What changes between options
All three pathways meet Title 24 Part 6 by different trade-offs. The prescriptive pathway follows Table 150.1-A literally — wall, ceiling, window, and HVAC values are set by the code itself. The two alternative pathways re-balance the envelope-vs-mechanical trade in ways most California builders find easier to construct.
Prescriptive
Code-minimum baseline. Walls include continuous-insulation sheathing where the table prescribes it (R-15+R4 CI on 2x4, R-21+R5 CI on 2x6). Best when the project budget already includes CI and the team is set up to detail it correctly.
2x4 Performance (HPE)
Familiar 2x4 R-15 wall framing with no continuous insulation. The wall delta is carried by a Tier 4 HPWH (always) plus the climate zone's prescriptive heat-pump efficiency. Common pick for ADUs and tighter detached residences.
2x6 Enhanced (Hybrid)
2x6 R-21 wall framing with no continuous insulation. Wall mass plus the climate zone's prescriptive HVAC and HPWH carry compliance. A popular middle ground for larger SFRs where the 2x4 path leaves insufficient headroom.
Per-zone differences also flow through both alternatives — for instance, the cooling-dominant zones (CZ8–CZ12) prescribe a more aggressive SHGC and heat-pump cooling tier, while the heating-dominant alpine zone (CZ16) prescribes a higher HSPF2 minimum. Those baseline values are inherited by the 2x4 and 2x6 pathways, so picking your zone first is the right way to evaluate the trade-offs.
Browse all 16 zones
CZ1 · CZ2 · CZ3 · CZ4 · CZ5 · CZ6 · CZ7 · CZ8 · CZ9 · CZ10 · CZ11 · CZ12 · CZ13 · CZ14 · CZ15 · CZ16