Do you need to worry about roof penetrations made for solar collectors?

One of the  most penetrating questions of solar thermal is how to attach the solar collectors to the roof. It’s one I get asked quite often: Is it safe to make those holes in my roofing material?

There are  many ways to ensure a weather-tight seal, whether using a flush-roof mount or an adjustable mount that tilts the collectors at an angle.

HTP standard collector mount for tilt-up with triangle feet.

HTP standard flush mount

In most climates, direct attachments provide a sufficient seal against the elements. This is where the solar collector mounts are bolted directly to the roof. The collectors can either be flush with the roof or standing at a tilt. The result  is eight roof penetrations for two flat-plate collectors. HTP’s standard mounts come in several styles: a triangle foot that allows the panel to be hinged for tilt-up at the chosen angle; and two flush mounts: one that lifts the collector ½ inch off the roof’s surface, the other lists the collector 3 inches.

When you want  to move a step beyond, say, the standard collector mounts, Unistrut is most commonly used for panel support. The advantage of Unistrut is that the collectors are attached to this steel beam, resulting in fewer roof penetrations. The least costly and most effective types of Unistrut are the 3″  thick or the double Unistrut. When bridging with this material, the roof mounting is attached comfortably at 7-foot distances, 8-foot distances for 4’x8’ or smaller panels. A contact at Hot Water Products Inc., based in Milwaukee, says that company utilizes 8-foot distances without sag on 4’x10’ panels.

I recommend the green 3″ deep Unistrut – NO galvanized. Galvanized steel cannot be bolted to the aluminum collector mounts. Spray a bit of paint over the Unistrut end cuts.

Example of stanchions installed on roof, with Unistrut attached to stanchions.

When a large system is installed on a flat membrane roof, curb-like stanchions can be installed. Unistrut is then attached to these stanchions, and the collectors mounted to the Unistrut.

Example of flashing used with a collector mount

There are some cases, however, where I advise the use of after-market attachments, or flashings, primarily for a shingled pitched roof. These include standoffs like those from Fastjack ( or the Qbase system from Quick Mount PV. The collectors can be mounted to this flashing directly, or Unistrut can span  across them and the collectors mounted to the Unistrut.

If you have a standing-seam steel roof, S-5 clips provide the best attachment without any penetrations. If you’re unsure what this blocky clip looks like, visit

Here’s my question to you readers: Should HTP have available for sale a flashing or moisture/rain barrier? What kind of issues are you seeing in the field regarding roof penetrations?

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