Proper Specifications Lead to Successful Metal Roofing Systems
When designing a metal roofing system, the multiple choices in profiles have kept up with the increasing demand, and Section 07 41 13 in MasterFormat has become crowded with all the various options available.
Starting with the submittals, you can enhance the quality of the work with a set of manufacturer’s shop drawings and a pre-construction meeting to review details, installation and the basic sequence of work.
Is the installer trained by the manufacturer or have they completed the Metal Roof Installation Certification program through the Metal Construction Association (MCA)? This simple upfront quality assurance step can save you thousands of issues arise down the road and will build confidence in the project team from the beginning. Have the perimeter edge flashing details been tested to the ANSI/MCA FTS-1-2019 standard to exceed the project design pressures? Failure of metal perimeter edge flashings is often cited as a leading cause of all roof system failures. This new standard, developed by the MCA, has been proposed to become part of code, like the ES-1 standard for coping. The ANSI/MCA FTS-1-2019 was approved by ANSI on June 25, 2019 and testing is available now.
For the base metal or substrate, aluminum, steel and natural metals like zinc and copper are still the most prevalent, and determining the base metal is the logical place to begin. Each holds it advantages: aluminum has a strong barrier resistance, steel has a strong strength-to-weight ratio, and the aesthetics of a zinc or copper patina are a sight that can last hundreds of years.
Always include references to your building codes, state and local requirements, and any sustainability programs. For an aluminum roof panel, reference ASTM E 1637, for steel panels, it is ASTM 1514.
Are we designing a functional low-slope hydrostatic system or an architectural steep-slope, water-shedding, hydrokinetic system? Again, each has its advantages. In its proper place, you can ensure the performance for the life cycle of the building.
Is the seaming method doable in the real world? Anyone who has lugged a 150-pound seamer up a chicken ladder on a 12:12 slope knows how it can mar the finish. Follow the same logic with your desired finish. Ask any paint supplier, the pretreatment is the critical first step. It improves the surface reactivity, promotes paint adhesion, and can provide enhanced corrosion resistance. Painted metal panels with a 70% PVDF have proven they can hold most of the original color over time.
Will solar panels be installed on your roof? Standing seam metal roofing is the perfect platform over which to install solar panels, due to its long service life. When installing a crystalline system (typically warranted for 25 years of power generation), a building owner benefits from a roofing substrate that has a greater life expectancy than the solar panels. Solar panels can be attached to the seams of the metal roofing with specially designed clamps, avoiding roof penetrations. As well, highly reflective roofs with cooler rooftop temperatures result in better performance of solar panels.
That brings us to the panel. Once you check the boxes prior, it all starts to fall in place; snap seam or mechanical seam, pan width, seam height, spanning capabilities, stiffening ribs, striations and in-place coverage. Do not get bogged down with multiple manufacturers. Set your standards and design for your project. List a couple that are comparable.
Top quality roof systems should have top quality high-performance accessories called out as well.
Rib and ridge closures: Provide prefabricated, factory pre-notched closures to match the rib profile with close-fitting components in the same color and finish as the roofing panel.
Sealants: Elastomeric, clear tri-polymer, as recommended by the manufacturer, and high-performance butyl tape with spacer cubes to prevent bottoming out of the sealant during compression.
Fasteners: By or as recommended by the panel manufacturer.
Snow guards: Prefabricated, non-corrosive units designed for compatibility with metal roofing system layout as per the manufacturer’s design.
Underlayments: Synthetic underlayments have made great advancements in the past few years with high-temperature self-adhesive for use around the building perimeter and flashings, along with the woven synthetic replacing the 15-pound or 30-pound felt with red rosin paper slip sheet.
Ventilation: The use of above-sheathing ventilation (ASV) is making its way into the roof assembly with vapor permeable underlayment in conjunction with above sheathing spacers.
Installation should be in accordance with the shop drawings, minimizing field cutting, cleaning exposed sheet metal work at the completion of installation, leaving the work clean and unmarked, and free from dents, creases, waves, scratch marks or other damage to the finish. You can engage an independent third-party, factory-authorized service representative to inspect completed metal roof panel installation, including accessories. Always remove and replace applications of metal roof panels where inspections indicate that they do not comply with the specified requirements.
David Weidl, CSI, CDT, LEED AP BD+C, is the architectural business development manager for ATAS International Inc., Allentown, Pa., and has been with ATAS for 20 years. For more information, visit www.atas.com.