Feature Metal Roof Retrofits Stretching your dollars to last for decades By Chuck Howard, PE R etrofitting flat roofs with sloped metal assemblies is a concept becoming particularly salient during these tough economic times. However, there are benefits beyond cost savings. Interestingly, of the 3.7 billion m2 (40 billion sf) of roofing annually installed in the United States, only a fraction of that amount entails retrofitting roofs with sloped metal systems. Yet, replacement and repair continues to account for approximately 75 per cent of all roofing work, and various industry sources suggested some 2.8 billion m2 (30 billion sf) of roofs needed major repairs during 2009. In Canada, the situation is quite similar. Adding slope to an existing flat roof can generate a strong return on investment (ROI) in the form of lower energy costs and little or no maintenance for decades. In most circumstances, this can be accomplished without having to remove the existing flat roof. A slope as low as 6.4 mm (¼ in.) per foot is sufficient to satisfy most metal roof warranties and can be achieved by installing lightgauge steel columns in varying lengths. After variable height columns are installed, the steel purlins are positioned between each column and the necessary bracing is installed. A new metal-standing seam roof panel system is then placed on top of this sub-framing system. When the job is complete, it is like having a small metal building sitting on the original roof. Lasting for years If properly maintained, the exterior surface should last at least 30 to 50 years. The exterior surface, whether painted or bare, can reflect up to approximately 80 per cent of solar energy that would normally penetrate the building. Adding unfaced fibreglass insulation in the newly created cavity can further increase the building’s ability to conserve energy used to control temperatures in interior spaces. In today’s market, the cost of adding a sloped metal roof system over an existing roof is usually less than the price tag associated with removing a flat roof, transporting the removed materials to a landfill, and replacing it with built-up roofing (BUR) or modified bitumen (mod-bit) roofing with tapered insulation. (The insulation is required by most code authorities to achieve a certain level of roof slope.) 50 January 2010 Construction Canada CC_JanFeb10.indd 50 12/22/09 11:56:18 AM Photos courtesy The Metal Initiative