California’s insulation rules sit in Title 24, Part 6, the Energy Code. Projects with permit applications filed on or after January 1, 2026 must follow the 2025 Energy Code. The exact R-value you need depends on your climate zone, your building type and whether the work is new construction, an addition or an alteration. This guide walks through each of those, then covers spray foam rules, inspections and how to plan a compliant job.
TL;DR
- The 2025 Energy Code applies to permit applications filed on or after January 1, 2026, and covers new buildings, additions and alterations, but not repairs.
- For new single-family homes, the prescriptive roof/ceiling requirement is R-38 in Climate Zones 1 and 11 to 16, and R-30 in Climate Zones 2 to 10.
- Spray foam must be certified in California, and compliance calculations use default values of 3.6 R per inch (open-cell) and 5.8 R per inch (closed-cell) unless the product is listed for more.
- Many projects need third-party verification of the insulation installation, so the installer and the paperwork matter as much as the product.
Table of Contents
- Which code cycle applies to your project
- When Title 24 applies: new builds, additions and alterations
- Climate zones: why the numbers differ
- Single-family prescriptive requirements
- Multifamily and nonresidential requirements
- Spray foam and the Energy Code
- Inspection and verification: Quality Insulation Installation
- A practical path to compliance
- Perspective
- What it costs: our published ranges
- Get your insulation job code-ready
- FAQ
- Sources
Which code cycle applies to your project
The California Building Standards Commission adopts a new Title 24 every three years. The 2025 State Code was released to cities in July 2025 and takes effect January 1, 2026. The Energy Code follows the same three-year cycle as the rest of the building code.
The trigger is the date your permit application is filed, not the date construction starts. If you applied before January 1, 2026, the earlier cycle governs your permit. If you are applying now, plan for the 2025 rules.
The Energy Code offers two ways to comply. A prescriptive option lets builders use methods known to be efficient. A performance option gives freedom in design as long as the building matches the overall efficiency of an equivalent prescriptive building. Mandatory measures apply to every building regardless of path.
The CEC also published a restructured version of the 2025 Energy Code with renumbered sections. It is for information only and is not the official regulatory document, so confirm section numbers against the adopted code when you prepare plans.
When Title 24 applies: new builds, additions and alterations
The Energy Code applies to additions and alterations, but not to repairs. An addition increases the conditioned floor area and volume of an existing building. An alteration, if it is not an addition, changes the water-heating, space-conditioning, lighting or electrical system, or the building envelope.
For insulation, that distinction matters:
- New construction: the full prescriptive package or a performance calculation applies.
- Additions of 700 square feet or less: roof and ceiling insulation in a ventilated attic must reach an overall assembly U-factor of 0.025 (R-38 in wood framing) in Climate Zones 1, 2, 4 and 8 to 16, or 0.031 (R-30 in wood framing) in Climate Zones 3 and 5 to 7.
- Larger additions: these are held to stricter requirements, and Quality Insulation Installation (covered below) comes into play for additions over 700 square feet.
- Alterations to the envelope: if you open up walls or replace roofing, expect the insulation rules for that assembly to apply to the part you touch.
The exact trigger for your scope is a plan-check question. Your city or county building department makes the call, and cities may amend the state code to be more restrictive when they find local climate, geologic or topographic conditions justify it. Always confirm local amendments before you finalize a design.
Climate zones: why the numbers differ
California is split into 16 climate zones, and the Energy Code is tailored to each. Performance budgets vary by zone and building type, and prescriptive packages work like a checklist. Your zone depends on your address, so look it up on the CEC’s climate zone resources or ask your designer before you pick an insulation product.
Single-family prescriptive requirements
The prescriptive path for new single-family homes runs through Table 150.1-A. The headline values:
| Assembly | Requirement | Where it applies |
|---|---|---|
| Roof/ceiling (wood framing) | U-0.025 (R-38) | Climate Zones 1 and 11 to 16 |
| Roof/ceiling (wood framing) | U-0.031 (R-30) | Climate Zones 2 to 10 |
| 2x4 walls | U-0.065 (R-15+4 or R-13+5) | Per table |
| Raised wood floors | U-0.037 (R-19) | Per table |
| Slab perimeter | U-0.058 (R-7.0) | Climate Zone 16 only |
The 2025 cycle also added a new prescriptive cathedral ceiling option in some publications’ summaries, but confirm that detail against the adopted code before you design to it.
The 2025 code lowered the prescriptive U-factor for roofs and ceilings, and for several wall types, by the equivalent of an additional R-2 of continuous insulation. That is the nonresidential change documented in the 2025 Nonresidential Compliance Manual, so use the current manual for commercial projects.
What U-factor means in practice
A U-factor measures how much heat passes through a whole assembly. Lower is better. R-value is its inverse for a given layer. Code tables often list a U-factor target and an R-value that typically meets it in wood framing, but your actual assembly includes framing, sheathing and finishes. That is why a designer or energy consultant checks the full assembly rather than just the label on the insulation.
Multifamily and nonresidential requirements
Multifamily buildings are covered by Section 170.2 (prescriptive) and Section 160.1 (mandatory). Under Table 170.2-A, Option B ceiling insulation is R-38 in Climate Zones 1, 2, 4 and 8 to 16 and R-30 in Climate Zones 3 and 5 to 7, with a radiant barrier required in Climate Zones 2, 3, 5, 6 and 7. Framed walls rated one hour or less must reach U-0.051 in most zones and U-0.065 in Climate Zones 6 and 7.
For nonresidential buildings, Section 120.7(a) sets a weighted average U-0.098 for metal building roofs and U-0.075 for wood-framed and other roof assemblies. Commercial owners should have the envelope designed with those figures in mind, particularly when re-roofing or converting space.
Spray foam and the Energy Code
Spray polyurethane foam has its own rules, and they are straightforward when you know them:
- Product certification. SPF must be certified by the Department of Consumer Affairs, Bureau of Household Goods and Services under Title 24, Part 12.
- Default R-values. Compliance calculations use 3.6 R per inch for open-cell and 5.8 R per inch for closed-cell foam. Products that exceed those defaults are listed in the Bureau’s registry.
- Verification. A HERS Rater must verify the SPF installation whenever you claim R-values above the defaults.
- Fire safety. All insulation must meet the flame spread and smoke density requirements of the California Building Code.
- Air sealing. Joints and openings that leak air must be sealed under Section 110.7, including roof penetrations, pipes, conduits, ducts and vents.
Air sealing is where spray foam earns its place on code projects. Foam insulates and seals in a single application, so one crew handles two code requirements. If you want a deeper look at how air sealing and insulation work together on permits, see our practical guide to passing Title 24 with air sealing and insulation.
Urea formaldehyde foam is a separate, restricted case. Section 110.8(b) allows it only in exterior side walls, and only with a 4-mil polyethylene vapor retarder between the foam and the interior space.
Open-cell or closed-cell for code work
Because closed-cell foam carries a default of 5.8 R per inch, it reaches a given R-value in less depth than open-cell at 3.6. That helps in tight assemblies such as 2x4 walls or shallow roof framing. Our comparison of closed-cell and open-cell spray foam covers cost and R-values in detail. Compared with other materials, see our pages on spray foam versus fiberglass batts and spray foam versus blown-in insulation.
Inspection and verification: Quality Insulation Installation
Meeting an R-value on paper is only part of compliance. Quality Insulation Installation (QII) is a prescriptive measure in all climate zones for newly constructed buildings and additions over 700 square feet, except low-rise multifamily in Climate Zone 7. It requires field verification by a certified rater under reference appendix RA3.5.
For multifamily buildings of three habitable stories or less, QII is required under Table 170.2-A in Climate Zones 1 to 6 and 8 to 16. A HERS rater verifies it and also checks the air barrier.
Practically, that means:
- The installer must leave the insulation visible and accessible before drywall or covering goes up.
- The rater inspects for gaps, compression, voids and continuous contact with the air barrier.
- The rater’s results go into the compliance documents your building department reviews.
Schedule insulation so the rater can inspect before walls close. Missing that window can mean opening finished assemblies later.
If you are pairing an insulation upgrade with new mechanical equipment, it is also worth keeping an eye on the heat pump tax credit changes, because a tighter envelope often changes how you size the HVAC system.
A practical path to compliance
- Confirm your permit date and scope. New build, addition or alteration? That sets which sections apply.
- Identify your climate zone. Your zone sets the R-30 or R-38 target and other requirements.
- Choose your path. Prescriptive is simplest. Performance gives flexibility if you want to trade insulation against other features.
- Check local amendments. Your building department can be stricter than the state.
- Pick a product that fits the assembly. Check framing depth, the R-value you need and whether the product is certified for California.
- Plan verification. If QII or SPF verification applies, schedule the rater before cover-up.
- Keep documents. Product certification, installer records and rater results go into the permit file.
Perspective
On code projects, we see the same pattern: the insulation is rarely the hard part, the details are. Gaps at penetrations, compressed batts in tight cavities and missed air sealing cost owners more than the material does.
That is why we recommend spray foam where the assembly is shallow or leaky. Closed-cell foam reaches higher R-values per inch and seals as it insulates, so one crew covers insulation and air sealing together. Our crews are certified and licensed in California, and we build to California energy and building code standards.
We also tell customers when a less expensive option will do. If a standard attic with room for depth can meet its target with fiberglass or blow-in, we say so and quote that. Our pricing is transparent, with no upselling, so you pay for what the code and your building need.
USA
What it costs: our published ranges
Prices depend on the assembly, access and the R-value you need. These are our published ranges:
| Service | Published range |
|---|---|
| Spray foam insulation | $1.00–$2.50 per board foot |
| Closed-cell insulation | $1.50–$2.50 per board foot |
| Fiberglass insulation | $0.50–$2.50 per sq ft |
| Blow-in insulation | $1.20–$3.50 per sq ft |
| Insulation removal | $1–$2 per sq ft |
A board foot is one square foot at one inch thick, so a 3-inch layer over 100 square feet is 300 board feet. A written quote for your project gives the exact figure.
Get your insulation job code-ready
We insulate and waterproof homes and commercial buildings across the San Francisco Bay Area, handling the whole building envelope with in-house crews. Every job is built to California energy and building code standards and comes with a workmanship warranty. Whether your project needs spray foam, fiberglass, blow-in, roofing or removal of old insulation, we recommend the option that meets your target without extras.
Tell us your address, scope and permit status, and we will quote it. See our spray foam insulation services or visit USA Spray Me to request an estimate. For commercial buildings, start with our commercial insulation page. Roof projects can start with our spray foam roofing system, and our guide on whether foam roofing complies with California building codes explains the code side.
FAQ
What is the Title 24 insulation requirement for a California attic?
For new single-family homes, the prescriptive requirement is R-38 in Climate Zones 1 and 11 to 16 and R-30 in Climate Zones 2 to 10, for insulation between wood framing members. Additions of 700 square feet or less have their own zone-based targets. Your climate zone and building department confirm the final number.
Does Title 24 apply if I only replace insulation?
The Energy Code covers additions and alterations, but not repairs. Whether replacement counts as an alteration of the envelope depends on scope, so ask your local building department before you start. We can help you describe the scope for a permit.
Is spray foam allowed under California’s energy code?
Yes. Spray polyurethane foam must be certified by the Bureau of Household Goods and Services, and it must meet fire code flame spread and smoke density limits. Compliance calculations use 3.6 R per inch for open-cell and 5.8 R per inch for closed-cell unless the product is listed for higher.
Do I need an inspector to verify my insulation?
Often, yes. Quality Insulation Installation requires verification by a certified rater for newly constructed buildings and additions over 700 square feet, with a Climate Zone 7 exception for low-rise multifamily. A rater must also verify spray foam when you claim R-values above the defaults.
Can my city require more than the state code?
Yes. Cities can amend the state code to be more restrictive when they make findings about local climatic, geologic or topographic conditions. Check with your local building department before finalizing plans.
Sources
- 2025 Building Energy Efficiency Standards program page, California Energy Commission
- City of Mountain View Council Report on the 2025 State Code
- Initial Statement of Reasons, 2025 Building Energy Efficiency Standards
- 2025 Reference Appendices, California Energy Commission
- Restructured 2025 Energy Code, Title 24 Part 6
- CEC-400-2025-005 Chapter 1
- Energy Efficiency Standards for Additions and Alterations, UpCodes
- 2025 Building Energy Efficiency Standards publication, California Energy Commission
- Performance and Prescriptive Compliance Approaches, UpCodes
- 2025 Nonresidential Compliance Manual, CEC-400-2025-008
- Section 170.2 Prescriptive Approach, 2025 California Energy Code
- 2022 Energy Code Multifamily Envelope, California Energy Commission
- 2022 Energy Code Fact Sheet: Single-Family Envelope
- Energy Code Ace, Section 110.8
- Energy Code Ace, Appendix RA2 Residential Verification
- Heat Pump Tax Credit 2026: What Changed and What’s Next
Recommended
- Air Sealing & Insulation to Pass Title 24 in 2025–2026 – A Practical Guide
- San Jose Building Code: New Home Insulation Requirements & Best Options
- San Francisco Building Code: New Home Insulation Requirements & Best Options
- Berkeley Building Code: New Home Insulation Requirements & Best Options
Get an Instant Quote From a Licensed California Insulation Contractor
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