Title 24 Compliance for Multifamily Window Replacement

Most Title 24 explanations are written for new construction. A multifamily window replacement is an alteration, which has its own requirements, its own exceptions, and — since the start of 2026 — its own new numbers. This page covers what applies, where, and the one scheduling detail that catches phased projects.

What the current code requires

The 2025 Building Energy Efficiency Standards — California Code of Regulations Title 24, Part 6 — apply to buildings whose permit applications are submitted on or after 1 January 2026.

For replacing vertical fenestration, the prescriptive requirements are:

The change that matters here is the first row: the maximum U-factor in those zones dropped from 0.30 to 0.27. The California Energy Commission states it directly in its compliance manual for the 2025 standards — “for additions and alterations, the prescriptive maximum U-factor requirements for windows reduced from 0.30 to 0.27 in climate zones 1 – 5, 11 – 14, and 16; climate zones 6 – 10 and 15 remain at 0.30 U-factor.”

Which zone your building is in

This is the part that decides whether the change affects you, and across Northern California it almost always does:

Every one of these sits in the group that moved to 0.27. None is in zones 6 to 10 or 15, where 0.30 still applies. If your property is outside these markets, the Energy Commission publishes an address lookup tool and a climate zone list by ZIP code.

The exception for small work

Replacing 75 square feet or less of vertical fenestration may be done at a maximum U-factor of 0.40 and a maximum SHGC of 0.35. On a building-wide project this will not apply, but it does mean an isolated repair — a handful of openings after storm damage, say — is not held to the full alteration specification.

The prescriptive path is not the only path

The numbers above are the prescriptive route: meet each requirement individually and you comply. There is also a performance path, where the building is modelled and shown to perform at least as well overall. It costs more in engineering and it takes longer, but it exists so that a project with an unusual constraint is not forced into a product that does not suit it. If a specification you want misses the prescriptive figure, ask about the performance path before abandoning it.

The phasing trap

Compliance is fixed by when the permit application is submitted. On a single-project replacement this is a non-issue. On a community being replaced building by building across three or four budget years, it means an early phase and a late phase can be permitted under different code cycles — and therefore built to different window specifications.

The practical consequences are worth thinking about before phase one is designed:

• Matching. Different specifications can mean visibly different frames or glass tint across one property.
• Procurement. A specification locked for the whole project may become non-compliant for later phases.
• Budget. A later phase held to a tighter standard may cost more per opening than the one you budgeted from.

None of these are unmanageable, but all of them are cheaper to plan for than to discover. If a phased project matters to you visually or contractually, discuss permitting strategy with your contractor and your building department at the start. Our guide to phasing a window replacement across an occupied building covers the scheduling side.

How to check a window against the requirement

Both figures are on the NFRC label on the unit — U-factor and SHGC, as certified numbers. Confirm them against your zone rather than accepting a general assurance that a window is “Title 24 compliant”, since that phrase means nothing without the zone attached. Our guide to reading an NFRC window label covers what each figure means.

On permitting for replacement work specifically, see whether you need a permit for retrofit windows in California. For the regulation in general, our page on what Title 24 is covers the wider code.

Sources

The figures on this page come from the California Energy Commission: the 2025 Building Energy Efficiency Standards for the effective date, the Single-Family Residential Compliance Manual for the 2025 standards (CEC-400-2025-005) for the alteration requirements and exceptions under Section 150.2(b)1A, and the Commission’s Building Climate Zones by ZIP Code list for the zone assignments. Requirements change with each code cycle; confirm the current standard with your building department before specifying.

Working with Heritage Exteriors

We specify and install multifamily window replacements to current code across Sacramento, the Bay Area and Northern California, and we pull the permits as part of the project — CSLB #1055919. If you are planning a phased replacement and want the compliance question settled before the first building is designed, call (916) 546-2991.