BoK Energy Design

§ 06 · TITLE 24 / 101

California Title 24,
explained.

A plain-English walkthrough of the code that decides whether your permit gets pulled.

CODE CYCLE

2025 California Energy Code

AUTHORITY

CA Energy Comm.

PART

Part 6 / Energy

EFFECTIVE

Jan 2026

READ TIME · ~12 MIN · LAST REVISED APR 2026

01

What Title 24 is

Title 24 is the Code of Regulations that governs how buildings get built in California. It's huge. Twelve parts covering everything from structural to accessibility. The piece you keep hearing about is Part 6: the California Building Energy Efficiency Standards. That's the energy code.

Part 6 sets a minimum energy performance for every new home, every addition, and a surprising number of alterations. It exists because California, as a matter of state policy, decided decades ago that the cheapest kilowatt-hour is the one you never burn. So instead of subsidizing more power plants, the state keeps tightening what new buildings are allowed to waste.

The code is updated on a three-year cycle. We are currently on the 2025 code, which became enforceable on January 1, 2026. Every permit pulled after that date follows the 2025 rules, regardless of when the project was designed.

02

Performance vs Prescriptive

There are two legal ways to prove a project complies. They are not equally useful, but both are real.

The prescriptive method

The prescriptive method is a checklist. You meet every single line item exactly: the specific R-value in the walls, the specific U-factor in the windows, the specific efficiency rating on the furnace, the specific duct-leakage target, the specific PV size. No modeling. No substitutions. If the code says R-30 ceilings in Zone 12, you install R-30 ceilings in Zone 12.

It's rigid by design. That rigidity is the trade: you get a faster paperwork path (a short prescriptive worksheet instead of a full model) in exchange for no flexibility to swap anything. Miss one line and you fail the whole path.

The performance method

The performance method models the entire house in CEC-approved software (usually EnergyPro or CBECC-Res) and proves that the total modeled energy use meets or beats a baseline version of the same house built to prescriptive minimums. That's the game: don't beat every line item, beat the sum.

Which means you can trade. Slightly worse windows for slightly better insulation. A nicer heat pump for a thinner wall assembly. More PV for less everything else. The model does the arithmetic and the compliance margin is what the plan-checker reads.

Prescriptive is a checklist. Performance is a budget. Real projects almost always want the budget.

The performance path is what we use on essentially every project. The only time prescriptive makes sense is when a project is already ultra-conservative: a cookie-cutter spec home with stock assemblies and zero design ambition.

03

What a CF1R contains

The CF1R (Certificate of Compliance, Residential) is the document. It's what gets stamped, registered, and stapled to your permit set. It's the receipt for the whole modeling exercise.

A CF1R includes, in rough order:

  • Project identification. Address, climate zone, square footage, orientation, number of stories, conditioned floor area.
  • Envelope. Every wall, ceiling, floor, slab, door, and window with its assembly, U-factor, SHGC, and area.
  • HVAC. Equipment type, efficiency ratings (SEER2, HSPF2, AFUE), duct location, duct leakage target.
  • Water heating. Type, size, efficiency, recirculation strategy if any.
  • PV & storage. Solar array size and, as of the 2025 code, battery storage details for most new construction.
  • Compliance margin. How much the modeled design beats the baseline, expressed in a few different metrics (TDV, EDR, LSCe).
  • Mandatory measures. A long checklist of things every home must include regardless of method (low-flow fixtures, LED lighting, etc.).
  • Required verifications. What the field rater will need to confirm after install.
CF1R-PRF-01PROJECT INFOENVELOPEHVACWATER HEATINGPV + STORAGECOMPLIANCE MARGINMANDATORY MEASURESREGISTEREDWhat you're buildingADDRESS · ZONE · AREAEvery assemblyU-FACTOR · R-VALUE · AREAMandatory PV2025 CODE · SIZE + BATTERYThe stamp & the IDCHEERS-REGISTERED
FIG. 01 · CF1R ANATOMY

§ 04 · THIRD-PARTY VERIFICATION

HERS is
now ECC.

Effective with the 2025 code on January 1, 2026, the program formerly called HERS (Home Energy Rating System) was renamed ECC, Energy Code Compliance. HERS Raters are now ECC Raters.

The job didn't change. Same function: an independent, third-party field tech visits the site, verifies that what was installed matches what got modeled, and registers the result. Duct leakage. Quality insulation installation. Refrigerant charge. Fan watt draw. If the model said 6% duct leakage, the ECC Rater has to measure 6% duct leakage.

Just a name change, but the kind that trips up contractors who haven't renewed their vocabulary yet. If your GC says "the HERS guy," they mean the ECC Rater. Same person.

ARCHITECTDRAWS PLANSBOMODELS + CF1RCHEERSREGISTERSPLAN-CHECKAPPROVESCONTRACTORINSTALLS + CF2RECC RATERVERIFIES + CF3RFINALPERMIT CLOSEDPHASE · DESIGN + PERMITPHASE · CONSTRUCTION + CLOSE-OUT
FIG. 02 · WHO TOUCHES THE REPORT, AND WHEN
05

CHEERS, the registry

Every CF1R has to be registered with a CEC-approved data registry before plan-check will accept it. In California there are a handful of these registries; the one we use is CHEERS, California Home Energy Efficiency Rating Services.

CHEERS is also an approved ECC Provider, which is the entity that credentials the field raters. For the homeowner it functions more like a notary: the report gets uploaded, assigned an ID, and locked. Plan-check downloads it from there, not from an email attachment, which is why an unregistered PDF isn't useful to anyone.

The registry charges a small per-report fee, typically $7 to $32 depending on project type. We bundle that into the flat $300, so you won't see it as a separate line item.

06

California's 16 climate zones

Title 24 does not treat California as one place. It is divided into 16 climate zones, each with its own baseline assumptions for heating degree days, cooling load, solar exposure, and ventilation.

A wall that passes in Zone 3 (Bay Area, mild, foggy) might need an inch more rigid insulation to pass in Zone 12 (Sacramento Valley, hot summers, cold-ish winters) and a totally different assembly to pass in Zone 14 (high desert, brutal on both ends) or Zone 16 (mountain, snow load, serious heating).

Zone boundaries follow county and sub-county lines, not elevation contours, which means a house in a coastal valley and a house on a ridge five miles away can sometimes technically share a zone and produce wildly different modeled loads anyway. The software handles that. The zone is just the starting point.

The full map, with every zone labeled, is below.

§ 05 · CLIMATE ZONES

All sixteen.
Coast to Mammoth.

California’s energy code treats every region differently. What passes in Zone 3 flunks in Zone 14. BoK Design has modeled projects across every one of them. Select a zone to see the typical character.

HOVER OR TAP A ZONE · SIXTEEN CALIFORNIA CLIMATE ZONES

NOW VIEWING

CZ 12

Sacramento Valley

CENTRAL VALLEY

Sacramento · Davis · Stockton

THE FIGHT

Hot summers, cool winters. The common-case zone.

CODE
2025 · T24 · PART 6
METHOD
PERFORMANCE
SOFTWARE
ENERGYPRO
REGISTRY
CHEERS · ECC
07

What triggers a report

The short list of things that require a Title 24 compliance report:

  • Any new residential construction. Single family, duplex, ADU, JADU, multi-family up to three stories: all residential low-rise. No exceptions.
  • Most additions. Once the added conditioned space crosses roughly 100 ft², you'll generally need a report. Smaller additions sometimes escape, but many jurisdictions still ask.
  • HVAC replacement. A like-for-like furnace swap can be a simple alteration form, but any change in system type, especially going from gas to heat pump, almost always triggers a full CF1R.
  • Window replacement above a certain area-fraction of the envelope.
  • Re-roofs in certain climate zones, where cool-roof requirements apply.
  • Major envelope work. Residing, re-insulating, opening up walls. Usually pulls in at least an alteration-scope report.
08

How much it costs

We charge a single flat rate, on purpose.

CF1R report, per dwelling unit

INCLUDES CHEERS REGISTRATION

$300

Client-requested revision

DESIGN CHANGE, PRODUCT SWAP, SCOPE CHANGE

$100

Plan-check pushback (our error)

FREE. WE FIX IT.

$0

No hourly billing. No retainer. No "complexity upcharge" on a normal single-family project. For a duplex, triplex, or small multi-family, it's $300 per dwelling unit, which is how the code treats them anyway.

Turnaround is 1–3 business days on a typical project from the moment we have enough plan information to model. Rush work happens; ask.

09

What happens at plan-check

Once the CF1R is registered, it gets submitted alongside the plan set. City or county plan-check reviews both together. Four things can happen:

  1. Clean approval. The most common outcome. Permit goes through. Next step is the field install and the ECC Rater visit.
  2. Clarification request. Plan-check questions something on the CF1R, usually a mismatch between what's drawn and what's modeled (different window count, missing skylight, etc.). Forward the comment to us; we turn it the same day in most cases.
  3. Design change required. Plan-check wants the project itself to change: more PV, better U-factor, a different water heater. The architect decides what to change; we re-model and re-issue.
  4. Rejection. Rare when the report was written correctly. Usually means the prescriptive path was attempted on a project that should have been modeled.

The revision is not a bug. It is how the feedback loop between designer, modeler, and plan-checker was designed to work.

10

Common misunderstandings

MYTH

"An ADU doesn't need Title 24."

ACTUALLY

It almost always does. Detached ADUs are brand-new residential construction and require a full CF1R. Attached and conversion ADUs usually count as additions or alterations, which also trigger a report. The only reliably exempt case is a conversion of existing conditioned space with zero envelope or system changes, which is rare in practice.

MYTH

"The prescriptive path is cheaper."

ACTUALLY

It's cheaper in paperwork, and more expensive in materials, sometimes dramatically so. The performance method routinely saves thousands of dollars in build cost because you can trade nicer HVAC for thinner walls, or more PV for simpler glazing. The extra model-hours pay for themselves on most projects.

MYTH

"CF1R, CF2R, CF3R, same thing, right?"

ACTUALLY

No. CF1R is the design-phase compliance report, signed by the modeler. CF2R is the installation certificate, signed by the installing contractor after work is complete. CF3R is the verification certificate, signed by the ECC Rater after field testing. Three different documents, three different signers, three different phases.

MYTH

"I can just use last year's report."

ACTUALLY

A CF1R is tied to a specific project, specific plan set, and specific code cycle. The 2025 code introduced heat pump prescriptive baselines for both space and water heating, new battery storage requirements, and tightened climate-zone baselines. A 2022-cycle report will not pass a 2026 plan-check.

MYTH

"Gas furnace is fine, everyone uses gas."

ACTUALLY

Under the 2025 code, the prescriptive baseline for most climate zones is a heat pump, for both space conditioning and water heating. You can still install gas, but you'll need to make up the efficiency difference elsewhere in the model. The math is harder every cycle.

§ END · STILL CONFUSED

Still confused?
That's the job. Ask us.

This page covers the code at about a thousand feet up. Every real project has details that only make sense on the phone. Send the plan set. She'll tell you what path, what it costs, and when it's done.

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