ADUs & Additions in Hidden Hills

City of Hidden Hills Building and Safety Department. Permits come from the City of Hidden Hills Building and Safety Department, whose plan check, permit issuance and inspection services are provided under contract by Transtech. The City does not issue a building permit until the Hidden Hills Community Association Architectural Committee has approved the exterior design, and that approval covers dwellings, garages, stables, pools, courts, fences and accessory structures. The community's one-acre minimum building site rule and recorded bridle-trail easements both constrain where structures can physically go. The city falls within a very high fire hazard severity zone under CAL FIRE's 2025 local responsibility area mapping. We prepare the drawings, make the submittal and handle plan-check corrections ourselves, so you are not the one chasing the city.

One-acre minimum building sites, mostly flat to gently rolling, with barns, arenas and long private driveways and enough rear yard to plan a pool, guest structure and equestrian improvements as one project. In practice that means recorded bridle trail easements cross most parcels and dictate where a pool, guest house or perimeter fence can actually be placed..

All of it, including Ashley Ridge, Long Valley Road, Round Meadow, Jed Smith Road. We are based in Los Angeles at Cahuenga Pass, so Hidden Hills is a short run for our crews rather than a job we service from out of the area.

Detached ADU in this market generally runs $150,000 to $400,000+. 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.