Metal Roofing

Curtis Liscum, RRC

Metal roofing has been described as the oldest "single-ply" roofing system on the market today, dating back to the 1600s in the United States. In fact, Paul Revere took up roofing after the revolution and handcrafted the metal roof dome on the Massachusetts State House in 1798, which is still in use today.

Due to its limited usage, (only 3-4% of the reroofing market), describing or even discussing metal roof systems can be confusing. Available in the market today are architectural or structural panels, Batten seams, Bermuda panels, corrugated sheers, shingled panels and standing seam systems. To assist in clarifying this confusion, I will discuss the metal roof system in two general classifications: those that shed water and those that are moisture barriers.

The water shedding systems are similar in concept to shingles, tile and slate. They are generally installed as an architectural system on slopes greater than 3:12 over base felts and a structural deck system. The seams on these types of systems do not have to be perfectly watertight due to the roof's slope and drainage characteristics. The panels are generally shorter in length with little necessity for significant panel thermal movement. Water shedding systems are usually seen as the aesthetically pleasing mansard or facades on facilities.

In comparison, the moisture barrier systems are similar in concept to the standard built-up, single-ply or modified bitumen roof system in use today. They can be installed 1/4":12. These structural systems are installed with insulation and vapor barriers directly over structural framing purlins. The seams must be watertight, and due to the panel lengths and general roof area size, panel, fastening clips, splices, end details and side details, must accommodate the thermal expansion and contraction of the metal system.

As with any roof selection process, the roof system selected must be based on the system that is best suited for the facility. Features that make structural standing seam systems attractive include:

• Weathertightness
• Durability
• Low maintenance
• Life-cycle costing

It is not my intent to conclude that metal roof systems are appropriate or even desirable for every roof area. However, given the right set of conditions, metal roof systems could be the long-term roof replacement system you have been looking for.