Structural solar hardware for flat roof assembly w/tapered insulation
I’m nailing down the design for a flat roof assembly in climate zone 3C, single family residential. Our architect has specified the following assembly:
Single-ply membrace roofing system (PVC) over
1/2″ recovery boards over
Tapered rigid insulation (min 1″ per T-24 report) over
1/2″ plywood sheathing w/ H clips over
framing w/batt insulation tight to sheathing (mineral wool)
5/8″ drywall
What specific solar hardware have you used that can be installed with a flat roof on top of rigid insulation?
I will probably end up asking the structural engineer on the project the same question. For now, we plan to use the Flat Roof Attachment by IronRidge, but I haven’t yet found documentation that it supports this specific assembly.
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Replies
All the commercial flat roof solar installs I've worked with had ballasted mounts. I don't see why these wouldn't work on a residential roof. I would not go for anything that puts screws through the membrane. Search for "ballasted flat roof solar rack system". They generally keep the panels at a lower slope which reduces winter production a bit but doesn't change the yearly production all that much.
Another option, if you have parapets, is to clear span with steel structure above the membrane and install racking on-top of this.
My preference is to have the structure incorporate some "hard points" that a seperate structure can be secured to to support the solar panels above the roof. I do the same thing if there are any antennas going on the roof. All the "hard points" are are rigid extensions up from the building structure through the roof that provide a secure attachment point for a support structure for the solar panels, and that support structure can be a purpose-built product, or can be site built from a support system like steel strut. This avoids the need for the solar installers to put in any new roof penetrations, all of which are potential failure/leak points for the roof. With the hard points pre-installed, the roofers can flash and seal all the structural attachment points before the solar installers show up on the site.
It's easy to put in hard points made of steel pipe if you use the usual roof "boots" used for things like vent pipes and electrical conduits. It's also possible to extend wood pieces up. Do whatever works best in your application.
I'm not a fan of ballasted mounts for two reasons: 1- they often aren't sufficiently ballasted (not all concrete blocks installed, hollow instead of solid blocks used, etc.), which leads to 2- stuff can blow off the roof during high winds and cause damage. Many commerical buildings will no longer permit the use of ballasted mounts because of problems with them getting blown off of roofs and damaging cars in the parking lots. It's safer to have secure structural mounts that won't move or lift.
Bill
This product looks similar in design to the pipe-format "hard points" Bill suggests. https://www.ironridge.com/component/qbase-low-slope-mount/
The installer drills through the insulation (2" hole or so). The hardware is fastened to the rafter or sheathing. Insulation is then added. Flashing is then added for the protruding cylinder.
One potential problem with this is the pipe boots I've seen add a fair amount of height. IronRidge recommends using "chemlink ecurb," which seems to add only 3" of height and is probably acceptable to us.