied systems. However, installing metal systems can present logistical concerns, especially for high-rise buildings with limited access. Although freight elevators can typically carry materials needed for non-metal systems, for metal systems, large cranes may be necessary to haul longer panels to the top of the building.
- What is the intrinsic value of the property under the roof? The higher the value of the property occupying a building, the easier it is for building owners to rationalize the higher initial costs of metal systems.
- What is the customer's existing budget? If price were no object, we'd all be living and working under roofs of copper, zinc, or even titanium. Regardless of the desirability of long-term solutions, short-term budget realities sometimes prohibit lasting solutions. When a customer's initial budget will not accommodate the costs of a premium metal, innovative financial products such as leasing may be considered. Equally relevant is how soon additional money will become available. It may make sense to install a low-cost alternative on new construction, when budgets are strained, if seven years down the road money will become available for installing a more lasting metal roof system.
- How important are aesthetic considerations, given the roof's location and the building's function? Aesthetic versatility is probably the single biggest reason that owners opt for metal roofing. When aesthetics are a major concern, metal roofing offers added value.
- How likely is it that the owner will follow through on routine maintenance? Generally speaking, metal roofing requires less maintenance than non-metal systems, which may need more frequent re-coating, fresh graveling, or aggressive restoration to maintain resistance to ultraviolet (UV) radiation and weather.
- How frequently will the roof need to be accessed due to HVAC, rooftop photovoltaic (PV) systems, or other utilities? Although metal systems withstand foot traffic as well or better than non-metal roofs, roofs that require a lot of penetrations for HVAC or other appliances are not ideal candidates for metal roofing, as previously explained (see introductory section of this article on the advantages of metal).