Fictitious Plans Design - Part 1

Few solar installation companies consistently access the attic. Whose job is it to lie about the structural details?

Sometimes I get asked to redraw plans by others. While I'm always curious what my competitors are doing, I am sometimes gobsmacked by how often plans designers and engineers simply lie.

Don't get me wrong - for most residential projects, we can infer plenty from rafter tails and year of construction. Heck, many jurisdictions don't even require rafter info for flush-mounted installs. But I have run across various projects where the framing details do matter, and the installer is surprised that I need more information.

After all, tons of design firms and engineering firms will simply invent the site details - why am I making things harder by requesting a re-assessment?

Spoiler alert: ballasted PV projects are heavy because you are literally installing concrete blocks

The project

I was asked to redraw a residential ballast-mounted system in San Francisco for a large installer. It had been languishing in plancheck limbo for almost a year, because of what seemed like an insurmountable amount of corrections.

The 17-module installation would weigh almost a full ton. San Francisco is in a seismic zone, and this property is near the shoreline - which means an Exposure D wind category. The AHJ had good reason to be picky with these calculations.

Fiction 1: Inventing the roof framing details

No matter how professional a plan set appears to be, invented info is amazingly common

The original designer claimed this structure had 2x10's @ 24" OC. But, as my engineering contact remarked, "2x10 rafters are very rare in San Francisco for homes built back in the 40's."

If the Los Angeles-based engineer I work with was able to tell that the information was fabricated, then the San Francisco planchecker was definitely able to tell the original details were completely made-up.

When plans have been so obviously caught in a lie, I like to include photos in the next submittal to try to salvage some trust with the planchecker. So we asked the installer to go back to verify the rafter dimensions, and sure enough, they were a true 3x6 @ 32". After some back-and-forth with the engineer to re-arrange the concrete block locations, we managed to find a solution where no retrofit was required.

While it's always fun to spot some old knob-and-tube wiring in the attic, these are not 2x10's

Fiction 2: Embellishing the roof size

The U-Builder is a free tool provided by Unirac to perform site-specific engineering calculations. The renewable energy industry is rife with amazing free tools - products are simply more attractive when technical services are included. However, these tools are not foolproof, and misuse of them is pretty common.

Case in point: the original designer drew the roof bigger than it actually was in the Unirac configurator. Why does this matter?

These two images are shown at roughly the same scale. The first image is the original U-Builder report: notice that the the black 'setback' line is at the edge of the roof, and the white roof outline has been overdrawn by about 3'. The second image is the redrawn U-Builder report.

Ballast systems need a certain amount of setback from the roof perimeter (typically 3' for residential) because of increased wind uplift at the edges of a structure. The original designer used a false outline of the roof to manipulate the calculations, and make it look as though Unirac 'approved' the installation of modules within inches of the roof's edge.

What's the worst that could happen?

Ballast systems are finicky because, unlike most PV systems, they are not physically attached to the roof using screws. In seismic areas like California, small decking attachments are used to stop the array from shifting during an earthquake - but commonly-overlooked parameters like edge distance and parapet height are fundamental in making sure the array will not be lifted off the roof in the case of a severe wind event.

Plus, ballast systems weigh a ton - the roof could actually cave in. Whether or not the city is thorough with their plancheck, I would encourage all installers to find out the actual framing information - if not for their own liability's sake, then at least out of concern for their clients' wellbeing.

Let's not

Final thoughts

So, I am not an engineer - and most project managers and contractors aren't engineers either. But it is still useful for all industry professionals to know the basics about ASCE wind zones and roof zones. A common theme that I see is this: needing to find out the actual site details often delays projects by months.

As nationwide installers gain more traction, a volume-driven approach to solar installation has become the norm. Where does the liability lie between the contractor actually installing the solar modules, and the larger corporation providing the plans? Permits are often issued to the contractor's license of the larger corporation - who in all likelihood would deftly navigate any potential lawsuit. And in the absence of a rigorous AHJ, the homeowner is the one who will pay the price.