Mounting HVAC on Metal Rooftop

Many HVAC units are mounted on pre-formed roof curbs and bottom-ducted to the building interior. Although S-5! has no application for these circumstances, in some cases a condensing or similar unit needs to be roof mounted but does not need to duct through the roof. S-5! is the solution. On other occasions, units are placed near an adjacent wall, and then ducted through the wall rather than the roof. Such practice is prudent, as ducting through the wall is less expensive and less problematic than ducting through the roof. S-5! is the solution here, too.

The usual method is to mount the unit on wood blocking to raise it above the plane of the panel ribs, and give it a surface to bear upon. Placing the unit on lumber which bears on a sloped roof causes the equipment to sit out-of-level and operate less efficiently. It may also migrate if not anchored. If anchored, holes are punched in the roof. Additionally, there is little room for drainage beneath such a unit, and debris collects.

Debris holds moisture and can contribute to premature corrosion. Lumber is porous and will retain moisture. Treated lumber contains chemicals which accelerate corrosion. This is an example of what happens to the Galvalume® steel panels under such circumstances. The warranty on this long-life coating has now been voided due to this condition and the panels are badly corroded.

The S-5! solution: An equipment stand is built from a steel angle. The frame is mounted to the roof using S-5-U clamps. Now, the unit sits perfectly level and operates efficiently. Nothing obstructs drainage or collects debris. These units weigh 1,300 pounds each. That load is spread between eight bearing points (clamp locations). The result is 162 pounds point load at each location easily endured by the panel rib and seam.

S-5! clamps mount to the seam with no holes in the panels. The clamps provide holding strength measured in tons. The equipment stand is bolted to the clamp with stainless steel bolts (included with each clamp). The equipment cannot migrate from its intended location. All warranties are preserved.

Ductwork often has to run some distance over a standing seam roof. It may run from a unit through an adjacent wall, or serve as an intake or exhaust extension. Once again, the wood blocking sometimes comes into play. Alternatively, a light-gauge steel frame is built (as pictured). This is more appropriate than wood blocking. The problem is how to attach the support frame.

Here, it is screwed through the roof panel and into the underlying structural member. The steel angle is carefully caulked to the roof, but this exposed sealant doesn t last long before it deteriorates and begins to leak (which, of course, is an exclusion from the warranty). The panels are now pinned at this location, thus the thermal movement integrity of the system has been jeopardized, also violating the warranty.

The S-5! solution: Once again, the ductwork is supported by light gauge angle iron framing. This time, the angle frame is mounted to the roof with S-5!

No holes. No sealants. No warranty violatons. No problems!