Research study

Does an ADU have to have solar?

Name: California ADU solar mandate applicability: Energy Code classification, prescriptive PV sizing by climate zone, and the 1.8 kWdc exemption threshold
Creator: HyreADU Research Desk
Published: 2026-09-05
License: https://creativecommons.org/licenses/by/4.0/

Two tests, applied in order. Most ADUs fail the first one and never reach the second — and a surprising number of the ones that do reach it are exempt anyway, by arithmetic.

Updated September 2026 · Data as of California Energy Commission 2022 Single-Family Residential Compliance Manual (CEC-400-2022-006, May 2022), chapters 7 and 9, retrieved as PDF and text-extracted 2026-09-05; Government Code § 66323 retrieved from leginfo.legislature.ca.gov 2026-09-05; code edition dates from the California Building Standards Commission 2026-09-05

Written by HyreADU Research Desk Primary-source research and data analysis

Audited by HyreADU Research Desk Code citation and calculation audit

7 of 16 climate zones where an 800 sq ft new detached ADU falls under the threshold HyreADU calculation applying CEC Equation 7-1 with the Table 7-1 factors at CFA 800, one dwelling unit, against the 1.8 kWdc floor in Exception 2. CEC 2022 Single-Family Residential Compliance Manual, ch. 7. Retrieved 2026-09-05.

Addition is what the Energy Code calls most ADUs — and additions are outside the mandate CEC 2022 Single-Family Residential Compliance Manual §9.3.5 and Figure 9-2. Only a detached newly built unit, or one joined by a breezeway or covered walkway, is a newly constructed building.

80 sq ft of contiguous qualifying roof — below it, Exception 1 removes the requirement “No PV system is required if the SARA is less than 80 contiguous square.” Solar Access Roof Area excludes “any roof area with less than 70 percent annual solar access.” CEC manual §7.2.2.

The finding

Test one: is the ADU a “newly constructed building” under the Energy Code, or an “addition”? The prescriptive photovoltaic requirement at Energy Code section 150.1(c)14 applies to newly constructed single-family buildings, and the California Energy Commission publishes a mechanical classification test for ADUs.

A detached, newly built unit is a newly constructed building; so is one “attached to existing home by breezeway, or covered walkway”.

Everything else — converted existing space, a newly built unit attached to the house, a unit on or beside an existing detached garage — is an addition.

Additions are outside the prescriptive PV mandate, so a garage conversion, a basement conversion, a JADU and a bump-out are not caught by it at all.

Test two, for the units that are newly constructed buildings: run the equation, and check Exception 2. The CEC’s Equation 7-1 sizes the required system as kW_PV = (CFA × A)/1000 + (N_Dwell × B), where A and B are climate-zone factors published in Table 7-1.

Exception 2 is one sentence: “No PV system is required when the minimum PV system is less than 1.8 kWdc.” HyreADU calculation: run that equation at 800 square feet — the by-right detached ceiling in Government Code section 66323(a)(2) — for one dwelling unit, and the result falls below 1.8 kWdc in 7 of California’s 16 climate zones: zones 2, 3, 4, 5, 6, 7 and 16.

It is above the threshold in the nine hotter and sunnier zones. Four further exceptions can also remove the requirement, one of them on roof area rather than climate. Everything quoted is from the 2022 Energy Code. Not engineering, legal or financial advice.

Read this first

Code applicability is the question here, not whether solar is a good buy
The question here is narrow: what does Title 24, Part 6 require of this unit, and what triggers an exception.
We do not price panels, compare inverters, model bill savings, or express a view on whether solar on an ADU is a good investment.
Those are different questions with different evidence and they are not answered on this page.
Everything quoted is from the 2022 Energy Code
The California Energy Commission states that “[b]uildings whose permit applications are applied for on or after January 1, 2026, must comply with the 2025 Energy Code,” and the Building Standards Commission confirms the 2025 Title 24 was published 1 July 2025 with an effective date of 1 January 2026.
We could not retrieve the 2025 compliance manual. If your permit application is dated on or after 1 January 2026, treat every figure here as a starting point to be re-checked, not as an answer.
The climate-zone table is a calculation, not an observation
The A and B factors are the Commission’s, quoted exactly. The resulting kilowatt figures and break-even floor areas are HyreADU arithmetic applying the Commission’s published equation.
They are reproducible from the table on this page in a spreadsheet, and we would rather you checked them than took them. They are not a compliance determination for any building.
Only a licensed professional using CEC-approved software produces a compliance document
Prescriptive compliance is documented on the certificate of compliance a designer or an energy consultant prepares, and the Commission requires shading to be documented “by using the CEC-approved solar assessment tool”. A page cannot certify a building, and the arithmetic here is not a substitute for that process.

Why this question has three confident wrong answers in circulation

The 2019 Energy Code was widely reported as “California requires solar on all new homes”. That reporting was roughly right about houses and wrong about almost everything else, and it has been copied forward for seven years. An ADU is not a house, and the Energy Code does not treat it as one by default.

The three answers you will find are: yes, all ADUs need solar; no, ADUs are exempt; and only detached ADUs need solar. The third is the closest and is still incomplete, because it stops at test one.

A detached, newly built ADU is inside the mandate — and can then be exempted anyway by Exception 1 on roof area, by Exception 2 on system size, or by Exception 3, 4 or 5.

HyreADU analysis: the reason the second test is missing from the public conversation is arithmetic rather than law.

Exception 2 is a fixed floor of 1.8 kWdc, and Equation 7-1 carries a per-dwelling-unit constant — the B factor — that is between 1.06 and 1.51 kW before a single square foot of floor area is counted.

On a house of 2,000 square feet the floor area term dominates and the exception is irrelevant.

On an ADU of 800 square feet the constant dominates, and whether the total clears 1.8 comes down to which climate zone the lot sits in. Nobody ran it because nobody had reason to run it at ADU scale.

Test one: is your ADU a newly constructed building?

The Energy Commission publishes this test for ADUs specifically. It is not a matter of judgment, and it decides whether the prescriptive PV requirement is in play at all.

The ADU	Energy Code classification	Prescriptive PV requirement in play?	CEC wording
Detached, newly constructed structure	Newly constructed building	Yes — go to test two	“If the ADU shares no common walls with the existing dwelling unit (detached) and is a new structure, this is a newly constructed residential building.”
Newly constructed, joined to the house by a breezeway or covered walkway	Newly constructed building	Yes — go to test two	“Newly Constructed Building: Newly constructed ADU attached to existing home by breezeway, or covered walkway.”
Conversion of existing unconditioned space, detached (detached garage, workshop)	Addition	No	“Addition: Converting existing unconditioned space, detached from existing home. Walls may qualify as ‘existing wall with siding.’”
Conversion of existing unconditioned space, attached (attached garage)	Addition	No	“Addition: Converting existing unconditioned space, attached to existing home.”
Newly constructed and attached to the existing home	Addition	No	“Addition: Newly constructed, attached to existing home. One or more walls may qualify as wall extensions.”
Newly constructed above or beside an existing detached garage	Addition	No	“Addtion: Newly constructed ADU on top of existing detached garage or side-by-side with existing detached garage.” (Typographical error in the source retained.)
Junior ADU inside the single-family residence	Addition	No	A JADU is “no more than 500 square feet in size and contained entirely within an existing single-family building.”

Quoted from section 9.3.5 and Figure 9-2 of the California Energy Commission’s 2022 Single-Family Residential Compliance Manual (CEC-400-2022-006, May 2022), retrieved and text-extracted 2026-09-05. The classification wording is the Commission’s; the middle column is the desk applying it.

The Commission attaches its own warning to this table, and it is worth carrying: “Although the Energy Code that applies to the ADU may be the same as an addition, this may not be the same for other Parts of Title 24. Check with your local building department to confirm applicable requirements.” An Energy Code classification does not travel to the Building, Residential, Electrical or Plumbing Codes.

Test two: run the equation, then check the 1.8 kW floor

Equation 7-1: kW_PV = (CFA × A)/1000 + (N_Dwell × B). The A and B columns are quoted from the Commission’s Table 7-1. The last three columns are HyreADU arithmetic at CFA = 800 square feet and one dwelling unit — the by-right detached size in Government Code section 66323(a)(2).

Required PV system size for an 800 sq ft, one-dwelling-unit, newly constructed ADU, by California climate zone, against the 1.8 kWdc floor in Exception 2. Gold columns fall below the floor and carry no PV requirement. The pattern is not a coastal-inland gradient in the way you would expect from sunshine — it is driven mainly by the per-dwelling constant B, which is a modeled load term rather than a solar-resource term. Chart: HyreADU Research Desk. HyreADU calculation applying CEC Equation 7-1 with the Table 7-1 climate-zone factors quoted in the table below. Formula, factors and threshold are the California Energy Commission’s; the arithmetic is ours and is reproducible from this page.

Climate zone	Representative places	A (CFA factor)	B (dwelling factor)	kWdc at 800 sq ft	Below 1.8 kW floor?	Floor area at which the requirement starts
CZ 1	North coast (Eureka, Arcata)	0.793	1.27	1.90	No — PV required	668 sq ft
CZ 2	Santa Rosa, Napa	0.621	1.22	1.72	Yes — no PV required	934 sq ft
CZ 3	San Francisco, Oakland	0.628	1.12	1.62	Yes — no PV required	1,083 sq ft
CZ 4	San José, Santa Cruz	0.586	1.21	1.68	Yes — no PV required	1,007 sq ft
CZ 5	Santa Maria, coastal central	0.585	1.06	1.53	Yes — no PV required	1,265 sq ft
CZ 6	Los Angeles coastal, Torrance	0.594	1.23	1.71	Yes — no PV required	960 sq ft
CZ 7	San Diego coastal	0.572	1.15	1.61	Yes — no PV required	1,136 sq ft
CZ 8	Los Angeles inland (El Toro)	0.586	1.37	1.84	No — PV required	734 sq ft
CZ 9	Los Angeles basin (Pasadena)	0.613	1.36	1.85	No — PV required	718 sq ft
CZ 10	Riverside, San Bernardino	0.627	1.41	1.91	No — PV required	622 sq ft
CZ 11	Red Bluff, northern valley	0.836	1.44	2.11	No — PV required	431 sq ft
CZ 12	Sacramento, Stockton	0.613	1.40	1.89	No — PV required	653 sq ft
CZ 13	Fresno, Bakersfield	0.894	1.51	2.23	No — PV required	324 sq ft
CZ 14	Palmdale, high desert	0.741	1.26	1.85	No — PV required	729 sq ft
CZ 15	Palm Springs, low desert	1.560	1.47	2.72	No — PV required	212 sq ft
CZ 16	Mountain (Blue Canyon, Tahoe)	0.590	1.22	1.69	Yes — no PV required	983 sq ft

Columns A and B are quoted verbatim from Table 7-1, “CFA and Dwelling Adjustment Factors”, in the CEC 2022 Single-Family Residential Compliance Manual, chapter 7, retrieved 2026-09-05.

Columns five to seven are HyreADU calculations from Equation 7-1 in the same chapter, at CFA 800 sq ft and one dwelling unit, against the Exception 2 floor of 1.8 kWdc.

Representative places are the desk’s plain-language gloss and are illustrative — confirm your parcel’s climate zone with your building department, not from this column.

Read the last column carefully, because it is the useful one. It is the conditioned floor area at which the prescriptive PV requirement switches on for a one-unit newly constructed building in that zone.

In climate zone 15 it is 212 square feet — effectively every ADU.

In climate zone 5 it is 1,265 square feet, which is above the 1,200 square foot detached ceiling in Government Code section 66314, meaning no detached ADU in that zone reaches the threshold on floor area alone.

That is a real and, as far as we can find, unpublished consequence of two independent code provisions meeting.

The five exceptions, in the Commission’s own words

All five are quoted from section 7.2.2 of the compliance manual. The Commission notes they “can also be used under the performance approach”, where the user “must select the appropriate exception”.

Exception 1 — not enough qualifying roof

“[M]ay apply if there is limited unshaded roof space. For steep slope roofs, SARA shall not consider roof areas with a northerly azimuth that lies between 300 degrees and 90 degrees from true north. No PV system is required if the SARA is less than 80 contiguous square.”

SARA is Solar Access Roof Area: “[t]he area of the building’s roof, covered parking areas, carports, and all other newly constructed structures that are capable of structurally supporting a PV system … SARA does not include any roof area with less than 70 percent annual solar access.” HyreADU note: a small detached ADU in a mature-tree neighborhood, or one deliberately sited in the shade of the house, can land here.

The Commission requires shading to be documented with its approved solar assessment tool, not asserted.

Exception 2 — the system would be smaller than 1.8 kW

“No PV system is required when the minimum PV system is less than 1.8 kWdc.”

One sentence, no conditions, and the one that does most of the work at ADU scale. See the table above for where an 800-square-foot unit lands.

Exception 3 — snow load

“Buildings with enforcement-authority-approved roof designs, where the enforcement authority determines it isn’t possible for the PV system, including panels, modules, components, supports, and attachments to the roof structure, to meet the snow load requirements of Ch. 7 in the American Society of Civil Engineers (ASCE) Standard 7-16.”

A determination by the enforcement authority, not by the owner or the designer. Relevant in climate zone 16 and parts of zone 1.

Exception 4 — pre-2020 planning conditions

“For buildings that are approved by the local planning department prior to January 1, 2020 with mandatory conditions for approval: 1. Shading from roof designs and configurations for steep-sloped roofs, which are required by the mandatory conditions for approval, shall be considered for the annual solar access calculation. 2. Roof areas, that are not allowed by the mandatory conditions for approval to have PVs, shall not be considered in determining the SARA.”

This is the design-review carve-out — the historic district or design-guideline case where the roof form or the ban on street-facing panels was imposed by the planning department. Note the hard date: approval before 1 January 2020.

Exception 5 — battery storage buys a 25 per cent reduction

“[M]ay apply to buildings with a battery storage system. PV system sizes determined using equation 150.1-C may be reduced by 25 percent if installed in conjunction with a battery storage system. The battery storage system shall meet the qualification requirements specified in Join[t] Appendix JA12 and have a minimum usable capacity of 7.5 kWh.”

HyreADU note: this is a reduction, not an exemption — but a 25 per cent reduction can push a marginal ADU under the 1.8 kW floor and thereby into Exception 2. Whether trading a required array for a required battery is sensible is an economic question this page does not answer.

And what remains when an exception applies: solar ready

Exempt is not the same as unaffected. The manual is explicit: “[t]he requirements for solar ready buildings are mandatory measures for newly constructed single-family residential buildings that do not have a PV system due to an exception in Section 150.1(c)14.” The intent is “to reserve a penetration-free and shade-free portion of the roof for the potential future installation of a solar energy system,” and “[t]here are no requirements to install panels, conduit, piping, or mounting hardware.”

So an exempted new detached ADU still has to keep a piece of its roof clear. That constrains where the vents, the flue and the skylights go, and it is a drawing-stage decision.

How to work out your own answer

Five steps, in order. The first two are free and settle most cases.

1
Classify the unit against the CEC’s own list
Detached and newly built, or joined only by a breezeway or covered walkway — newly constructed building. Anything else on the Commission’s list — an addition. If it is an addition, the prescriptive PV mandate is not in play and you can stop here. Most ADUs stop here.
2
Find your parcel’s climate zone from the building department, not from a map on a blog
Climate zone assignment is by location and is administered locally. It is the single input that most changes the answer, and getting it from a secondary source is how people end up designing to the wrong zone. Ask the counter, and write down what they say.
3
Run Equation 7-1 with the published factors, then test it against 1.8 kW
kW = (conditioned floor area × A) ÷ 1000 + (1 × B). The A and B values for your zone are in the table above, quoted from the Commission. If the result is below 1.8, Exception 2 is available. This is arithmetic you can and should check — it takes a spreadsheet a second.
4
Have the roof assessed before you rely on Exception 1
The 80-square-foot SARA test depends on annual solar access below 70 per cent, which is a shading calculation, not an eyeball judgment. The Commission requires it to be documented with its approved solar assessment tool. That is a designer’s or energy consultant’s task.
5
Have a designer or energy consultant produce the certificate of compliance either way
The prescriptive path is documented on a certificate of compliance submitted with the permit application, and the performance path requires CEC-approved modeling software. Nothing on this page is that document. If an exception applies, the solar-ready mandatory measures still have to be shown on the drawings.

What this page deliberately does not say

Nothing here says whether you should install solar on your ADU. Code compliance and financial sense are different questions, and conflating them is how a research page turns into a sales page.

If the code requires a system, the question of whether to install one does not arise; if it does not, the question is an economic one that depends on your tariff, your consumption, your roof and your capital cost — none of which this page knows.

It also makes no claim about rooftop solar economics under any particular net-metering or net-billing regime, because that is not an ADU question and we have not researched it here.

Where the exemption is most likely to surprise someone: a builder who assumed a mandate that does not apply, and specified a system into the budget for an addition-class ADU in a coastal climate zone.

That is an avoidable cost, and it is avoidable at drawing stage for the price of reading two paragraphs of the Commission’s manual.

What we could not verify

The 2025 Energy Code’s photovoltaic provisions and its ADU classification. This is the most important gap on the page. The 2025 standards apply to permit applications submitted on or after 1 January 2026.

We retrieved the Commission’s page confirming that date and the Building Standards Commission’s confirmation that the 2025 Title 24 was published 1 July 2025, but we could not retrieve the 2025 single-family compliance manual.

Every equation, factor, exception and classification quoted here is from the 2022 manual, dated May 2022. Re-check before relying on any of it for a 2026 application.

The regulatory text of section 150.1(c)14 itself. We worked from the Commission’s compliance manual, which is the Commission’s own explanation of its own standard and quotes the exceptions in terms. We did not open Title 24, Part 6 directly. Where the manual and the regulation could differ, the regulation governs.

Climate zone assignment by jurisdiction. The “representative places” column is a plain-language gloss by this desk and is not authoritative. We did not retrieve the Commission’s climate zone boundary dataset for this edition, and a parcel can sit in a different zone from the city it is nominally in.

Any local reach code that goes further. A jurisdiction may adopt locally amended energy standards more stringent than Title 24 under Public Resources Code section 25402.1(h)(2). Nothing on this page reflects local amendments. See our reach-code study for that layer and for the limits of what we could retrieve about it.

Questions

Do ADUs need solar panels in California?

Only some of them, and the test runs in two stages. First, the prescriptive photovoltaic requirement in Energy Code section 150.1(c)14 applies to newly constructed buildings, and the California Energy Commission classifies most ADUs as additions rather than newly constructed buildings — every conversion of existing space, every newly built unit attached to the house, and every unit built on or beside an existing detached garage. Only a detached, newly built unit, or one joined to the house solely by a breezeway or covered walkway, is a newly constructed building. Second, even those can be exempted by one of five exceptions.

Does a garage conversion ADU need solar?

No, not under the prescriptive photovoltaic requirement. The Commission classifies “[c]onverting existing unconditioned space” — attached or detached — as an addition, and the prescriptive PV requirement applies to newly constructed buildings. That said, the conversion still has to comply with the Energy Code provisions that do apply to additions, and this page does not enumerate those. Have a designer or energy consultant confirm the compliance path.

What is the 1.8 kW exception?

Exception 2 to the prescriptive photovoltaic requirement, quoted in full by the Commission as: “No PV system is required when the minimum PV system is less than 1.8 kWdc.” Because the sizing equation carries a fixed per-dwelling-unit term of between 1.06 and 1.51 kilowatts depending on climate zone, plus a small floor-area term, a compact ADU can compute out below that floor. HyreADU calculation: at 800 square feet with one dwelling unit, seven of the sixteen climate zones fall below it — zones 2, 3, 4, 5, 6, 7 and 16.

How big a solar system would my ADU need if it does apply?

The Commission’s Equation 7-1 is kWPV = (conditioned floor area × A) ÷ 1000 + (number of dwelling units × B), with A and B taken from Table 7-1 for the building’s climate zone. Both columns are reproduced on this page. At 800 square feet and one dwelling unit the result runs from 1.53 kWdc in climate zone 5 to 2.72 kWdc in climate zone 15. This is arithmetic from a published formula and is not a compliance determination — the certificate of compliance is prepared by a designer or energy consultant using approved software.

If my ADU is exempt, is there anything else I have to do?

Yes. The compliance manual is explicit that the solar-ready requirements “are mandatory measures for newly constructed single-family residential buildings that do not have a PV system due to an exception in Section 150.1(c)14.” The intent is “to reserve a penetration-free and shade-free portion of the roof for the potential future installation of a solar energy system,” and the Commission notes “[t]here are no requirements to install panels, conduit, piping, or mounting hardware.” It constrains roof penetrations, so it is a drawing-stage matter.

Can a battery get me out of the solar requirement?

Not out of it, but down. Exception 5 provides that PV system sizes “may be reduced by 25 percent if installed in conjunction with a battery storage system,” where the battery “shall meet the qualification requirements specified in Join[t] Appendix JA12 and have a minimum usable capacity of 7.5 kWh.” A 25 per cent reduction can push a marginal computation below the 1.8 kWdc floor and into Exception 2. Whether that trade is worth making financially is not a question this page answers.

What if my roof is shaded?

Exception 1 may apply. Solar Access Roof Area excludes “any roof area with less than 70 percent annual solar access”, and on steep-slope roofs it disregards roof areas “with a northerly azimuth that lies between 300 degrees and 90 degrees from true north”. If the qualifying area is “less than 80 contiguous square” feet, no PV system is required. The Commission requires shading to be documented using its approved solar assessment tool rather than asserted, so this is a designer’s determination.

Which Energy Code edition applies to my project?

It is set by the date of the permit application. The California Energy Commission states that “[b]uildings whose permit applications are applied for on or after January 1, 2026, must comply with the 2025 Energy Code.” The Building Standards Commission confirms the 2025 Title 24 was published on 1 July 2025 with an effective date of 1 January 2026, and that the 2022 edition took effect on 1 January 2023. Everything quoted on this page is from the 2022 edition, which is the one we were able to retrieve and read.

Written and audited by

HyreADU Research Desk

Primary-source research, data analysis and fact checking

We are a research desk, not a builder. We read the permit extract, the statute, the HCD return or the fee schedule ourselves, and publish each figure with its source and retrieval date.

Where a number cannot be traced to a primary source, we leave it out and say what we could not verify. Our store-based claims cover California only.

CA: the only state this desk will make store-based claims about
5: jurisdictions with extracted ADU permit evidence
735: CSLB-verified companies in the California store
0: national claims from a one-state store

How this desk works

Primary sources only. Permit counts come from the city or county that issued the permit. Production counts come from HCD’s Annual Progress Report. Rents come from HUD or the Census. We do not cite an article that cites a source; we download the source and compute the figure ourselves.
This is a California site. The company store is 734 California firms and one New Mexico firm. Permit evidence exists for five named jurisdictions: Los Angeles, San Francisco, Sacramento, San José and unincorporated Marin. A number from that store is titled to those places, never to the United States.
A permit is not a completion, and a license is not an ADU grade. California licenses no ADU classification. Being named on an ADU permit is evidence of engagement in that jurisdiction, not of quality, completion, or work anywhere else. Owner-builder permits are excluded from contractor counts.
Calculation is labeled as calculation. Figures we derive are never presented as something HCD, HUD, the Census or a city published. Terner Center research is cited as Terner’s, never restated as ours.
We do not design, permit or build ADUs, and we take no payment for placement, ranking or a favorable mention. Pages that look like rankings are not: they publish public-record counts and let the reader decide.
Nothing here is legal, tax or financial advice. Zoning, underwriting and appraisal practice vary by jurisdiction, lender and appraiser. The useful next step on a specific lot is the planning counter and a licensed professional.

Data as of California Energy Commission 2022 Single-Family Residential Compliance Manual (CEC-400-2022-006, May 2022), chapters 7 and 9, retrieved as PDF and text-extracted 2026-09-05; Government Code § 66323 retrieved from leginfo.legislature.ca.gov 2026-09-05; code edition dates from the California Building Standards Commission 2026-09-05. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold.

Our editorial policy sets out how we source, date and correct what we publish.

Sources & retrieval dates

California Energy Commission, 2022 Single-Family Residential Compliance Manual (CEC-400-2022-006), May 2022 — chapter 7 , Retrieved as PDF and text-extracted 2026-09-05. Equation 7-1 and Table 7-1 “CFA and Dwelling Adjustment Factors” for all sixteen climate zones; the SARA definition; the five exceptions quoted in full on this page; and the solar-ready mandatory measures for buildings exempted under an exception (“The requirements for solar ready buildings are mandatory measures for newly constructed single-family residential buildings that do not have a PV system due to an exception in Section 150.1(c)14”). Retrieved 2026-09-05.
California Energy Commission, 2022 Single-Family Residential Compliance Manual — section 9.3.5, “Accessory Dwelling Units (ADUs)” and Figure 9-2 , The classification test quoted in test one above: “For compliance, an ADU may be either an addition or a newly constructed building.” Figure 9-2 enumerates the six cases. Includes the Commission’s own caution that the Energy Code classification “may not be the same for other Parts of Title 24.” Retrieved 2026-09-05.
California Energy Commission — 2025 Building Energy Efficiency Standards , “Buildings whose permit applications are applied for on or after January 1, 2026, must comply with the 2025 Energy Code.” Establishes that everything quoted on this page from the 2022 manual has a defined expiry for new applications. Retrieved 2026-09-05.
California Energy Commission — 2022 Building Energy Efficiency Standards , The Commission’s standards page: the 2022 update “expands solar photovoltaic and battery storage standards”, and “[b]uilders must verify and document the shading conditions of a building’s installed solar photovoltaic (PV) system by using the CEC-approved solar assessment tool.” Retrieved 2026-09-05.
California Energy Commission, 2022 Building Energy Efficiency Standards Summary (fact sheet) , Retrieved as PDF and text-extracted 2026-09-05. Confirms the direction of travel this page depends on: the 2019 code “ventured into onsite generation by requiring solar PV on new homes”, and the 2022 update “[a]llows exceptions to existing solar PV standards when roof area is not available (such as for smaller homes).” Retrieved 2026-09-05.
California Building Standards Commission — code editions and effective dates , “The 2025 California Building Standards Code (Cal. Code Regs., Title 24) will be published July 1, 2025, with an effective date of January 1, 2026.” The 2022 edition “was published July 1, 2022, with an effective date of January 1, 2023.” Part 6 is the California Energy Code. Retrieved 2026-09-05.
California Government Code § 66323 — the by-right ADU categories , The source of the 800-square-foot figure this page runs the equation at: one detached new-construction ADU that does “not exceed four-foot side and rear yard setbacks” and is “not more than 800 square feet of livable space”. Retrieved 2026-09-05.
California Government Code § 66314 — maximum standards, including the detached size ceiling , “The total floor area for a detached accessory dwelling unit shall not exceed 1,200 square feet.” Used for the observation that in climate zone 5 the floor area at which the PV requirement switches on (1,265 sq ft by our calculation) sits above the statutory ceiling for a detached unit. Retrieved 2026-09-05.
California Public Resources Code § 25402.1 — local energy standards more stringent than Title 24 , The provision under which a jurisdiction may adopt a reach code, requiring that “the city or county files the basis of its determination that the standards are cost effective with the commission and the commission finds that the standards will require the diminution of energy consumption levels”. Cited because a local amendment can change everything on this page for a given lot. Retrieved 2026-09-05.

Two questions settle it, and both are free

Is the unit a newly constructed building or an addition, and which climate zone is the parcel in? Get the second from your building department in writing. The feasibility checker walks the questions that surface both, and it will never tell you that you can build.

Feasibility checker Electrical service study

HyreADU does not design, permit or build accessory dwelling units, and does not sell, install or finance solar equipment. This page is informational and is not engineering, legal or financial advice, and it is not a solar buying guide.

It describes what the California Energy Code required as retrieved on 5 September 2026, working from the California Energy Commission’s 2022 Single-Family Residential Compliance Manual; the 2025 Energy Code governs permit applications submitted on or after 1 January 2026 and its manual was not retrieved.

The climate-zone figures on this page are arithmetic applications of a published formula, labeled as calculations, and are not a compliance determination for any building.

A certificate of compliance is prepared by a designer or energy consultant using CEC-approved software, and shading must be documented with the Commission’s approved solar assessment tool. Confirm your parcel’s climate zone with your building department.