What you're looking at

A schematic plan view of a south-facing roof plane (eave at the bottom, ridge at the top) with a 24-panel array laid out in 3 rows of 8. The dashed lines show the required clearances: a setback from the ridge and a fire- access path that lets firefighters reach the ridge from the gable end.

How the size is calculated

The prescriptive formula is in §150.1(c)14 and the table is in the Title 24 climate-zone baseline file:

`` kWdc = CFA * A/1000 + NDU * B ``

Where:

- CFA is the conditioned floor area in square feet - NDU is the number of new dwelling units in this compliance run (1 for main only, 2 for main + ADU) - A and B are the per-zone CFA and DU multipliers

For a 2,400 sf newly-constructed home in CZ12 (Sacramento), the multipliers are 0.613 and 1.40:

`` kWdc = 2400 * 0.613/1000 + 1 * 1.40 = 1.47 + 1.40 = 2.87 kWdc ``

That's about 7 modern 400W panels.

When the array can be smaller

- §150.1(c)14 Exception 2. Projects where the prescribed PV is below 1.8 kWdc are exempt (typical for small ADUs in low-PV-factor zones). - Additions and alterations. §150.2(a)/(b) projects do NOT invoke §150.1(c)14 except for newly-constructed detached ADUs.

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