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How much does a room addition cost in Los Angeles?
In Los Angeles, a ground-floor room addition typically costs roughly $300 to $600 per square foot in 2026, so a 250 to 350 square foot bedroom or family room commonly lands between $80,000 and $180,000. Second-story additions usually run $400 to $800 per square foot because the existing foundation and framing have to be strengthened to carry the new load, and bathrooms and kitchens inside an addition push the per-foot cost up.
| Ground-floor addition | Roughly $300 – $600 per sq ft |
|---|---|
| Second-story addition | Roughly $400 – $800 per sq ft |
| Typical 250–350 sq ft room | Roughly $80,000 – $180,000 |
| Design, permits and construction | Roughly 6 – 12 months total |
Why additions are priced per square foot
An addition is a small new building attached to an old one: foundation, framing, roof, exterior finish, insulation, electrical, possibly plumbing and HVAC, plus the work of tying it into the existing structure so the roofline, floor levels and finishes match. Those tie-in costs are why a small addition costs more per square foot than a large one.
What moves the number
Ground floor versus second story. A second story needs engineering of the existing foundation and walls, often new footings or shear walls, and temporary roofing while the house is open. Wet rooms. A bathroom inside the addition adds plumbing, waterproofing and tile. Site conditions. Hillside lots, poor soil, mature trees and limited access raise foundation and logistics costs. Matching. Matching 1930s stucco texture, clay tile or original windows costs more than a modern contrast.
Permits and timeline
Additions always require a building permit with plan check, and in Los Angeles the design and permitting phase commonly takes 2 to 4 months before 4 to 8 months of construction. Zoning questions such as setbacks, lot coverage and height should be answered before design starts. Oria Builders (CSLB #1029255) designs and builds additions as one scope, including engineering and permits; confirm zoning limits for your lot with LADBS or your city's planning department.
Related Questions
Is an addition or an ADU a better investment?
An addition expands the main house and its living space; an ADU creates a separate unit that can be rented. Which is better depends on whether you need space or income, and on what your lot allows.
Can I stay home during a room addition?
Usually yes. The addition is built outside the existing envelope and the wall between is opened late in the project, typically for a week or two of disruption.
Do additions need an architect?
Not always. In California a licensed contractor or designer can draw plans for most wood-frame homes of two stories or less, with a licensed engineer stamping the structural work. Complex or multi-story designs often benefit from an architect.
Sources
- Los Angeles Department of Building and Safety
- California Business and Professions Code § 5537 (who may draw plans)
Related
- General contractor in Los Angeles
- Room Additions
- What does a general contractor charge in Los Angeles?
- Can I convert my garage into an ADU in Los Angeles?
- How long does an ADU take to build in Los Angeles?
Answered by Gilad Segev — Founder & Licensed General Contractor, Oria Builders (CSLB #1029255). Last updated October 2, 2026.