Title 24 Insulation Requirements by Climate Zone
Minimum R-values for walls, roofs, floors, and ducts in California buildings
Last updated: April 3, 2026
Contents
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 2022 code cycle (effective January 1, 2023) increased R-value requirements in several climate zones compared to the 2019 cycle. The 2025 code cycle (effective January 1, 2026) continues tightening requirements, particularly for attic and wall insulation in inland and desert zones.
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.
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 table below shows typical ranges across California's climate zones.
| Component | Typical R-Value Range | Notes |
|---|---|---|
| Attic / Roof | R-30 to R-38 | Varies by climate zone; higher in inland/desert zones |
| Exterior Walls | R-13 to R-21 | Cavity insulation; some zones also require continuous insulation |
| Floors Over Unconditioned Space | R-19 to R-30 | Raised floors, floors over garages or crawl spaces |
| Slab Edge | R-7 to R-10 | Where required by climate zone |
| Ducts in Unconditioned Space | R-6 to R-8 | Applies to supply and return ducts outside the thermal envelope |
These values represent the prescriptive path. The actual requirement for your project depends on the climate zone where the building is located. For example, a home in Climate Zone 16 (mountainous areas with cold winters) will need R-38 attic insulation, while a home in Zone 7 (San Diego coast) may only need R-30.
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.
Roof Insulation
Nonresidential buildings typically require above-deck roof insulation in the range of R-20 to R-30, depending on the climate zone. Above-deck insulation is preferred because it creates a continuous thermal barrier without breaks at structural members. Metal buildings may use a combination of liner system insulation and above-deck rigid board.
Wall Insulation
Metal-framed walls in nonresidential buildings require continuous insulation on the exterior to offset the high conductivity of steel studs. The code specifies both cavity insulation (R-13 to R-19) and continuous insulation (R-3.8 to R-7.6) depending on the wall type and climate zone.
Watch out: Steel studs conduct heat roughly 400 times faster than wood. A metal-framed wall with R-19 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.
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.
Tip: Even on the performance path, there are mandatory minimum insulation levels that cannot be traded away. You cannot skip duct insulation entirely just because your windows are excellent. Check the mandatory measures table in Part 6 for the absolute minimums.
Frequently Asked Questions
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.