Why is building in Signal Hill different?
Oil. Shell struck oil at Alamitos Well No. 1 on June 23, 1921, and the city incorporated in 1924. Signal Hill is completely surrounded by the City of Long Beach, but it runs its own planning and building review.
Because of that history, active and abandoned wells can sit under or near residential lots. The city's municipal code includes an Oil Code (Title 16) that sets standards for building over and around wells.
Do I need to check for oil wells before building an ADU?
Yes, if there is any chance a well is nearby. As of October 2026, the City of Signal Hill says wells must be precisely located and evaluated by CalGEM, the state's oil and gas regulator, before building permits can be issued. Applicants submit a city-approved site plan to CalGEM for review and approval.
Where a project is over or close to an abandoned well, the city's oil and gas FAQ (revised May 2025) lists added reports: a well abandonment report with survey and leak testing, a well access exhibit and an equivalency standard assessment.
Is there a methane requirement?
The same FAQ says a site methane assessment report and mitigation plan applies to projects citywide, with or without known wells, before building permits are issued. We confirm with Signal Hill Community Development whether and how it applies to your ADU, because it can affect the foundation design and the budget.
Does state ADU law still apply in Signal Hill?
Yes. Signal Hill has its own ADU rules in its municipal code, but they must follow state law. As of October 2026, that means, for example, no replacement parking when a garage is converted, 4-foot side and rear setbacks for new detached units, and junior ADUs of up to 500 sq ft inside a home.
What about the hill itself?
Sloped lots can change foundation design, drainage and how materials reach the backyard. A sloped rear yard may favor a garage conversion or attached ADU over new construction. We look at grade and access on the first visit.
How much extra does the oil review add?
It depends on the lot. A lot with no well nearby may need little beyond the standard checks. A lot with a well under or near the build area can need surveys, testing and engineering before permits. We will not quote construction until we know which case you are in.
Related
As of October 2026. Sources: City of Signal Hill history page, "Developing Around Oil Wells" page and Oil and Gas Operations FAQ (rev. May 13, 2025); California Government Code.
See what fits on your Signal Hill lot
Send your address. We check for known wells and the city's review steps before any design work.