Climate Zones 8, 9, and 10 cover the wedge of Southern California that runs from Long Beach and the LA basin inland through Anaheim, Riverside, and the near Inland Empire. The 2025 Energy Code is meaningfully stricter on summer cooling here than the 2022 cycle, so we've tightened our Title 24 baseline for all three zones. If your project is in one of these zones, the compliance verification already uses these values — this note is so the windows and equipment on your plans match.

What to spec

  • All three zones — windows at SHGC 0.20 or lower. Solar-control (Low-E) glass is the headline change. Most current Low-E coatings meet this comfortably; the field issue is older inventory still spec'd to the 2022 baseline of 0.23.
  • CZ8 and CZ9 — cooling at SEER2 20 / EER2 15 on the upgraded design options (Balanced and High-Performance).
  • CZ10 — cooling at SEER2 18.5 / EER2 14.5 on the High-Performance option specifically. CZ10's High-Performance wall is a bit thinner, so it needs a little more cooling headroom to land comfortably in compliance.

What designers should adjust

1. Window schedule — west and south faces at SHGC ≤ 0.20. Those sun-exposed elevations drive the cooling load. Spec'ing the same glass on every face is usually simpler than splitting the schedule. 2. Call the cooling tier on the schedule, not a model. "SEER2 ≥ 20 / EER2 ≥ 15" (or the CZ10 High-Performance numbers) lets the contractor pick any qualifying unit. Pinning a model on the plans is what creates substitution friction. 3. Don't over-spec the Standard option. On the Standard (prescriptive) pathway, the new SHGC value is enough on its own — the cooling-tier bump only applies to the upgraded options.

A note on equipment availability

SEER2 18.5–20 with EER2 14.5–15 is comfortably within the mid-tier inverter-driven split-system catalog from Mitsubishi, Daikin, LG, and Carrier — the procurement story is essentially unchanged from prior years. If a contractor pushes back on the tier, the right move is to specify the efficiency on the report and let them choose the model.

What did not change

Neighboring coastal CZ7 (coastal San Diego) keeps its prior baseline — the coastal envelope and mild day-to-night swing keep its cooling load manageable, so it doesn't need the same tightening. If you work across the CZ7 / CZ10 line, note that the window-SHGC requirement differs between them.