26 September 2006
CHAPTER 4 METAL ROOFING DESIGN REQUIREMENTS
Metal roofing can provide excellent performance, durability, and long service life. Metal
roofing can be used at virtually any slope. All projects are to be hydrostatic (water tight)
in design, not hydrokinetic (water shedding), including both low and steep slope
applications. They may be installed over open framing (known as structural systems),
or over structural decks (architectural systems). They may be used for new roofing,
reroofing, and are notably effective for recover of deteriorated metal roofs or in low-
slope to steep-roof conversions without tear-off.
There are many metal roof types. Types other than described herein may only be used
when approved by the appropriate authority. These include special site-formed
projects, curved applications of profiles other than described herein, crafted metals (soft
metals, e.g., copper, terne, and zinc), and all face-fastened panel types.
Use the MBMA Manual as the primary reference for design. This chapter limits the
applicability of certain techniques permitted by the MBMA Manual. Where contents of
the MBMA Manual are acceptable without modification, those sections are not
Metal Roof Advantages.
Metal is generally lightweight, highly wind resistant, and environmentally friendly as it is
both sustainable and more than 60% recycled. In most environments, coated steel will
render a service life of 40 years or more, and aluminum will render an even longer
service life. When properly designed and installed, metal roofing requires very little
maintenance. Coated steel and aluminum substrates can be factory painted with
coatings that are highly reflective and qualify as "cool" roofs. Uncoated metals have
very low emissivity and contribute to a heat island effect. Standing seam profiles
provide excellent attachment substrates for photovoltaic (PV) arrays. Specify non-
penetrating attachment points for PV mounting. Metal roofing is not combustible and
will not support flame. With paint coatings, metal can add color and definition to most
architecture. Metal is constructible year-round.
Metal Roof Disadvantages.
Standing seam systems are less forgiving of installation error and more difficult to
remedy than multiple-ply roof materials, hence highly qualified installers are essential.
Individual standing seam metal panels that are mechanically seamed are not easily
replaced. Replacement can be expensive, but it is rarely necessary. Rooftop
mechanical equipment must be procured from special sources to ensure compatibility
with both the roof installation systems and types of metals. Internal drainage systems
are more expensive to install correctly. Complex roof geometries involving multiple
planes, hips, valleys, and dormers may drive costs disproportionately upward.