The answer to this question varies with the load direction, the seam profile, the roof material and the clamp model. We have done hundreds of tensile load tests parallel to the panel seam and on various gauges and profiles, we have tabulated the results for your convenience. See Load Test Results for that information. In this load direction any loads that are introduced into the clamp will accumulate into the point of fixity. Panels must be adequately attached to resist these loads.
With very few exceptions, the attachment of a single S-5! clamp (even the “Mini”) to the seam will be stronger than a single point of attachment of the seam to the building structure. Hence the “weak link” is not the S-5 clamp, but the attachment clips that hold the metal panels to the building structure, or the beam strength of the roof panel seam, itself. Ultimate loads normal to the panel seam (both positive and negative) are more a function of the panel’s beam strength, and the failure strength of the panel’s attachment clips than of the holding strength of the S-5! clamp on the panel seam. These values will also change with various attachment spacing.
ASTM standard E-1514-93 for structural standing seam metal roofing states that panels must withstand a minimum 200-pound point load in positive (downward) pressure at the panel’s weakest point (the flat of the panel). The Army Corps of Engineers Technical Instructions for metal roof design spec (TI 809-29) says that the same value should be 300 pounds.
Almost any structural metal panel system will meet the above specifications easily. Of course the seam area is also much stronger than the panel flat. Hence, as a general rule, 300-pound positive point loads on the panel seam (above an S-5! clamp) should do the panel no harm. HVAC units have been mounted in this fashion on numerous projects, utilizing four, six or eight clamps for a single unit of considerable weight, and dividing the weight of the unit evenly over those point loads. Of course, the building structure must also be designed for these loads.
S-5! clamps have been laboratory tested on various seam types, profiles and materials for ultimate failure loads parallel to panel seam (“drag” type loads). The ultimate load-to-failure results vary with individual panel profiles and gauges. When used on some “applied cap” architectural type seam styles, for example, S-5! may yield low load-to-failure results and may therefore be unsuitable.
Also, keep in mind that the setscrews, which make a small dimple in the panel seam, optimizing holding strength, are normally tensioned to 115 inch-pounds for test purposes. This is because the tools normal to the trade are rated at this tightening torque. But there are some exceptions to this rule. On some profiles and gauges in steel, screw tension of 115 inch-pounds will not adequately dimple the panel seam. In such cases, load-to-failure values would be rather low, but for increasing the screw tension. For this reason, the tests are run with higher screw tensions on some profiles. On the other hand, there are very few seams on which the clamp screw engages only two thicknesses of sheet metal. When such material is thin-gauge aluminum or titanium-zinc, the setscrew may pierce through at normal tensions of 115 inch-pounds. For that reason, such seams are tested at lower set screw tensions. Regardless of application, appropriate factors of safety should be always employed and screw tension verified when relying on these test results.