Perimeter metal attachment should be determined through the completion of a perimeter edge calculation. This calculation determines the proper securement spacing required to meet the wind design pressure of an existing building. In high-velocity wind zones, the base perimeter materials should be secured to the structural components - not the deck - with properly approved fasteners. The perimeter metal materials must comply with ANSI ES-1 regulations, which require testing and certification of the materials.
Federal regulators allowed for a phasing out period of CCA for nearly two years, up until 2006, and until then most lumber treated in the United States still used CCA. This was partially due to the fact that viable alternatives were not readily available. The lumber producers are currently using two newer additives - alkaline copper quat (ACQ) and acid copper chromate (ACC). Both of these products have a short track record and are largely unproven in this area. This could lead to the instability that we have seen with other roofing products that have changed their basic formulations over the years. Failures at this component due to moisture deterioration such as wood rot or termites (a significant concern in the South) could potentially weaken the roof at its most vulnerable point.
Since most roof damage from high-velocity winds occurs at the perimeter edge, a metal blocking system has been developed to enhance the roof’s perimeter for wind uplift resistance. The Alternative Roof Blocking System (ARBS) is an engineered metal fabrication system that was developed and patented by Henry Gembala. The materials used for the manufacturing of the ARBS System are constructed from materials meeting the standards, quality and thickness recommended by SMACNA, NRCA, IBC and ASCE 7. The blocking assembly includes one or more pre-formed component structures fabricated from a non-corrosive, durable material. The blocking can be fabricated from galvanized steel, aluminum or stainless steel, depending on project requirements.
The major advantage of the system is the enhancement of wind uplift protection that it provides at the roof’s most vulnerable point - the roof edge. The metal edge material is specifically designed to meet wind uplift pullout and pullover tests. Tests completed by an independent testing agency (Hurricane Test Laboratory) on the edge blocking indicated that the system performs better than traditional blocking methods. HTL tested five edge blocking systems to failure as defined by Florida Building Code TAS 111B. The average failure load for all specimens was 755,000 foot-pounds with a standard deviation of 51.23 foot-pounds, which correlates to a pressure of 862.85 psf.
The blocking system is prefabricated and formed to fit any thickness of lightweight concrete or insulation - including tapered insulation. The blocking is properly formed to the slope of the lightweight or tapered insulation. On lightweight concrete systems, the blocking is secured directly to the lightweight concrete and prefabricated vent holes are set at the intermediate portion of the blocking to provide for venting of gases and moisture that may accumulate in the roof system, thereby reducing the likelihood of premature roof failure.
Finally, metal blocking is less expensive per linear foot than lumber, and since the cleat is built into the blocking system, application of edge metal and coping is seamless and is less labor intensive. The blocking system can be formed on-site, allowing the contractor to have the material shipped in coils to the jobsite. This eliminates contractors from having to turn their jobsites or shops into lumberyards for each project.
ARBS provides a Quality Assurance Certificate (upon request) that includes the data from the specific lot of material referenced and an assurance to quality in the materials and manufacturing process. ARBS also offers a warranty on all of its manufactured components that is consistent with the terms and materials offered by the roof membrane manufacturer used on the project.