A second-story addition in Los Angeles runs about $400 to $600 per square foot in 2026, so adding 800 square feet upstairs typically costs $320,000 to $480,000. That includes reinforcing the structure below, a new roof, the stairs, and the drawings and permits.
Where the money goes before you get a second floor
The foundation and first-floor walls usually need reinforcement before anything can sit on top: new footings, shear walls, posts and beams. The existing roof comes off and a temporary one goes on to keep the rain out. A staircase eats floor area downstairs. Only then do you start building the thing you are paying for.
When it makes sense anyway
Small lots where building out would take the whole yard. Hillside lots where there is nowhere to go but up. Neighborhoods where a second-floor view adds real value. If you have the lot area, building out is typically 25 to 40 percent cheaper per square foot.
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.
