Q & A: Best Practices for Using S-5! Clamps

What are the best design and installation practices when using S-5! clamps to structurally attach PV systems to standing seam metal roofs?

Standing seam metal roofing (SSMR) is the most convenient of any roof type for mounting PV modules, either crystalline or thin-film. The seams of SSMR are beam-like elements that not only add stiffness and flexural strength to the roof panels, but also provide expedient attachment points for a PV system. Joining PV modules to this roof type can be done with or without continuous mounting rails using aluminum S-5! seam clamps. These patented clamps anchor to the roof seam by pinching it within the clamp body with round point setscrews that are in no way invasive to the roof. The clamp body is machined with threaded holes to facilitate anchorage of PV modules or racking components to the clamp.

The SSMR industry has used this attachment technology for many years, and most SSMR manufacturers endorse and recommend this method when making attachments of various ancillaries to their roof systems. It is of prime concern to all parties - building owner, roof manufacturer, PV integrator and S-5! Attachment Solutions - that the integrity of the roof system is maintained and attendant warranties, if any are in place, are not jeopardized. The result is a PV-to-SSMR marriage that provides maintenance freedom for the expected service lives of both the PV system and the roof. When properly executed, these methods are not only dependable and expedient, but also cost effective - saving up to $1.00 per watt when compared to other roof types and mounting systems.

To achieve the perfect marriage between a PV system and the SSMR using S-5! clamps, follow the best practices described below.

Compatibility. Metallurgical compatibility is always important on a rooftop where materials will be in electrolytic contact. SSMR is most often steel, occasionally aluminum and very rarely copper, stainless or some other metal. Steel and aluminum may be prepainted (coil coated) or bare. The latter is something of a misnomer. Steel will always have a protective coating of pure zinc (galvanized) or an aluminum/ zinc alloy (Galvalume or Zincalume) for corrosion protection.

Aluminum S-5! clamps are compatible with all these metals except copper. When roofing is copper, brass S-5! clamps should be used. Somewhere between the brass clamp and the aluminum PV frame an electrolytic switch must be made. This can be done with a passive metal like stainless steel or with rubber isolators or both.

Some installers might want to use the galvanic scale to identify dissimilar metals, but the graphical galvanic scale is not always a good way to determine whether one metal is compatible with another. The reason is that when metals oxidize, the oxide layer created is a new material that may or may not exhibit the electrochemical characteristics of the parent metal. Therefore, the scale does not always tell the whole truth.

Another compatibility issue has to do with the shape or profile of the SSMR seam itself and the S-5! clamp model selected. Many different seam geometries exist, along with a number of corresponding S-5! clamp profiles. Examining and verifying the dimensions of the seam in question prior to consulting the S-5! Web site (S-5. com) can determine the proper match for a mating clamp. The site shows various clamp profiles, nomenclatures and critical dimensions that should enable selection of the appropriate clamp to fit the SSMR.

Clamp holding strength. The holding strength of the S-5! clamp is tested in two different load directions: parallel to the seam direction and perpendicular, or normal. These replicate drag loads such as sliding snow and uplift loads induced by wind effects. Ultimate and allowable loads (factor of safety = 2) are published on the S-5! Web site. Holding strengths are panel specific, varying with the seam material, gauge and profile of the SSMR. In order to determine the appropriate clamp and allowable load, these variables of the roof panel system must be identified. This is most easily done by matching the manufacturer name and the panel profile name to the listings on the Web site. When reviewing this data, keep in mind that most manufacturers make more than one profile.

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