A ground-floor room addition in Los Angeles costs about $300 to $500 per square foot in 2026, including drawings and permits, so a 400 square foot bedroom and bathroom addition typically runs $150,000 to $250,000. Simple additions can come in near $250 per square foot, and complicated or hillside ones run past $600.
Why additions cost more per foot than a new house
A small project carries the same fixed costs as a big one: drawings, permits, getting a crew mobilized, tying into utilities. Spread over 400 square feet instead of 3,000, that adds up fast. And an addition has to attach to a building that was never designed for it.
What is in that number
Drawings, structural engineering, city fees, foundation, framing, roofing, matching the exterior, electrical, plumbing, heating and air, insulation, drywall, windows, doors, flooring and paint. A bathroom in the addition adds $25,000 to $50,000 on top.
How to keep it down
Keep the shape simple and rectangular. Line it up with the existing roofline. Avoid relocating the main electrical panel or the sewer line. And build out rather than up if your lot has the room.
Los Angeles County figures, reviewed 2026-10-29 by America General Contractors, California contractor licence CSLB 1083262. Planning ranges, not a quote, and not legal advice. We confirm the current rules for your parcel before anything gets drawn.
Related questions
- How long does a room addition take?
- How much does a second story addition cost?
- Does a remodel increase property taxes in California?
