Building an ADU in Signal Hill. Rules, costs, timeline.

Can I build an ADU in Signal Hill?

Five things to know before you start

If you read nothing else here, read these. They are the five points that change the most projects in this city.

How many units your lot can take

Everything in this section is grounded in the California Government Code, which governs a Signal Hill ADU directly because the City has adopted no ordinance of its own. We won’t re-anchor that on every line; assume it under each subsection unless we say otherwise.

Gov. Code § 66323(a)(1)–(2) lets a single-family lot combine three units: a conversion ADU carved from existing space in the house or an accessory structure, a JADU of up to 500 sqft inside the house, and a new detached ADU of up to 800 sqft with 4-foot setbacks. The HCD ADU Handbook (March 2026), p. 17 confirms it. That is up to two ADUs plus a junior ADU. State law separately requires the City to allow at least one ordinance ADU under Gov. Code § 66314 — the larger unit, which here runs to the 1,200 sqft state default. And there is no minimum lot size, because Gov. Code § 66314(b)(1) bars one.

On a lot with an existing multifamily building, the SB 1211 counts apply as written: conversion ADUs in non-livable space, at least one and up to 25% of the existing unit count (Gov. Code § 66323(a)(3)(B)), and up to eight detached ADUs, capped at the number of existing units (Gov. Code § 66323(a)(4)(A)(ii)). JADUs are a single-family product only.

Owner-occupancy

You do not have to live on the property to build or rent an ADU here. Gov. Code § 66315 forbids a city from requiring it, and with no local ordinance that rule applies directly, with nothing layered on top. An investment build and a family-flex build are treated the same way.

What an ADU costs in Signal Hill (2026)

Our Signature plans are fixed-price — architectural design and full permit processing included, the same number whether the lot sits on the hill, on the flats, or across the line in Long Beach. 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.

The two-story models are shown for reference. In Signal Hill the detached envelope is single story, so the Lincoln at 1,000 sqft is the practical ceiling as drawn — comfortably inside the 1,200-square-foot state default. Custom work is priced per project, $9,990–$19,990 for design and permit processing.

City fees and pass-throughs

A conforming ADU is a ministerial permit, so there is no entitlement to win first. Per the City’s Schedule of Fees and Charges effective July 1, 2026, planning review for an ADU is a $3,584 deposit against actual cost. The schedule’s own footnote on that line says the deposit covers methane review as well as planning review. Building permits are valuation-based: in the $100,001 to $500,000 tier, $2,101.07 for the first $100,000 plus $11.56 for each additional $1,000. Plan check runs 85% of the building permit fee and includes up to three plan checks.

Two oil-field line items sit outside that. The Methane Site Testing and Mitigation Permit is $864 per well plus consultant costs. And the assessment itself — the registered geologist’s fieldwork and stamped report — is a separate consultant cost, as is a sub-slab membrane and vent system if the assessment calls for one. Impact fees are exempt for an ADU of 750 sqft or less and proportional above (Gov. Code § 66311.5(c)(1)).

What it returns: renting your ADU

Long-term rental only. For a rent benchmark the government figure is HUD’s Fair Market Rent for the Los Angeles–Long Beach–Glendale HUD Metro FMR Area, which covers Signal Hill. For FY 2026, as revised effective May 21, 2026: $2,079 for a studio, $2,328 for a one-bedroom, $2,903 for a two-bedroom, and $3,681 for a three-bedroom. Those are metro-wide figures spanning the full range of housing stock and unit ages, so treat them as a floor rather than a forecast.

Signal Hill’s rental drivers are unusual for a city of roughly twelve thousand people. It is surrounded on every side by Long Beach, so it draws on that whole rental market while keeping its own small-city services. It sits minutes from Long Beach Airport, Cal State Long Beach, and the Long Beach medical corridor. And the hill itself carries some of the best views in the area, which a well-sited unit can capture. A newly built detached ADU here typically rents above FMR — but we would rather point you at a verifiable number than an invented one, and a local property manager can price your specific street.

HUD FMR figures: FY 2026 Fair Market Rents, Los Angeles–Long Beach–Glendale HUD Metro FMR Area, as revised effective May 21, 2026 (91 Fed. Reg. 21301). Your ADU’s actual performance depends on finish level, lot, access, and the rental market at the time you lease it. For payback math keyed to your lot, use the ADU ROI calculator or the ADU calculator.

When an ADU isn’t the right move

Not every Signal Hill property is a good ADU candidate, and it is cheaper to learn that now than after you have paid for plans. Four situations where we would tell you to wait, pick a different unit type, or not build:

• Your numbers depend on short-term rental income. They will not work. State law requires a rental term longer than 30 days for a § 66323 unit — it is mandatory, not a local option. Run the math on a 30-day-plus tenancy or reconsider.
• You want a separate-sale exit. With no ADU ordinance there is no AB 1033 opt-in, so the unit cannot be sold apart from the house. If a condominium exit is the plan, this is the wrong jurisdiction for it.
• Your buildable pad disappears once the wells are located. On some parcels the fire-code access around a well leaves nothing worth building on in the rear yard. A conversion inside an existing structure is usually the better move, and we would rather find that in the lot study than in plan check.
• You need two stories of detached space exactly as our stock plans draw it. The detached envelope is 16 feet. The honest routes are a single-story plan, a modified two-story plan, or a custom design — not a variance, which takes the project out of ministerial review entirely.

The rules that make Signal Hill different

A city with no ADU ordinance

Most cities in Los Angeles County adopted their own ADU chapter to mirror — and occasionally to shave — state law. Signal Hill never did, and it is direct about the choice. Its published ADU handout opens with the statement that the City “does not have a local Accessory Dwelling Units (ADUs) ordinance and therefore follows the State regulations.” The code says the same thing. Title 20 runs from Chapter 20.02 through Chapter 20.98, and no accessory-dwelling-unit chapter appears in it.

Under Gov. Code §§ 66315 and 66316, a city that adopts no ADU ordinance applies state ADU law directly, and a local rule that conflicts with the statute is void as applied. For a homeowner that is mostly good news:

• You plan against the Government Code. Size, height, setbacks, parking and the review clock all come from §§ 66310–66342 — the same statewide rules that apply in every California city, with no local overlay to decode.
• There is no local layer to argue with. No local floor-area trap, no supplemental design standards, no owner-occupancy covenant, no rental-registration condition. Several neighboring cities have all four.
• Review is ministerial, and the City says so. Its own handout states that state regulations “do not allow discretionary City review, nor Planning review.” The 60-day clock in Gov. Code § 66317 runs, with no hearing and no neighbor sign-off.

Building over the Long Beach Oil Field

This is the part of building here that no state statute prepares you for. The city sits on top of one of the most productive oil fields in California history, and the legacy is physical. Hundreds of wells were drilled across these blocks. Many were plugged and abandoned decades ago and now sit under back yards. The City publishes a list of properties with abandoned wells, and it keeps an Oil Services Coordinator in the Community Development Department for this.

The rule that catches people is SHMC § 16.24.080. Subsection (A) requires the area of development on all properties in the city to be tested for methane gas before a construction or development permit issues, unless the Oil Services Coordinator approves otherwise. That applies whether or not the property contains abandoned wells. The sequence that follows is short and specific:

• Methane site test permit first. No methane test may be conducted without a permit from the Oil Services Coordinator, and the permit is required on all development sites where construction permits are required.
• A registered geologist signs the assessment. The site methane assessment follows the City’s published methane assessment minimum requirements standard and must be signed and stamped by a California registered geologist.
• Thirty days after soils disturbance. The assessment may not be conducted less than 30 days following any soils disturbance on the site — a scheduling constraint, not a formality.
• Mitigation plan if the assessment calls for one. If mitigation is required, or the well access exhibit is labeled “no access & methane mitigation required,” a mitigation plan goes to the Coordinator for approval before any mitigation work begins. In practice that means a membrane and vent system under the slab.

None of that is in tension with ministerial review. Every ADU has to meet the building code and the health-and-safety rules that apply to dwellings generally. A methane barrier under a slab is a construction detail, no different in kind from a vapor retarder or a seismic connection. Expect to build it, and price it in.

Wells, setbacks, and where the unit actually goes

Active and abandoned wells shape siting more than any dimension in this guide. The City requires wells to be located and evaluated by CalGEM — the state oil and gas regulator — before building permits issue, and fire-code access and setbacks around a well then determine where a structure can sit. Where a development is built over an abandoned well, or a well is marked no access, the City’s Title 16 process ends in a recorded declaration disclosing the wells, the leak testing performed, and any methane mitigation installed.

None of that prohibits an ADU. It relocates one. That is the strongest argument for starting a Signal Hill project with a lot study rather than a floor plan. Once the wells are located, the buildable envelope is usually obvious, and a compact single-story unit slots into it cleanly.

The 600-foot noise rule — and where it overreaches

SHMC § 9.16.085 applies to any new development proposing to locate part of a dwelling within 600 feet of an operating oil well, injection well, or appurtenant oil field equipment. The City reviews the oil field map and takes field noise measurements where needed. Where impacts are likely, the applicant submits a noise mitigation plan certified by a state licensed acoustical engineer, showing compliance with the residential noise levels in SHMC § 9.16.020(B). Mitigation can be walls, enclosures, earth berms, construction features, grade changes, or relocating the unit. The noise limit itself is objective, and there is nothing wrong with meeting it.

No separate-sale path

AB 1033 lets a city adopt a local ordinance allowing condominium-style separate sale of an ADU (Gov. Code § 66342). Signal Hill has adopted no ADU ordinance at all, so there is no opt-in and no separate-sale path here. Among LA-area cities only a handful have opted in — Santa Monica (SMMC § 9.31.026) and Culver City (CCMC § 17.400.096) among them. Build here for rental income, family housing, or long-term value.

Oil-field conditions are lot-specific, and this section is general guidance rather than a site assessment. The City’s well list, the access exhibit, and the methane result for your specific parcel govern.