Home addition cost in Southern California
Published sources give very different numbers, and they measure different things. Lars Remodel, a San Diego design-build company, says a single-room addition in San Diego has a planning range of $150,000 to $250,000 or more (September 2026). For Orange County, Homeblue says $149 to $298 per square foot (June 2024), and Sea Pointe Construction, a building company, says the average room addition is about $145,000 (January 2026).
Researched October 2026. These are published estimates, not quotes. A price for your job comes from a local business.
What the published figures say
| What it covers | Published figure | Area | Source |
|---|---|---|---|
| Single-room addition, design-build planning range (or more) | $150,000 to $250,000 | San Diego | Lars Remodel (a design-build company)September 2026 |
| Bump-out or small addition (or more) | $100,000 to $130,000 | San Diego | Lars Remodel (a design-build company)September 2026 |
| Primary suite with bathroom (or more) | $275,000 to $400,000 | San Diego | Lars Remodel (a design-build company)September 2026 |
| Second-story addition (or more) | $400,000 to $1,000,000 | San Diego | Lars Remodel (a design-build company)September 2026 |
| Home addition, per square foot | $149 to $298 | Orange County | HomeblueJune 2024 |
| Room addition, average, without extravagant design | $145,000 | Orange County | Sea Pointe Construction (a building company)January 2026 |
| Family room addition, room only | $125,000 to $145,000 | Orange County | Sea Pointe Construction (a building company)January 2026 |
| Home addition, per square foot | $80 to $200 | United States (national) | HomeAdvisorJune 2026 |
| Second-story addition, per square foot | $100 to $300 | United States (national) | HomeAdvisorJune 2026 |
| Most homeowners, whole project (national average is $50,994) | $21,895 to $83,355 | United States (national) | HomeAdvisorJune 2026 |
What the sources say for San Diego
Lars Remodel, a San Diego design-build company, gives planning ranges by type of job. A single-room addition is $150,000 to $250,000 or more. A bump-out or small addition is $100,000 to $130,000 or more. A primary suite with a bathroom is $275,000 to $400,000 or more. A second-story addition is $400,000 to $1,000,000 or more.
Lars Remodel gives no price per square foot. It says small additions can cost more per square foot because design, setup and connections do not shrink with the size of the job. A company's own page also helps it win work.
What the sources say for Orange County
Homeblue says a home addition in Orange County costs $149 to $298 per square foot. That page is from June 2024, so it is older than the others.
Sea Pointe Construction, a building company, says the average room addition in Orange County is about $145,000 without extravagant design. It gives $125,000 to $145,000 for a family room with just the room. These are whole-job totals, so they are not the same kind of figure as a price per square foot.
National figures
HomeAdvisor says a home addition costs $80 to $200 per square foot across the country, and $100 to $300 for a second story. It says most homeowners spend $21,895 to $83,355, with a national average of $50,994.
These are national figures, not Southern California ones. They are far below the local company figures above. We did not blend them.
Why the numbers differ
The sources measure different things. Some give a price per square foot and some give a total for a job. Some are cost sites and some are companies that want your work. The scope matters most: a bump-out, a bedroom with a bathroom and a second story are very different jobs.
Use the ranges to spot a quote that looks far off, not to guess an exact price. Ask each builder what the price includes.
Licences and how to check one
In California, a general building contractor holds the class B licence from the Contractors State License Board (CSLB). The CSLB describes it as work on a structure that needs at least two unrelated building trades or crafts.
To check a licence, use the CSLB's online Check a License page. You can search by licence number or business name. You can also call (800) 321-CSLB (2752). Contractors must put their licence number on business cards, bids and contracts. A written contract is required for home improvement projects over $500.
Local Business America does not check licences, verify businesses or rank them. Please check the CSLB yourself before you hire anyone.
Common questions
- How much does a home addition cost in San Diego?
- Lars Remodel, a design-build company, says a single-room addition has a planning range of $150,000 to $250,000 or more (September 2026). It gives no price per square foot.
- How much does a home addition cost per square foot in Orange County?
- Homeblue says $149 to $298 per square foot, but its page is from June 2024. Sea Pointe Construction gives a total instead: about $145,000 for the average room addition.
- How much does a second-story addition cost?
- Lars Remodel says $400,000 to $1,000,000 or more in San Diego. HomeAdvisor says $100 to $300 per square foot across the country.
- What does a home addition cost across the US?
- HomeAdvisor says $80 to $200 per square foot, and most homeowners spend $21,895 to $83,355. These are national figures.
- Why are the local and national figures so far apart?
- They measure different jobs and come from different kinds of sources, and none of them fully explains how it works out its numbers. Use the ranges as a rough guide and ask builders for written quotes.
- What licence does a general contractor need in California?
- A general building contractor holds the CSLB class B licence. Check it on the CSLB's Check a License page or call (800) 321-CSLB (2752).