26 September 2006
When paint coatings are used for exterior applications they must be 0.0254 mm (1 mil)
dry film thickness consisting of .00635 mm (0.25 mil) prime coat and 0.019 mm (0.75
mil) finish coat minimum applied by the continuous coil coating method. Paint resin,
with noted exceptions, must be 70% polyvinylidene fluoride (PVDF) containing 100%
inorganic pigments. Exceptions include interior applications, soffit applications, and
surfaces painted white. In these cases, the resin type may be siliconized polyester
(SMP) with organic or blended pigments. Many other resin types (including PVF) are
available but should only be considered for unusual environments or uses.
Paint coatings must be applied over metallic coatings for carbon steel. Organic
coatings must be directly applied to aluminum material.
When aluminum substrates are used the minimum required thickness is .81 mm (.032
in.). When coated steel substrates are used, the minimum required thickness is 24-
gauge. (The nominal thickness according to industry standards (not including metallic
coating) for 24-gauge steel is 0.6071 mm (0.0239 in.), and the minimum thickness is
0.5309 mm (0.0209 in.).) Heavier gauges may be necessary to meet wind uplift criteria.
The specification mandate of heavier section thickness such as 1 mm (0.040 in.) for
aluminum and 0.76 mm (22 gauge) for steel may improve the aesthetic with respect to
In any event, the minimum panel material thickness must be consistent with the material
thickness as it was tested for structural capacity in ASTM E1592-01 Standard Test
Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform
Static Air Pressure Difference.
Use a flat pan, vertical leg standing seam profile with minimum finished seam height of
38.1 mm (1.5 in.) with a double fold (180 degree) seam or a 50.8 mm (2 in.) minimum
seam height with single fold (90 degree) seam and capable of meeting wind resistance
requirements. In general, the greater the seam height the greater the beam strength
and wind resistance of the panel and the less potential to leak in ice damming
Ultimately the panel type decision is aesthetic, economic, and functional. It may also be
dictated by wind uplift performance. The effects of oil canning are minimized by fluting,
striation, pencil rib or other formations to disrupt the panel flat. However, formations
such as these that result in an offset dimension greater than 3 mm (0.125 in.) in height
are not allowed due to excessive voids created at panel termination points. When flat
pan configurations are used (no disruptions in the flat), tension level coil must be
specified to ensure flatness. Panel width must be between 300 and 450 mm (12 and 18
in.) with a 400 mm (16 in.) panel type widely available. Panels must be furnished in
lengths of 18 m (60 ft.) or longer, when possible, to minimize or eliminate end-to-end
joints (panel laps). Panels must be factory fabricated wherever possible. Site forming
can be considered only with special approval.