Metal roofing fits into two main categories: Structural and Architectural.
Structural metal panels are typically used on low pitch applications. The metal panels are usually installed directly over purlins, effectively becoming both the roof deck and the actual roof. Wide rolls of insulation (typically 2-3 inches thick) are typically draped over the purlins prior to the installation of the metal panels.
(While the life expectancy of the metal itself is quite long, metal is a poor waterproofing material. The normal expansion and contraction of metal creates predictable problems in this application, and it is quite common for metal roof owners to report that their metal roof has leaked since the day it was installed. Our metal retro-fit solution provides a long-term solution to your chronic metal roof leaks.)
Architectural metal roofing is typically installed only on steeper pitched roofs (3:12 or greater in most cases) to ensure proper water runoff. These roofs are water shedding, not water proof. They are installed over a wood or metal deck, or in some applications, directly over an existing roof.