§150.1(c)14 in plain English
Title 24 Part 6 §150.1(c)14 requires every newly constructed low-rise residential building to install an on-site solar photovoltaic (PV) system. The required size is calculated from the building's conditioned floor area and dwelling-unit count using per-climate-zone factors. The intent is for the average new home to produce roughly as much electricity over the year as it consumes — effectively net-zero electricity on an annual basis.
§150.1(c)14 was first added in the 2019 code update and remains substantially the same in the 2025 cycle. What changed in 2025 is the surrounding scope clarification: the CEC's ADU FAQ confirmed that detached ADUs are treated as newly constructed structures and trigger §150.1(c)14, while attached ADUs and non-ADU additions are treated as additions to existing residences (under §150.2(a)) and do not.
When PV is required — and when it isn't
| Project scope | PV required? | Why |
|---|---|---|
| Newly Constructed single-family home | Yes | §150.1(c)14 directly applies. |
| Newly Constructed single-family with an ADU on the same lot, permitted together | Yes (sized for both) | §150.1(c)14 applies; NDU=2 in the formula. |
| Detached ADU as standalone Add-Alone (existing residence on lot) | Yes | 2025 ADU FAQ classifies detached ADUs as new construction. |
| Attached ADU as Add-Alone | No | Treated as an addition to the existing residence per §150.2(a). |
| Non-ADU addition as Add-Alone | No | Treated as an addition per §150.2(a). |
| Addition and/or Alteration to existing residence | No | §150.2(a) / §150.2(b) do not invoke §150.1(c)14. |
| Alteration Only (no new floor area) | No | §150.2(b) addresses alterations separately from §150.1(c)14. |
In our compliance engine, the function _pv_required_by_scope in the
design-options builder makes this determination from the project scope and ADU type.
When PV is scope-exempt, the design-card highlight reads "Not required (addition /
alteration scope)" rather than citing an exception number — the project simply isn't
under §150.1(c)14 at all.
The sizing formula
The per-CZ factors are published in the Title 24 compliance ruleset's
T24RClimateZoneCodeBaselines.csv (the "SingleFam" rows). The formula
itself is from Rules_Default_PV.rule in the same rule library:
PV_kW = CFA × CFAmult / 1000 + NDU × DUmult
Where:
- CFA = conditioned floor area in square feet. For Newly Constructed projects, this is the whole-home CFA. For NC main + ADU together, this is the combined CFA.
- NDU = number of new dwelling units in this compliance run. 1 for an NC main alone. 2 for NC main + ADU permitted together. 1 for a detached ADU as standalone Add-Alone (only the ADU is new in this run; the existing main residence isn't part of the §150.1(c)14 calculation).
- CFAmult / DUmult = per-climate-zone factors from the Title 24 baseline data.
Per-climate-zone factors
These come directly from the Title 24 T24RClimateZoneCodeBaselines.csv
SingleFam rows and are the same factors our compliance engine uses to size the PV
output:
| Climate zone | CFAmult | DUmult | Notes |
|---|---|---|---|
| CZ1 | 0.793 | 1.27 | North Coast (Eureka). |
| CZ2 | 0.621 | 1.22 | Wine Country (Santa Rosa, Napa). |
| CZ3 | 0.628 | 1.12 | Bay Area coast (SF, Oakland). |
| CZ4 | 0.586 | 1.21 | South Bay / Salinas Valley. |
| CZ5 | 0.585 | 1.06 | Central Coast (Santa Barbara, SLO). |
| CZ6 | 0.594 | 1.23 | LA coastal basin (Long Beach). |
| CZ7 | 0.572 | 1.15 | San Diego coast. |
| CZ8 | 0.586 | 1.37 | Coastal Orange County. |
| CZ9 | 0.613 | 1.36 | Foothill LA County (Pasadena). |
| CZ10 | 0.627 | 1.41 | Inland Empire west (Riverside). |
| CZ11 | 0.836 | 1.44 | North Sacramento Valley (Chico). |
| CZ12 | 0.613 | 1.40 | Sacramento, Stockton, Modesto. |
| CZ13 | 0.894 | 1.51 | South Central Valley (Fresno, Bakersfield). |
| CZ14 | 0.741 | 1.26 | High desert (Palmdale, Victorville). |
| CZ15 | 1.560 | 1.47 | Low desert (El Centro, Indio) — highest CFAmult. |
| CZ16 | 0.590 | 1.22 | Sierra / mountain (Truckee, Mammoth). |
Source: Title 24 T24RClimateZoneCodeBaselines.csv SingleFam rows, 2025.
A worked example: a 2,500 sf newly constructed single-family home in CZ13 (Fresno), NDU=1.
PV_kW = 2500 × 0.894 / 1000 + 1 × 1.51
= 2.235 + 1.51
= 3.745 kWdc
The same home in CZ7 (San Diego) lands at 2500 × 0.572 / 1000 + 1 × 1.15 =
2.58 kWdc — about 31% smaller, because CZ7 has both lower CFAmult (less solar
production per square foot needed) and lower DUmult.
Our compliance engine applies a +10% safety pad to the raw number above before writing it to the report. The pad isn't part of the regulatory threshold — it exists so that the proposed PV credit comfortably matches the Standard Design PV credit at compliance time. Without the pad, borderline cells (proposed efficiency margin positive but PV credit just barely matching) fail with a -0.05 to -0.20 LSC margin. A 10% pad buys ~0.3 LSC headroom which clears the borderline. So the 3.745 kW Fresno example above ships as 4.12 kWdc on the report.
§150.1(c)14 Exception 2 — small-project waiver
§150.1(c)14 Exception 2 waives the PV requirement when the prescribed system size
falls below 1.8 kWdc. This is most common on small detached ADUs in
low-CFAmult climate zones. A 500 sf detached ADU in CZ7 (San Diego coast) calculates
to 500 × 0.572 / 1000 + 1 × 1.15 = 1.44 kWdc — below the 1.8 threshold,
so PV is waived under Exception 2.
What the report actually shows in the Exception 2 case: PV size = 0 kW. The exception itself isn't stamped on the certificate as a named flag — the compliance engine infers it from the prescribed PV calculation falling under the threshold. Every reference file we've seen handles Exception 2 this way. Our compliance engine mirrors that convention; the design dashboard surfaces "PV size: 0 kW (Exception 2 — small project)" for visibility, but the underlying compliance input stays clean.
The threshold trigger isn't symmetric with the safety pad above. The 1.8 kWdc check uses the raw formula output (no +10% pad) because the safety pad is a compliance-margin convenience, not part of the regulatory test. A project at 1.7 kW raw / 1.87 kW padded is exempt; a project at 1.8 kW raw / 1.98 kW padded is not.
NDU mechanics — main + ADU vs ADU alone
NDU (Number of new Dwelling Units in this compliance run) deserves its own sub-section because it trips up architects regularly. The rule:
- NC main alone: NDU = 1. PV sized for the main residence's CFA.
- NC main + new detached ADU permitted together: NDU = 2. CFA in the formula is the combined CFA. PV sized for both.
- Detached ADU as standalone Add-Alone (existing main residence already permitted): NDU = 1. CFA in the formula is the ADU's CFA only. The existing main residence is not part of this run's §150.1(c)14 calculation.
- Add+Alt to existing residence: §150.1(c)14 doesn't apply at all regardless of NDU.
In practice: a 1,000 sf detached ADU in CZ12 added to a lot with an existing 2,500 sf
main residence calculates 1000 × 0.613 / 1000 + 1 × 1.40 = 2.01 kWdc —
just above the Exception 2 threshold, so PV is required, but only sized for the ADU.
The existing main residence's CFA does not enter the calculation.
What the Title 24 report shows — and doesn't
The report shows the required PV system size in kWdc. That's it. The report does not specify:
- The specific panel manufacturer or wattage (e.g. "REC Alpha Pure 410W" or "Q.PEAK DUO BLK ML-G10+ 395W").
- The inverter selection (microinverters vs string inverter vs power optimizers).
- The panel layout on the roof.
- The interconnection point (panel sub-feed vs main panel busbar).
- Battery storage (an optional add-on that doesn't satisfy §150.1(c)14 by itself).
Those decisions belong to the solar contractor and get captured on a separate CF2R Solar Photovoltaic certificate at install time. The architect and energy consultant set the required size; the solar contractor delivers it.
One consequence: a CF1R can be registered and signed before the solar contractor has even been selected. The required kW is fixed by the design and the climate zone — the contractor just has to hit that number. This is why the responsible designer can sign the report without coordinating with the solar contractor first.
Storage, curtailment, and post-NEM3 economics
§150.1(c)14 is satisfied by the PV system alone. Battery storage is permitted (and typical with modern installs given NEM3 export economics) but not required for §150.1(c)14 compliance. A project that installs PV without storage still passes; a project that wants to add a battery for self-consumption can do so independently.
Two related compliance pathways worth knowing:
- Battery + reduced-PV path. Title 24 supports a compliance path where a battery substitutes for some of the prescribed PV. This is the ReducedPVReq flag in the compliance schema. We don't take this path on current projects because the equipment specification gets complex and the customer savings are usually modest, but it's available.
- Community Shared Solar exemption. §150.1(c)14 Exception 1 allows participation in a CEC-approved Community Shared Solar program to substitute for on-site PV. Vanishingly rare in single-family residential at the moment.
Practical takeaways for designers and contractors
- For NC projects, expect 2.5–6 kWdc of required PV depending on CFA, NDU, and climate zone.
- For small detached ADUs (under ~800 sf in CZs with CFAmult ≤ 0.7), Exception 2 may waive PV entirely. Worth checking before bidding solar into the budget.
- For Add+Alt and attached-ADU Add-Alone projects, PV is exempt by scope — no solar required on the permit.
- The report's kW number is fixed; the solar contractor's job is to install enough panels and inverter capacity to hit it. The CF2R Solar PV certificate documents the actual installation.
- The safety pad on the proposed PV credit (+10%) exists to keep compliance margin healthy. It is not a regulatory requirement; if a contractor proposes 5% less than the report says, the project still satisfies §150.1(c)14 — but it may show a thinner LSC margin on the final compliance run.