ADUs & Additions in San Dimas

City of San Dimas Community Development Department, Building and Safety Division. Under Municipal Code Chapter 18.12, no building or structure may be built, altered or enlarged until its development plan has been reviewed and approved. Planning Division staff approve pools and spas (with or without retaining walls), ADUs and junior ADUs, and one-story additions designed to match the existing house; new homes, additions of more than one story, and patios, gazebos or ground-level decks that use cantilevers or retaining walls and are visible from a public right-of-way go to the Director of Community Development. The Director can send a staff-level project to a higher level of review when it could be incompatible with, or adversely affect, surrounding property. In the SF-H Single-Family Hillside Zone, a development plan must be approved before any grading or building, and grading or building permit applications there must include site plans, conceptual house elevations and grading plans. We prepare the drawings, make the submittal and handle plan-check corrections ourselves, so you are not the one chasing plan check.

Residential lots here fall under zones with very different rules. The SF-A agriculture zone permits horses on lots of 16,000 square feet or more, while in the SF-H hillside zone new subdivisions need at least 25,000 square feet of net lot area where the average slope is under 20 percent and a full acre at 20 percent or steeper, with a 140-foot minimum lot width and lot coverage capped at 35 percent. One local condition that shapes the work: CAL FIRE's Local Responsibility Area map dated March 24, 2025 places much of the Northern Foothills, including the canyon terrain around Horsethief Canyon Park and the San Dimas Canyon Nature Center, in a Very High Fire Hazard Severity Zone, and the southern hills around Via Verde and Bonelli Park carry a mix of Very High, High and Moderate designations, while the level ground around downtown sits largely outside the mapped zones.

All of it, including Via Verde, Northern Foothills and Downtown San Dimas. Our crews run every job out of our Cahuenga Pass base in Los Angeles, with our own people on site.

Detached ADU: generally $150,000 to $400,000+ across Southern California. What moves it is square footage, finish level, utility runs, and site access; garage conversions typically run well below a ground-up detached build. We give line-item pricing after seeing the site rather than quoting a number over the phone.

Plan a realistic year. Design and engineering typically take one to three months, city plan check and corrections add several more, and construction usually runs four to eight months depending on size and site access.

Usually yes, and often substantially, because the foundation, walls and roof already exist. The trade-offs are that you lose the garage, and older slabs and framing sometimes need upgrading to meet current code.

California ADU law is designed to allow long-term rental, and an ADU is one of the few ways to add rentable square footage to a single-family lot. Short-term rental rules vary by city, so confirm your local ordinance before counting on that income.

Yes. Plans, engineering, Title 24 and the city submittal are all handled in-house, including responding to plan-check corrections. That is a service we sell on its own, so it is not something we hand off.