CEMP-ET
TI 809-53
01 May 1999
CHAPTER 9
METAL ROOFING
REFERENCES
CEGS 07412 Nonstructural Metal Roofing
CEGS 07416 Structural Standing Seam Metal Roof (SSSMR) System
ASTM E1514 Structural Standing Seam Steel Roof Panel Systems
9-1. OVERVIEW OF METAL ROOFING. Included in this section are factory-formed metal panels which
may be used in low-slope roof applications (hydrostatic), and factory or field-formed panels and other
shapes that are used in steep roofs (hydrokinetic) (figure 9-1). Either type will have varying structural
characteristics (e.g., ability to resist applied loads between supports or anchorages).
a. Terminology.
(1) Low-Slope. Only factory-formed panels should be used for low-slope roofs. They require
standing seams elevated more than 37 mm (1-1/2 in.) above the flat of the panel. Factory-applied
sealants (figure 9-2) at sidelaps, and field-applied sealants at endlaps are required to enhance
waterproofness. Seams must be squeezed tight with a mechanical device once the system is
assembled. Minimum slope is 4% (1/2 in/ft.).
(2) Structural Panels. Structural Panels are long metal panels with sufficient beam strength to
carry design loads while spanning between clips supported by framing members often spanning about 1.5
m (5 ft.). Large thermal movements accumulate in long metal panels. Two-part sliding clips are needed
to allow such panels to float (i.e., to expand and contract freely as their temperature changes). If such
panels are firmly attached to the frame of the structure at more than one place along their length, this
freedom is lost. Waterproofing low-slope metal panels at their free ends, in valleys and at penetrations is
not easy. Thermal movement in the cross-slope direction is accommodated within each seam and does
not accumulate from panel to panel.
(a) Structural panels are commonly used within the pre-engineered metal building industry
where they are supported by cold-formed purlins or bar joists. They are also used widely in mansard and
equipment screen type applications, which are constructed with open framing members. They are used
extensively in reroofing applications to avoid having to add a continuous deck needed by nonstructural
panels. When they are used over structural decks their structural characteristics may not be fully utilized.
Not all structural panels are suitable for low-slope (4% [1/2 in./ft.]) applications but most low-slope panels
are structural panels. [A typical design load may be 1.44 kPa (30 psf) positive or negative while spanning
not less than 914 mm (3 ft) in a continuous (3 or more) span condition. Maximum span length for
corners, edges and edge zones is 750 mm (30 inches).]
(b) Clips for structural panels must be screwed or bolted into structural framing. Attachment
of structural panel clips to metal decks, or other decks with questionable pull-out capacity, should not be
permitted.
(3) Nonstructural Panels. Nonstructural panels are always supported on an underlying
substrate. Batt insulation does not provide such support. Nonstructural panels are installed over wood or
metal decks or over noncompressible insulation boards. The clips that attach them are typically screwed
or nailed into a nailable deck and screwed into a non-nailable deck. Clip spacing is commonly 300 mm
(12 in.) to 500 mm (20 in.) for standing and batten seam profiles. Very few nonstructural panels are
suited for use on low-slope roofs. Most are for steep-sloped architectural applications with watershedding
underlayment. Nonstructural panels may use standing, batten, or flat seams. The shadow line provided
by vertical ribs (or battens) and the availability of durable, factory painted panels in many colors make
9-1
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