# §150.1(b): The performance compliance path
What it is
§150.1(b) defines the alternative to the prescriptive package. Instead of meeting every line item in §150.1(c), the designer models the proposed building in the Title 24 compliance engine and demonstrates it uses no more annual TDV (Time-Dependent Valued) energy than a "standard design" built to the §150.1(c) prescriptive package for the same climate zone, footprint, and orientation.
Two metrics get compared, both must pass:
- Total source energy — the TDV-weighted annual kBtu of the proposed design must be ≤ that of the standard design.
- Source energy efficiency — a per-end-use comparison that the compliance engine emits on the report.
If the proposed design wins both metrics, the project complies via §150.1(b) even when individual prescriptive line items (wall R-value, ceiling R-value, window U-factor) fall below the §150.1(c) target.
When a designer chooses it
- CI sheathing is value-engineered out. §150.1(c)1 requires R-4 or R-5 continuous insulation. If the project drops it, performance has to buy back the loss with better HVAC, DHW, or windows. Our Hybrid option works exactly this way.
- Architectural windows. Heavily glazed designs that fail the §150.1(c) prescriptive U-factor or SHGC can pass performance by tightening other components.
- Bonus envelope. When the project has a tighter envelope than prescriptive, the performance path lets the designer downgrade HVAC tier and save equipment cost while still complying.
Mandatory measures (§110.x) are NOT tradeable on the performance path — they're floors regardless.
How we use it
All three of our design options sit on the compliance spectrum:
- Prescriptive — meets §150.1(c) line-by-line.
- High-Performance Envelope — tightens R-values and drops cooling tier; performance path under §150.1(b).
- Hybrid — drops CI sheathing, buys it back with equipment; performance path under §150.1(b).
The Title 24 compliance verification report shows the §150.1(b) compliance margin (proposed kTDV vs standard kTDV) for the two non-prescriptive options.
Common gotchas
- Designers thinking they can trade a mandatory measure on the performance path — they can't, §110.x is the floor.
- Adding glazing area without compensating envelope or equipment upgrades — performance margin shrinks fast, and a project that passed at 25% WWR fails at 35%.
- Performance compliance computed for a 2030 climate model when the AHJ is on 2022 climate inputs — the rule cycle matters and the project must use the climate file referenced by the current code cycle.