The single most common question we field after a free-preview run is "do I owe solar on this one?" The 2025 Energy Code makes the answer cleaner than the 2022 cycle, but the scope rules still cross several sections of Part 6 and the wrong read can put a 1.8 kWdc array on a project that didn't owe one. Here is what the code actually says, and how we apply it on every project we run.

What the rule actually says

§150.1(c)14 — the PV mandate — applies to newly constructed low-rise residential buildings. The triggering event is "newly constructed," not "any project that touches energy." §150.2(a) governs additions to existing residences and §150.2(b) governs alterations; neither of those sections invokes §150.1(c)14. That is the entire load-bearing distinction.

The 2025 ADU FAQ then clarifies the in-between case: a detached ADU is its own newly-constructed dwelling unit and is subject to §150.1(c)14, while an attached ADU is treated as an addition to the primary residence under §150.2(a) and is exempt from the PV mandate.

How that lands in practice

The scope matrix we apply when sizing PV:

  • Newly constructed single-family — PV required, sized per Table 150.1-C.
  • Newly constructed detached ADU — PV required, sized per Table 150.1-C with NDU contribution.
  • Newly constructed attached ADU — treated as an addition; not required.
  • Addition or addition+alteration to an existing residence — not required.
  • Alteration only — not required.

There is a corner case worth naming: a project filed as "Add-Alone" (an addition that the designer models as a standalone structure for separate permitting) is still an addition for §150.2(a) purposes if it is non-ADU or an attached ADU. We handle those as additions so the compliance result reflects the §150.2(a) framing the code intends. A detached-ADU Add-Alone is the only case that stays on the new-construction track.

What designers should do differently

Three places to double-check before assuming an array is required:

1. Look at the scope of work on Sheet G-001 first, before sizing solar. A "remodel + 320 sf addition" is an addition; modeling it as new construction triggers solar that the AHJ won't ask for at plan check. 2. For ADUs, confirm attached vs detached on the site plan. Anything sharing a wall, shared roof framing, or a common interior door with the primary residence is attached. A breezeway-only connection that doesn't share conditioned envelope is detached. 3. Don't conflate "scope-exempt" with the §150.1(c)14 Exception 2 small-project carve-out. Exception 2 is for small new construction whose prescribed array calculates under 1.8 kWdc — that's still new construction, just with a math result that lands at zero. Additions and alterations are exempt by scope, not by exception.

Your design options will show a "Solar PV is not required — addition / alteration scope" line when the scope rule applies, instead of the §150.1(c)14 exception language. If you see the exception wording on what is genuinely an addition or alteration, flag it and we'll correct it.

The reference table you'll actually use

Table 150.1-C is the prescribed-PV sizing table: CFA × CFAmult / 1000 + NDU × DUmult. NDU is 2 for any project with an ADU on the parcel, 1 otherwise. The CFAmult and DUmult are climate-zone specific and come straight from the CEC's published climate-zone baselines — there's no compliance benefit to deviating from those numbers.