Title 24 Insulation Requirements by Climate Zone

Minimum R-values for walls, roofs, floors, and ducts in California buildings

Last updated: May 23, 2026

Overview What Changed in 2025 Residential Requirements Nonresidential Requirements Climate Zones Compliance Paths Related Resources FAQ Products

Overview

California Title 24, Part 6 (the Energy Code) sets minimum insulation requirements for every new building and most major renovations in the state. Insulation is one of the most cost-effective ways to reduce energy use, and the code treats it accordingly. If you are building or remodeling in California, you need to know what R-values the code requires for your climate zone.

The 2025 Energy Code is in effect today for any building permit applied for on or after January 1, 2026. The prior 2022 cycle still applies to projects whose permit was filed before that date. The 2025 cycle tightened envelope requirements compared to 2022 — most notably, cathedral ceilings now require R-38 in all 16 climate zones, the prescriptive wall cavity floor was raised (2×4 walls require R-15 minimum, 2×6 walls require R-21 minimum), and vertical fenestration U-factors were lowered in cooler and inland zones. Statewide minimums always apply; local reach codes may exceed them but cannot drop below.

Key point: Title 24 insulation requirements vary by climate zone, building type (residential vs. nonresidential), and building component (roof, wall, floor, duct). There is no single statewide R-value. Always check the requirements for your specific project location.

What Changed in the 2025 Cycle

Most 2022-cycle insulation requirements carry forward into 2025, with these material changes for residential and low-rise multifamily envelopes:

Component	2022 Cycle	2025 Cycle
Cathedral ceiling	Zone-dependent	R-38 all 16 zones
2×4 wall cavity (minimum)	Often R-13 acceptable	R-15 minimum
2×6 wall cavity (minimum)	Often R-19 acceptable	R-21 minimum
Vertical fenestration U-factor	≤ 0.30	≤ 0.27 in zones 1–5, 11–14, 16
Nonresidential envelope (Table 140.3-B)	Per cycle	Maximum U-factors reduced for many assemblies and zones
Quality Insulation Installation (QII)	Required on prescriptive path	Required on prescriptive path (no change)

Plan ahead: Cathedral assemblies and 2×6 walls that scraped by under the 2022 cycle won't meet 2025 prescriptive minimums. For active 2022-cycle permits, the older values still apply; for any new permit application this year, design to the 2025 minimums or use the performance path with mandatory-measures floors.

Residential Requirements

For low-rise residential buildings (single-family homes, duplexes, townhomes, and multifamily buildings up to three stories), Title 24 prescribes minimum R-values for each building component. The tables below show the prescriptive values for all 16 California climate zones, anchored to Table 150.1-A of the Energy Code.

Residential ceiling / attic insulation by climate zone

Climate Zone	Duct Option B (ducts in attic)	Duct Option C (ducts in conditioned space)
1	R-38	R-38
2	R-38	R-30
3	R-30	R-30
4	R-30	R-30
5	R-30	R-30
6	R-30	R-30
7	R-30	R-30
8	R-38	R-30
9	R-38	R-30
10	R-38	R-30
11	R-38	R-38
12	R-38	R-38
13	R-38	R-38
14	R-38	R-38
15	R-38	R-38
16	R-38	R-38

Source: California Energy Code Part 6, Table 150.1-A. Cathedral ceilings require R-38 in all 16 zones under the 2025 cycle.

Other residential prescriptive insulation

Component	Climate Zones	Minimum
Wood-framed wall (above grade)	1–5, 8–16	U-0.048 assembly — typical: 2×6 R-21 cavity + R-5 continuous, or 2×4 R-15 cavity + R-10 continuous
Wood-framed wall (above grade)	6 and 7	U-0.065 assembly — typical: 2×4 R-15 cavity, no continuous required
Raised floor over unconditioned space	All zones	U-0.037 (≈ R-19 batt)
Slab edge insulation	Zone 16 only	R-7, 16" deep
Slab edge insulation	All other zones	Not required (NR)
Duct insulation in unconditioned space	1, 2, 8–16	R-8
Duct insulation in unconditioned space	3–7	R-6
Duct insulation in conditioned space	All zones	Not required when the duct system is entirely within conditioned space and verified per §150.0(m)1B

2025 cycle minima. The wall U-factor target is unchanged from 2022, but the cavity-only path now requires R-15 (2×4) or R-21 (2×6). The continuous-exterior path remains the simplest way to hit U-0.048 in most assemblies.

These values are the prescriptive path. The actual requirement for your project depends on the climate zone where the building is located AND the duct compliance option (Option B = ducts in attic, Option C = ducts in conditioned space). Quality Insulation Installation (QII) inspection is required on the prescriptive path for new homes and additions greater than 700 sq ft in all 16 zones — plan for a HERS-rater visit before drywall.

Continuous insulation on the exterior side of wall framing is increasingly required in colder climate zones. This addresses thermal bridging through wood or steel studs, which can reduce the effective R-value of a wall assembly by 20% or more.

Nonresidential Requirements

Commercial buildings, high-rise residential (four stories and above), and other nonresidential projects face higher insulation requirements than low-rise residential. The code is especially strict about metal-framed buildings, which have significant thermal bridging if not addressed with continuous insulation.

Use Table 140.3-B in the Energy Code for permit-grade values. The ranges below show typical 2025-cycle prescriptive minima across California's 16 climate zones. For a specific cell, consult §140.3 directly or use CBECC-Com 2025 to generate the reference-design envelope. Nonresidential prescriptions are stated as maximum U-factors; the equivalent R-values listed here are typical assembly compositions.

Assembly	Typical Compliance Approach
Roof, above-deck insulation (low-slope)	Continuous rigid insulation above the deck; assembly typically R-20 to R-30 depending on climate zone
Metal-framed wall	Cavity insulation (R-13 to R-19) paired with continuous exterior insulation (typically R-7.5 ci) to offset stud thermal bridging
Wood-framed wall	Cavity insulation (R-13 to R-21), with continuous insulation added where needed to meet zone-specific U-factor
Mass wall (HC ≥ 7.0 Btu/ft²·°F)	Continuous insulation on the exterior face; required value drops significantly in hotter zones
Floor over unconditioned space (steel-framed)	Cavity + continuous insulation; assembly typically R-19 to R-30 depending on climate zone

Numeric U-factor and R-value cells per climate zone are in Table 140.3-B of the 2025 Energy Code. Pull them from the official CEC code text or CBECC-Com 2025 before specifying for permit — values vary by zone, building type, and assembly category.

Watch out: Steel studs conduct heat roughly 400 times faster than wood. A metal-framed wall with R-21 batt insulation between studs may only perform at R-7 to R-9 effective. Continuous exterior insulation is the fix, and the code now requires it in most climate zones for nonresidential metal-framed walls.

Climate Zones

California uses 16 climate zones to set energy code requirements. Each zone reflects a distinct combination of temperature, humidity, wind, and solar radiation. Insulation requirements track closely with heating and cooling loads.

California Energy Commission's online tool (energy.ca.gov, search "California climate zones") confirms a project's zone by ZIP code. Some ZIPs span multiple zones — when in doubt, the project address is authoritative.

Coastal Zones (1-3)

Mild year-round temperatures mean lower insulation requirements. These zones cover cities like Arcata (Zone 1), Santa Rosa (Zone 2), and San Francisco (Zone 3). Heating and cooling loads are relatively modest, so the code allows lower R-values in most assemblies.

Moderate Zones (4-9)

These zones cover much of the populated coast and near-coast, including Los Angeles (Zone 9), San Jose (Zone 4), and Santa Maria (Zone 5). Requirements are moderate, with some zones starting to require continuous wall insulation.

Inland and Desert Zones (10-15)

Hot summers and cool winters push insulation requirements higher. Sacramento (Zone 12), Fresno (Zone 13), and desert areas like Palm Springs (Zone 15) all fall in this group. Attic insulation requirements are at their highest here, and continuous wall insulation is commonly required.

Mountain Zone (16)

The coldest zone in California, covering mountain communities like Truckee and Big Bear. Heating loads dominate, and the code requires the highest R-values for roofs, walls, and floors. This is the only zone where slab-edge insulation is required for most residential projects.

Tip: Check your project's climate zone at the California Energy Commission website before specifying insulation. Climate zone boundaries do not always follow city or county lines, and a project just a few miles from a zone boundary can have different requirements.

Compliance Paths

Title 24 offers two main paths to demonstrate compliance with insulation requirements. Most residential projects use the prescriptive path because it is simpler. Larger or more complex projects often benefit from the performance path.

Prescriptive Path

The prescriptive approach is straightforward: look up the required R-values for your climate zone and building type, install insulation that meets or exceeds those values, and document it on the compliance forms. There is no energy modeling involved. Each component (roof, walls, floors, ducts) must independently meet its prescribed R-value.

Performance Path

The performance approach uses approved energy modeling software (such as CBECC) to calculate the building's total energy use. The model compares your proposed design against a standard reference design. As long as the proposed building uses less energy than the reference, it passes.

This allows tradeoffs. For example, if you install high-performance windows and an efficient HVAC system, the model might show that you can use slightly less wall insulation and still meet the overall energy budget. Conversely, more insulation can offset a less efficient mechanical system.

Mandatory Minimums (Cannot Be Traded Away)

Even on the performance path, some measures are mandatory floors that no amount of HVAC upgrade or PV oversize can offset. These include minimum ceiling insulation under §150.0(a), wall insulation under §150.0(c), raised-floor insulation under §150.0(d), minimum HVAC efficiencies, envelope air-sealing and duct-sealing with HERS verification, mechanical ventilation per ASHRAE 62.2, demand-responsive thermostats, and PV / battery readiness where applicable. The performance path lets you trade above the floor, never below it.

Tip: When in doubt, check §150.0 for the mandatory floor before you propose a tradeoff on the performance path. A common pitfall is reducing wall cavity insulation below R-15 (2×4) or R-21 (2×6) — those are mandatory minima in 2025, not just prescriptive targets.

Frequently Asked Questions

What climate zone is my project in?

California has 16 climate zones defined in Reference Joint Appendix JA1 of the Energy Code. Zones are tied to CEC reference weather stations — not city limits — so a single municipality may span multiple zones. The California Energy Commission publishes an official ZIP-code and address lookup tool at energy.ca.gov; for a project near a zone boundary, the building department's written determination is authoritative. Representative zones for some common reference weather stations: San Francisco (Zone 3), LAX area (Zone 6), San Diego International area (Zone 7), Long Beach area (Zone 8), Hollywood Burbank / San Fernando Valley (Zone 9), Riverside / inland LA basin (Zone 10), Sacramento (Zone 12), Fresno (Zone 13), Palm Springs (Zone 15), Truckee / mountain communities (Zone 16).

Does the 2025 cycle apply to my permit?

Yes if your permit application was filed on or after January 1, 2026. Permits filed before that date can stay on the 2022 cycle through completion. Local jurisdictions cannot drop below the state minimum and cannot keep applying the 2022 cycle to new applications after January 1, 2026. Some cities adopt local reach codes that exceed the state minimum — confirm with the local building department.

Does Title 24 insulation apply to remodels?

Yes, if you are altering the building envelope. When you open up walls for a remodel, add a room, or replace more than 50% of the roof, the altered components must meet current Title 24 insulation requirements. Minor repairs and cosmetic work generally do not trigger the requirement, but any project that requires a building permit and involves the envelope will.

Can I use spray foam to meet the insulation requirement?

Yes. Closed-cell spray foam is a popular choice because it delivers a higher R-value per inch (roughly R-6 to R-7 per inch) compared to fiberglass batts (R-3.2 to R-3.8 per inch). It also acts as an air barrier, which improves overall envelope performance. Open-cell spray foam (about R-3.7 per inch) is another option but requires a vapor retarder in some climate zones. Both types are accepted under Title 24 as long as the installed R-value meets the requirement for your climate zone.

What if my climate zone has different requirements than what I found online?

Always verify against the current code cycle for your specific zone. Online references (including this page) provide general guidance, but the code is updated every three years and requirements shift between cycles. The official source is the California Energy Commission website, which publishes the current prescriptive tables. Your local building department can also confirm which code cycle is in effect for your permit.

Do ducts inside conditioned space need insulation?

Ducts that run entirely within the conditioned (heated and cooled) space of a building generally do not need insulation under Title 24, because there is minimal temperature difference between the duct and the surrounding air. Ducts in unconditioned spaces like attics, garages, and crawl spaces must be insulated to R-6 or R-8, depending on the climate zone, to prevent energy loss.