§150.2(b) · Alterations to existing residences

# §150.2(b): Alterations to existing residences

What it requires

An "alteration" is work done on an existing residence that does NOT add conditioned floor area. The Title 24 framework is component-based: each specific component that you alter has its own trigger.

Common triggers:

• Replace the furnace or AC → the new equipment meets §150.1(c) for its category.
• Replace ≥ 50% of windows → the new windows meet §150.1(c) U-factor and SHGC for the climate zone.
• Replace the water heater → the new heater meets §150.1(c) (tier 3 or tier 4 HPWH for most CZs).
• Re-roof a roof in CZ10–15 → cool-roof per §110.10.
• Replace ≥ 40 linear feet of ductwork → new ducts meet §150.0(m) insulation + §110.7 leakage test.
• Add bedroom (regardless of CFA change) → whole-building ventilation rate has to be re-checked.

Untouched components stay grandfathered, they keep their original-permit code era.

When it applies

• Any work on an existing residence that doesn't add CFA.
• "Alteration only" projects.
• The existing-residence portion of an addition-with-alteration project (in parallel with §150.2(a) on the addition).

Key carve-outs

• No §150.1(c)14 PV mandate, alterations don't trigger solar PV regardless of scope.
• No envelope upgrade required on untouched components, leave walls alone, walls stay grandfathered.
• No HVAC upgrade required on untouched equipment.

How we use it

When you select "Alteration Only" or "Addition and/or Alteration" on the Confirm step:

• We list which components you're replacing (HVAC, DHW, windows, ducts) and apply §150.2(b) triggers only for those.
• Existing equipment that's NOT being replaced keeps its existing rating in the model.
• The CF1R notes "Existing, no change" on the rows for grandfathered components.

See the Add+Alt paths article for the full component-trigger table.