Every California residential project chooses one of two compliance paths. It's the first real decision on a Title 24 report, and it quietly determines what the rest of the paperwork looks like: how much flexibility you have, what trade-offs the code lets you make, and how a plan-check reviewer evaluates the result.
The two paths are the prescriptive method and the performance method. Both end at the same place: a stamped CF1R that the building department accepts. But they get there very differently.
The prescriptive method
Prescriptive compliance is a checklist. The California Energy Commission publishes a package of minimum requirements for every climate zone: R-values for walls and attics, U-factors for windows, HVAC efficiency minimums, water-heating requirements, photovoltaic array sizing, and a short list of mandatory measures.
If your house meets every single line on that list, you comply. There is no model, no score, and no trading.
The appeal is obvious. The documentation is lighter, the math is mostly subtraction, and a sharp contractor can read the spec sheet and match it without needing to look at the model. When it works, prescriptive is the faster, cheaper path.
It works for a narrow set of projects:
- Small additions where the addition-only scope matches the baseline spec exactly.
- New homes on a tight budget where every assembly and every appliance is already at or above the prescriptive minimums, because the design has no custom ambition.
- Developer tracts where the baseline package has already been value-engineered and the plans are cloned across twenty lots.
Where prescriptive breaks
The prescriptive path has no flexibility. If your window-to-floor ratio is higher than the code assumes, you fail, even if you make it up elsewhere. If you want a gas range in a climate zone where the baseline expects full electrification, you fail. If you want to size the photovoltaic array to the owner's electric-vehicle load instead of the house load, the prescriptive path doesn't care. You fail.
Custom homes almost always have at least one line on the checklist they can't hit cleanly. The 2025 code made this sharper: the prescriptive baseline for new construction now assumes a heat pump for both space heating and water heating. Any deviation (any gas furnace, any tankless water heater) is an automatic failure of the prescriptive path.
That is where performance comes in.
The performance method
Performance compliance runs the whole house through an energy model (in California, that model is EnergyPro) and produces a compliance score. The score your design produces is compared to the score a prescriptive baseline of the same house would produce. If your design is at least as good as the baseline, you comply.
That single sentence is the reason performance exists. It lets you trade. If your windows are worse than the baseline, your wall insulation can be better. If you want a gas furnace instead of a heat pump, a bigger photovoltaic array can make up the difference. If your glazing is bigger than the prescriptive assumes, a better-shaded orientation or a higher-performance window can balance the books.
The performance path sees the whole house as one energy system and asks only that the total comes out no worse than baseline. It is how custom homes are almost always documented, and it is how the 2025 code's more aggressive baseline becomes workable for real projects.
What performance unlocks
A few trade-offs that come up on nearly every project:
- Keeping a gas cooktop. The 2025 baseline is fully electric. Performance lets you keep gas cooking by offsetting it with a tighter envelope, a better water heater, or more photovoltaic.
- Oversized glazing. Modern houses have much more glass than the prescriptive package assumes. Performance lets a larger glazing area pass if the windows themselves perform well, or if the rest of the envelope is tighter.
- Photovoltaic trade-offs. If the roof can't take the prescriptive-sized array (wrong orientation, too much shade, historic overlay), performance lets you document what the roof can actually hold, with the rest of the house compensating.
- Heat-pump sizing flexibility. Prescriptive assumes specific efficiency minimums. Performance lets you substitute a more efficient unit in one place for a different system somewhere else.
- Batteries and smart panels. The 2025 code gives credit for battery storage. That credit is only accessible through performance modeling.
Why our office runs performance on every project
We write performance reports for every project: new construction, additions, alterations, ADUs, duplexes. A few reasons for the policy.
First, the performance path is the only way to represent a custom home honestly. Prescriptive pretends every house is the same house; performance actually looks at yours. The model includes the real geometry, the real orientation, the real windows, and the real systems.
Second, performance reports survive design change better. A change to the window package or the HVAC spec doesn't blow up the compliance. It gets re-run, and the model tells us whether we still pass or whether we need to adjust something else to stay passing. On a prescriptive report, a spec change can wipe out the whole path.
Third, the deliverable is the same permit-ready document. The CF1R from a performance run looks identical to the CF1R from a prescriptive run, from the plan-check reviewer's perspective. You do not pay for the flexibility at the counter. You pay for it only in the modeling time, which is our job.
The prescriptive method is a good path for the right project. On anything with ambition (on anything that could be called a custom house) the performance method is the one that lets the design decide, and lets the compliance report follow.