Title 24 in Ontario, Climate Zone 10
Ontario sits in California Title 24 Climate Zone 10, which sets the prescriptive baseline every Ontario residential project has to meet (or beat) under the energy code. The CEC assigns climate zones by ZIP code, every Ontario address resolves to CZ10 unless you're on an unusual edge ZIP (use the ZIP-code lookup tool to verify).
Prescriptive baseline for Ontario projects
These are the values your Title 24 report has to demonstrate compliance with. The prescriptive path matches them directly; the performance path can trade between them as long as the modeled energy use comes in at or under the reference design.
| Component | Value |
|---|---|
| Ceiling | R-38 (R-38 Ceiling Below Attic) |
| Walls | R-21+R5 CI, 2x6, Synthetic Stucco |
| Roof assembly | Asphalt Shingle, R-19 Below Deck, No RB, cool roof required |
| Radiant barrier | Not required |
| Window U-factor | U-0.30 |
| Window SHGC | 0.20 |
| Heating & cooling | Heat pump · HSPF2 9.0 / SEER2 18.5 / EER2 14.5 |
| Water heating | Heat-pump water heater (Tier 3 50-gallon HPWH) |
What this means for your Ontario design
In practice, walls go up at 2x6 with R-21 cavity insulation plus continuous-insulation sheathing on the outside, the roof needs a cool-roof finish (high solar reflectance) and skips the radiant barrier, windows must hit SHGC 0.20, meaning low-solar-gain glazing, the heat pump needs HSPF2 9.0 / SEER2 18.5.
ADUs, additions, and alterations in Ontario
Ontario is one of California's most active markets for accessory dwelling units, additions, and addition-with-alteration projects. Each scope follows the same CZ10 prescriptive baseline shown above, with scope-specific adjustments built into the flow:
- Newly constructed ADUs (detached) get full PV sizing per the §150.1(c)14 prescriptive table.
- Attached ADUs and additions are treated as additions to the existing residence and skip PV sizing per §150.2(a) .
- Alterations on a permitted residence run a focused alteration baseline; existing equipment (HVAC, water heater) is grandfathered unless you're replacing it.
Submitting your Title 24 report to City of Ontario Building Department
Your signed Title 24 report PDF (the CF1R) gets submitted alongside your permit drawings to City of Ontario Building Department. The CF1R is registered with the CHEERS residential energy compliance registry, California's state-approved registry for residential Title 24 reports. The registry assigns the certificate a unique ID that San Bernardino County plan-checkers verify when they review your submittal.
If City of Ontario Building Department returns a Title 24 correction on your plan-check letter, the plan-check response flow is built into the project dashboard, upload the correction letter and we'll analyze the cited items and route them to either a revised report or a restart, depending on what changed.
Your three design options
Ontario projects choose between three pathways: Prescriptive (matches the CZ10 baseline above), 2x4 Performance (lighter framing, compensated by upgraded windows, roof, and equipment), and 2x6 Enhanced (heavier framing, easier equipment specs). Full breakdown on the Title 24 explained page.
Title 24 reports in other California cities
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