The Cool-Roof Rule You Meet Only When You Re-Roof

It is the cool-roof rule, and its most counter-intuitive feature is this: it applies in more climate zones to a replacement roof than it does to a new house. A home built in 1968 in a zone where cool roofs were never required at construction can be held to the standard the day its roof is replaced.

This page sets out exactly where it applies, what it requires, who is exempt, and the several compliant ways out — including the ones that let you keep a dark roof.

So a spot repair or a partial replacement below that threshold does not pull the requirement in. A full tear-off, a full overlay, or any replacement covering more than half the roof does.

(For nonresidential and multifamily buildings the equivalent trigger is more than 50 percent of the roof area or more than 2,000 square feet, whichever is less — §141.0(b)2B and §180.2(b)1A. The 2,000 square-foot half of that test does not appear in the single-family section.)

Read the climate-zone columns against each other. New construction on a pitched roof triggers in zones 10–15. A re-roof on the same pitched roof triggers in zones 4 and 8–15 — a wider net. For low-slope roofs the gap is wider still: two zones for new construction, ten for a re-roof.

The values themselves are aged values. That is a deliberate choice in the code: reflectance is measured after three years of field exposure by the Cool Roof Rating Council, or computed from the initial value using the CRRC's aged-value protocol, because real roofs collect dirt and lose reflectance. Products must be CRRC-rated and labeled, and the 2025 cycle moved SRI calculation onto ASTM E1980 (2019).

The prescriptive values for single-family did not change between the 2022 and 2025 code cycles — but the 2025 code took effect 1 January 2026, so a project permitted now is working from the current edition.

So we used the California Energy Commission's own file — Building Climate Zones by ZIP Code, 2,694 ZIPs — and joined it against our own project records. Of 365 completed installations with the roof covering recorded, 320 carried a ZIP we could match to a climate zone.

Where our work sits:

And what that means at re-roof time:

Of the records matched to a Title 24 climate zone, 260 of 284 steep-slope roofs and 36 of 36 low-slope roofs are located in zones where cool-roof requirements can apply when more than 50 percent of the roof is replaced. Project-specific exceptions and the performance-compliance path may still apply.

Read that carefully, because it is a statement about geography, not obligation. It says nine out of ten pitched roofs we have worked on sit in a zone where this rule is live — not that every one of them must carry a reflective covering. Whether it actually binds a given project depends on how much of the roof is being replaced, which of the four alternatives the building already satisfies, whether the assembly clears the weight exemption, and whether the design is being shown compliant through the performance path rather than the prescriptive one.

The exceptions are geographic and specific: the coastal CZ 6 strip — parts of Los Angeles nearer the ocean, Camarillo, part of Thousand Oaks, part of Long Beach — and mountain CZ 16, which takes in the higher parts of Santa Clarita.

Note the asymmetry there, because it catches people out. In coastal CZ 6, a steep-slope roof is outside the re-roof requirement while a low-slope roof on the same street is inside it. Zone 6 appears in the low-slope list (4, 6–15) and not in the steep-slope list (4, 8–15).

A caution about cities. A city is not a climate zone. Los Angeles spans zones 9, 8 and 6 in our own records; Santa Clarita spans 9 and 16; Long Beach spans 8 and 6. This has to be resolved by ZIP or address, not by city name — which is precisely why the CEC publishes a ZIP file and an address lookup tool.

Roof constructions with a weight of at least 25 lb/ft² are exempt from the minimum requirements for aged solar reflectance and thermal emittance, or SRI.

That exemption appears against every one of the four rows in the table above — new construction and re-roof, steep and low.

It is stated as a weight threshold applying to the assembly, not as a material category. This distinction is not academic. It is common to read that "tile roofs are exempt," and that is not what the code says. Many tile assemblies do not reach 25 lb/ft²: the state's own Solar Permitting Guidebook assumes a tile roof assembly at 20 psf for structural screening purposes — below the exemption threshold. Lightweight concrete tile and a number of clay profiles fall short of 25; heavier profiles over solid sheathing can exceed it.

The honest instruction to a homeowner is therefore: the exemption exists, it is a number, and it applies to your specific assembly — have that weight established rather than assumed. A roofing contractor can give it from the product data and the deck build-up.

• a. a ceiling assembly with a U-factor of 0.025 or lower, or insulated with at least R-38 ceiling insulation;
• b. a radiant barrier in the attic — not installed directly above spaced sheathing, and meeting §150.1(c)2;
• c. in Climate Zones 2, 4, 9, 10, 12 and 14 — buildings that have no ducts in the attic;
• d. R-2 or greater continuous insulation above or below the roof deck.

The third one deserves more attention than it gets, because of where it applies. Climate Zone 9 covers most of the Los Angeles basin and San Fernando Valley — 76 percent of our own matched roofs sit in it. For a house in that zone with no HVAC ducts running through the attic, the cool-roof requirement is satisfied as the building already stands: no reflective product, no added insulation, no radiant barrier. Ducted attics are common in Los Angeles, so this will not apply to every house — but it is worth checking before assuming a light-colored roof is compulsory, and it is absent from most consumer guidance on this subject.

Note the limit of it, though. The duct alternative exists only in Climate Zones 2, 4, 9, 10, 12 and 14. A house in CZ 8 — which includes parts of Los Angeles, Long Beach and Lakewood — is subject to the requirement with no duct route available, and must use insulation, a radiant barrier or a compliant covering. The same is true in zones 11, 13 and 15.

The others are worth knowing too. If the attic is going to be insulated anyway — a common companion project to solar and electrification — the cool-roof requirement may already be satisfied by that work.

For low-slope re-roofs, the aged solar reflectance may alternatively be met using insulation at the roof deck per Table 150.2-B.

A note on partial work. Because the trigger is more than 50 percent of the roof being replaced, the scope of the job matters as much as the climate zone. Replacing one slope of a multi-plane roof, or repairing storm damage over part of the surface, may fall below the threshold. Where a project sits close to the line, the building department applying §150.2(b)1I is the authority on how the area is measured — ask before assuming either way.

There is one more exemption worth knowing, and it is solar-specific: building-integrated photovoltaic and building-integrated solar thermal panels are exempt, and on a re-roof the roof area covered by BIPV is not required to meet the reflectance minimums.

Note the limit of that. BIPV means the photovoltaic product is the roof covering — solar shingles and integrated panels, which the California Residential Code addresses separately in R905.15 and R905.16. A conventional rack-mounted array is not a roof covering; it sits above one. Rack-mounted panels do not exempt the roof beneath them.

Concrete and clay tile are extraordinarily durable — the covering can outlive the building's mortgage. The underlayment beneath it cannot. Felt underlayment is generally credited with something like 10 to 20 years of service under a covering; synthetic underlayments with roughly 20 to 35; rubberised asphalt with about 25 to 35. Those are industry and manufacturer ranges, not code figures, and they vary with ventilation and heat exposure — but the pattern holds regardless of the exact numbers: the tile is not what fails.

The code anticipates this. California Residential Code 2025, R908.5 provides that existing slate, clay or cement tile may be reinstalled — excluding any damaged, cracked or broken pieces, and requiring that rusted or deteriorated flashings, edgings, outlets and vents be replaced.

That single sentence is the legal basis for a lift-and-relay: the tile comes off, the underlayment beneath it is renewed, and the same tile goes back down. The roof is functionally new; the covering is the original.

Which sets up the sequencing problem. If a tile roof's underlayment is approaching the end of its life, that work is coming — and doing it after an array is installed means removing and reinstalling the array as well. This is the conversation to have before panels go on, not after, and it is a different conversation from the one about shingle wear, because the visible surface tells you almost nothing about the condition of what is underneath.

1. Cool-roof compliance — reflective covering, or one of the insulation alternatives, or a documented ≥25 lb/ft² assembly.
2. Underlayment specification — which product, and what service life it buys relative to the array's 25 years.
3. Array layout — decided against a roof that is about to change.

Taken together, these are resolved once. Taken separately, at least one of them is revisited at cost — usually the array, which has to come off so the layer underneath it can be dealt with.

• California Residential Code 2025 (Title 24, Part 2.5), R908.5 — reinstallation of existing slate, clay or cement tile, excluding damaged pieces.
• California Residential Code 2025, R905.15, R905.16 — BIPV shingles and BIPV roof panels as roof coverings.
• Underlayment service-life figures are industry and manufacturer ranges, not code or standards values.

Figures on this page come from the primary sources below and, where noted, from Cali Energy calculations using the stated assumptions. Rates, incentives, and program terms change; each was verified September 1, 2026.

1. California Energy Code (Title 24, Part 6) 2025 — §150.1(c)11A and B (new construction, steep and low slope) and §150.2(b)1Ii and 1Iii(a)…
2. Cool Roof Rating Council — California Title 24 overview and Rated Products Directory
3. California Energy Commission — Building Climate Zones by ZIP Code (2,694 ZIPs)
4. California Energy Commission — Climate Zone tool and maps
5. California Solar Permitting Guidebook, 4th Edition, Part 3 — tile roof assembly assumed at 20 psf for structural screening
6. California Building Standards Commission — 2025 Title 24 effective 1 January 2026