CalFire Setbacks

What’s the Problem?

The problem is threefold:

  1. Three-foot corridors use up a lot of roof surface.
  2. Many roofs are complicated — and the guideline seems to suggest more and more access paths.
  3. Common-sense can slip through the cracks. If the whole northern roof is unencumbered, are setbacks really needed on the southern side, where solar would go?

Let’s look at each of these issues.

Three-foot corridors use-up a lot of roof surface.

Setbacks can really change the economics of a residential solar installation. To understand how, grab a sheet of regular, 8.5” x 11” paper, and hold it sideways. That’s a roof plane — perhaps the south side of a garage, with perfect sun. (In the graphic below, I’ve tilted this sheet of paper back a bit, to suggest a roof.)

Now cut off 3 inches on the left, right, and top. The surface area was 8.5 x 11 = 93.5 square units. Now the area available for panels is only 27.5 square units – a loss of 70% of the potential space!

Many roofs are complicated — and the guideline seems to propose more and more access paths.

The issue here is that a surprising number of roofs have extra planes. And per the reg, if a rectangular roof plane needs access paths on either side, then two rectangular roof paths seem to call for twice as many access paths.

Here’s a simple example — a roof in Sonoma, California

The garage’s roof (left) and the house’s roof are not the same plane, and thus the reg can easily be interpreted to require access paths on the left and right of each of these roofs, as well as across the ridge line.

Here’s another roof; this one in Sebastopol:

With subtle changes in slope, is this lower roof one large roof plane, or three or more?

Common-sense can slip through the cracks.

If the whole northern roof is unencumbered, why are setbacks needed on the southern side — the side where panels would be installed?

For the home above, it’s clear that there’s one perfect roof plane for solar, as there’s only one large piece of south-facing roof. Are side and ridge setbacks really needed on that piece, or can the easy access across the rest of the roof be considered when approving solar?

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