Building an ADU in Rolling Hills. Rules, costs, timeline.

Can I build an ADU in Rolling Hills?

Everything in this section comes from RHMC Chapter 17.28 (§§ 17.28.010 to 17.28.100), read together with the RA-S zone standards at §§ 17.16.060 to 17.16.130 and cross-checked against Gov. Code §§ 66310–66342 and the HCD ADU Handbook (March 2026).

Five things to know before you start

The five points a planner would raise first, before any regulation gets explained.

How many units a Rolling Hills lot can carry

The ordinance splits ADUs into two classes, and the distinction does real work. Class 1 units are the ones Gov. Code § 66323 requires every city to permit. Class 2 units are the ones Rolling Hills regulates locally under §§ 66314–66322 (§ 17.28.040(B)). Class 1 units are exempt from the local development standards in § 17.28.060 — the size ceilings, the 30-foot front setback, the floor-area and lot-coverage rules, the parking requirement and the architectural matching rules all belong to Class 2 and none of them reaches a Class 1 unit.

The ordinance says the combination out loud, which many do not: a unit approved under § 17.28.040(B)(1)(a) “may be combined with an ADU approved under subsection (B)(1)(b).” There is one hard exception to all of it. No ADU or junior ADU may be created on a parcel that resulted from a subdivision under Gov. Code § 66499.41 — the Starter Home Revitalization Act (§ 17.28.100). That is a choice the City has made rather than a rule the state imposed: § 66499.41(g) provides only that a local agency is not required to permit ADUs or junior ADUs on parcels created under that authority. And it is not the SB 9 rule — an SB 9 urban lot split is Gov. Code § 66411.7, which Rolling Hills regulates in a separate chapter, RHMC Chapter 17.45.

An existing nonconformity is not your problem

This matters more in Rolling Hills than in most places, because RA-S lots routinely carry a structure inside the zone’s generous setbacks, coverage above the 20% figure at § 17.16.070, or a guest house over 200 square feet built without the conditional use permit § 17.16.040(A)(3) requires. None of that has to be cured first. Section 17.28.020(D) provides that a conforming ADU or junior ADU is not required to correct a nonconforming zoning condition, and § 17.28.080(A) bars the City from denying the application over a nonconforming zoning condition, a building-code violation or an unpermitted structure that does not threaten public health and safety and is not affected by the ADU’s construction. Those track Gov. Code §§ 66322(b) and 66323(c). The City can still enforce applicable building standards under Health & Safety Code § 17980.12 — but it cannot hold your ADU hostage to an unrelated legacy condition.

Owner-occupancy

You do not have to live there. Section 17.28.050(G)(1) states that ADUs are not subject to an owner-occupancy requirement, which is what Gov. Code § 66315 requires. Junior ADUs are different, and Rolling Hills has already written the current rule into its code rather than carrying the older, broader version most cities still show: owner occupancy applies, except where the junior ADU has its own separate sanitation facilities, or where the property is entirely owned by a governmental agency, land trust or housing organization (§ 17.28.050(G)(2)). The separate-bathroom exception is AB 1154, effective January 1, 2026, amending Gov. Code § 66333(b).

What an ADU costs in Rolling Hills (2026)

Our Signature plans are fixed-price — architectural design and full permit processing included, the same number whether the lot is in Rolling Hills, Palos Verdes Estates or the Westside. Construction is separate: once your plans are permitted, you build it yourself, bring your own licensed contractor, or build with one of our vetted construction partners. The figures below are the estimated cost to build each model with an independent licensed general contractor.

Only the six single-story plans appear here. The three two-story Signature Homes are detached buildings of roughly 25 feet and cannot be permitted on a Rolling Hills lot as drawn — the detached cap is 16 feet, and the attached route that could carry two storeys is capped at the zone’s 21 feet — so quoting them on this page would be quoting something you cannot build.

What is fixed is the plan: our Signature plan fees run $7,490 to $12,990 — architectural design and full permit processing included. We can price it because the Signature Homes were engineered to pass objective ADU standards on paper, and the Rolling Hills standards are objective throughout Chapter 17.28. The build figures above are an estimate by an independent licensed general contractor: your plans, your choice of builder.

For sizing and payback math, try our ADU calculator and the ROI calculator.

Development fees, and the three costs Rolling Hills adds

Two square-foot thresholds do most of the work on fees, and both come from state law before they come from the ordinance. An ADU of 750 sqft or less and any junior ADU are exempt from impact fees entirely — defined at § 17.28.070(A)(1) as Mitigation Fee Act and Quimby Act fees, expressly excluding water and sewer connection fees and capacity charges. A unit under 500 sqft does not increase assessable space and so escapes school fees (§ 17.28.070(A)(2); Gov. Code § 66311.5(c)(3); Education Code § 17620). Above 750 square feet, § 17.28.070(A)(3) requires any impact fee to be prorated to the ADU’s share of the primary dwelling’s floor area — stated the right way round, which is not universal in Los Angeles County.

One rule cuts the other way and matters more than usual in a city with no sewer. For a junior ADU or a conversion ADU created under § 17.28.040(B)(1)(a), no new or separate utility connection may be required and no connection fee or capacity charge may be charged at all (§ 17.28.070(B)(2); Gov. Code § 66311.5(d)). The exceptions are narrow: a unit built together with a new single-family home, or one being separately conveyed where that is allowed. Every other ADU does need its own connection for any utility the City provides, at a fee proportionate to the burden it creates, measured by floor area or drainage-fixture units (§ 17.28.070(B)(3)).

The City may charge a processing fee for the ADU permit itself, set by the Director of Community Development and approved by City Council resolution (§ 17.28.040(A)(2)); the Planning Department publishes its own fee schedule. Building permit, plan-check and inspection fees are not the City’s at all — those run through Los Angeles County Building and Safety at its Lomita office, or through Willdan Associates, which the City offers as an alternative, and they are valuation-based. Your Backyard Review includes a line-item estimate of the pass-through costs for your specific lot.

Three Rolling Hills-specific costs sit outside all of that, and they are the ones that surprise people. The City’s published planning FAQ states that soils and geology reports are required for all projects, without carve-outs — this is the Palos Verdes Peninsula and the City runs an active land-movement monitoring program, so the report is substantive work rather than a formality. Utility lines serving a new accessory structure must be placed underground. And where the unit will connect to an onsite wastewater system, you need a current percolation test and, often, septic capacity work to go with it. Price all three before design, not after.

What it returns: renting your ADU

A Rolling Hills ADU is a long-term rental asset or it is family housing. Rentals shorter than 30 days are barred twice: by § 17.28.050(D), regardless of when the unit was created, and by § 17.16.020(B), which makes it unlawful to offer, rent or occupy any dwelling or room in a dwelling for compensation for less than 30 days anywhere in the RA-S zone. State law goes one day further still. Gov. Code § 66323(e) requires a term longer than 30 days for the state-mandated units and § 66333(g) the same for a junior ADU, so a tenancy of exactly 30 days is allowed by the local text and barred by the statute. Write the lease for 31 days or more.

The trusted benchmark is HUD’s Fair Market Rent for the Los Angeles–Long Beach–Glendale metro area. Read it as a floor rather than a forecast, and in Rolling Hills read it as a low floor: the figure is calculated across all of Los Angeles County and every age and class of housing stock, so a new detached unit on an acre lot inside a gated city is not the property it describes.

HUD Fair Market Rents for the Los Angeles–Long Beach–Glendale HUD Metro FMR Area, FY 2026 as revised, effective May 21, 2026 (91 FR 21301). HUD’s FY 2027 figures take effect October 1, 2026. Treat these as a floor rather than a forecast: a new, fully permitted detached ADU typically rents well above the metro benchmark, because the comparison pool includes much older and smaller stock from across the whole county.

Why the Rolling Hills market rewards the investment

Rolling Hills is the smallest kind of market and one of the strongest per lot. The city is roughly 1,600 residents on parcels with a one-acre minimum in RA-S-1 and a two-acre minimum in RA-S-2, and a minimum lot width of 150 feet at any point (§ 17.16.060), which means nearly every property has the physical room for a 1,000-square-foot detached unit without touching the house. That is unusual. In most of Los Angeles County the binding constraint on an ADU is land. Here it is sanitation capacity, ground conditions and the design-matching rules — and all three are knowable before anyone digs.

The uses follow the market rather than the rent table. Multigenerational housing, staff accommodation, a guest unit that is legally a dwelling rather than a permanently kitchen-less “guest house,” a studio or office detached from the main house — these are the briefs that come up on an estate lot, and all of them are better served by a permitted ADU than by an accessory structure that needs a conditional use permit and a public hearing to exceed 200 square feet (§ 17.16.040(A)(3)). Where the property already carries an unpermitted unit built before January 1, 2020, § 17.28.080(B) provides a legalization path the City may not refuse on the ground that the unit fails current building standards or Chapter 17.28 itself. State law adds two protections the local text does not spell out: Gov. Code § 66311.7(e) bars impact fees and connection or capacity charges on a legalization permit, except where utility work is needed to meet Health & Safety Code § 17920.3, and § 66311.7(f) bars penalizing you for the unpermitted unit. Section 66311.7(d) adds the most useful right of the three: the City must publish a checklist of the Health & Safety Code § 17920.3 substandard conditions, and must tell homeowners they may obtain a confidential third-party code inspection before applying — so you can find out what the unit needs without putting it on the City’s radar first.

When an ADU isn’t the right move

Four situations where the honest answer in Rolling Hills is wait, change the plan, or do something else.

The rules that make Rolling Hills different

This is the part of the page that does not exist anywhere else, so it is worth being precise about what is settled and what is not. Everything below is sourced to RHMC Chapters 17.16, 17.28 and 17.46, the City’s own published planning materials, Gov. Code §§ 66314–66326, and Civ. Code §§ 714.3 and 4751.

No sewer: the septic question that comes first

Rolling Hills has no municipal sanitary sewer network. The City surveyed residents about sanitation collection in 2021 and publishes homeowner guidance on septic systems and cesspools and on the Los Angeles County environmental health review of a septic system. For an ADU, that fact becomes a rule: § 17.28.050(F) provides that where the ADU or junior ADU will connect to an onsite wastewater treatment system, the owner must include with the application a percolation test completed within the last five years — or, if the test has been recertified, within the last ten. That is not a local invention and it is not preempted: Gov. Code § 66323(f) expressly authorises a local agency to require exactly this, in these words, even for the state-mandated units.

The form is the easy part. The substance is that a system engineered for one house is now being asked to serve two dwellings, and whether it can is a question about your leach field, your soil and your lot, not about the ordinance. This is the most common reason a Rolling Hills ADU stalls, and it is also the cheapest problem on the project to discover early. A septic evaluation ahead of design tells you whether you are building an ADU, building an ADU and a new system, or not building yet. None of the other decisions can be made properly without that answer.

The association, the covenants and what the City published

Rolling Hills is a gated city, and the gates are not the City’s. The Rolling Hills Community Association is a private corporation with an independently elected board that owns and maintains the roadways, easements and trails inside the city, manages access at the gates, and administers recorded covenants that run with most of the land. Those covenants limit density to one residence per lot and require construction to follow a traditional California ranch and equestrian architectural vocabulary. The zoning code defers to the Association in terms: RHMC § 17.16.150 provides that structures permitted in setbacks “are also subject to approval by the Association,” and § 17.16.070(A)(2) excludes from impervious-surface coverage paving “maintained by the Association.”

The City goes further than that in its own published planning FAQ, which answers the question “What is the permitted building height?” with: “Only a single story structure with height regulated by the RHCA.” That page is undated and is stale on its own terms — the City codified a 21-foot figure at § 17.16.080(A)(1) when it adopted Ordinance No. 386 in July 2025 — but it is the City’s own description of how development review works here, and it points a homeowner at a private association for a development standard.

The practical advice follows from the split. Treat the Association review as a real project requirement, because it is one, and start it early and in parallel. Treat the City’s statutory clock as a separate thing that runs on its own terms. If the City declines to accept an application as complete solely for want of Association sign-off, that is the moment to ask, politely and in writing, which provision of Chapter 17.28 the application fails.

Site plan review, and why it does not reach a conforming ADU

The RA-S zone runs on discretionary review. Section 17.16.050 states that site plan review is required for development in the zone, and the City’s published FAQ lists “any new building or structure except barn/stable without grading” among the triggers. Site plan review under Chapter 17.46 is, by the City’s own description, a discretionary process before the Planning Commission. A cabana, guest house or recreation room over 200 square feet needs a conditional use permit and a public hearing on top of that (§ 17.16.040(A)(3)).

None of that reaches a conforming ADU, and the City’s own ADU chapter says so. Section 17.28.040(A)(3)(b) provides that ministerial permits for an ADU or JADU “are considered and approved without discretionary review or a hearing,” which is what Gov. Code § 66317(a) requires, and § 66317(c) forecloses any other local regulation being used to delay or deny. Chapter 17.28 points the same way from the other direction: § 17.28.090 offers a conditional use permit as a route for an ADU that does not conform to the objective standards in §§ 17.28.010 through 17.28.080. That is a strong implication rather than an express statement — the operative authority is Gov. Code § 66317(a), which makes ministerial approval mandatory, and § 66323(b), which bars any standard § 66323 does not authorise on a Class 1 unit.

The contrast is worth naming, because it is the strongest practical argument for building an ADU here rather than an accessory structure. A 900-square-foot guest house in Rolling Hills is a conditional use permit, a public hearing and a structure that may never legally contain a kitchen. A 900-square-foot ADU is a ministerial permit with a 60-day clock and a full kitchen. Same building, different instrument, very different process.

An open question worth asking the City

One thing on this page is unresolved, and we would rather flag it than write around it. On December 5, 2025, HCD sent the City a Letter of Technical Assistance stating that “[t]he most recent ADU ordinance on file for the City with the California Department of Housing and Community Development (HCD) is from 2020,” that the ordinance “may be outdated and out of compliance with State ADU Law,” and that if HCD’s records were incorrect and a new ordinance had been adopted, the City should submit it to the ADU Portal. Ordinance No. 385 had been adopted more than a year earlier, on November 25, 2024.

Gov. Code § 66326(a) requires a local agency to submit its ADU ordinance to HCD within 60 days after adoption, and § 66326(d) provides that an ordinance not submitted within that window “shall be null and void,” with the agency required thereafter to apply the state standards until it adopts a compliant ordinance including the submittal requirement. Whether that is engaged here we cannot say from outside: HCD’s letter records what its own files showed in December 2025, not a finding that the City failed to submit, and records can lag.

For most homeowners the question is academic in the best possible way. Chapter 17.28 tracks the state floors closely — the unit stack, the heights, the 800-square-foot protection, the fee exemptions, the AB 1154 junior-ADU rule — so the standards the City would have to apply under § 66326(d) are largely the standards it already applies. It matters only where the local chapter is stricter than the state floor: the architectural matching and glazing rules at § 17.28.060(H), the 30-foot front setback, and the floor-area and open-space caps. If one of those is the thing standing between you and the unit you want, it is worth asking the City in writing when Ordinance No. 385 was submitted to HCD.

Historic resources, and the private-street twist

Section 17.28.060(I) provides that an ADU on or within 600 feet of real property listed in the California Register of Historical Resources must be located so as not to be visible from any public right-of-way. The rule is conventional; its application here is not. The roadways inside Rolling Hills are private, owned and maintained by the Association rather than dedicated to the public, so on most lots there may be no public right-of-way within 600 feet from which the unit could be visible. Whether the provision therefore has any practical effect on a given parcel is a question for Planning, and one worth asking early if your property is near a listed resource rather than assuming a screening requirement you may not have.

Wildfire, sprinklers and ground movement

Rolling Hills takes wildfire seriously as a matter of civic programming — the City runs sirens and SAFE units, a block captain programme, home hardening and canyon management guidance, defensible space and plant selection standards, and publishes a wildfire insurance letter for residents. Fire hazard severity zone mapping bears on construction assemblies, defensible space and access rather than on entitlement, and the tier that governs your build is a parcel-level fact: check your specific address against the Office of the State Fire Marshal’s fire hazard severity zone viewer rather than relying on a citywide shorthand.

What none of it does is stop you building. There is no categorical wildfire prohibition on ADUs in Rolling Hills, and the ordinance handles sprinklers in the homeowner’s favour: sprinklers are required in an ADU or junior ADU only if they are required in the primary residence, and constructing an ADU does not trigger a sprinkler retrofit in the existing house (§ 17.28.050(C); Gov. Code § 66314(d)(12)). The City also requires a Class A, non-reflective roof assembly.

Ground movement is the other physical constraint and the one more likely to change your budget. The City maintains a land movement update programme and resident resources, and its planning FAQ states that soils and geology reports are required for all projects. Treat the geotechnical report as a gating item rather than a submittal formality.

Where the local text and state law diverge

Chapter 17.28 is unusually clean — it already carries AB 1154, SB 1211 and the SB 543 completeness clock. Three divergences are worth knowing about anyway.

Recent state-law changes and where Rolling Hills stands

Because Ordinance No. 385 was adopted in late 2024 and amended again in December 2025, the chapter incorporates amendments many Los Angeles County ordinances are still behind on.