Home Addition Cost in San Francisco [2025 Data]

Normal Range: $40,256 - $177,591

A home addition costs an average of $106,843 in San Francisco, California. Depending on the location, size, type, and materials, most homeowners spend between $40,256 and $177,591.

How we get this data
Large and open living room leading into sunroom with windows on two sides and lots of natural light flowing in. There is a window seat on one side and a leather couch and plant on the other.
Ursula Page / Adobe Stock Photography
Large and open living room leading into sunroom with windows on two sides and lots of natural light flowing in. There is a window seat on one side and a leather couch and plant on the other.
Ursula Page / Adobe Stock Photography
Highlights
  • San Francisco homeowners will pay more than the national average for a home addition due to the city’s high cost of living. 

  • The relatively small average lot size in San Francisco may make building up more feasible than building out. 

  • The cost of a home addition depends on the size and type of additions, materials used, labor costs, and more. 

If you’re feeling a little cramped in your San Francisco home, a home addition may be the answer. Because of San Francisco’s high cost of living, homeowners can expect to pay a higher cost for a home addition—a little more than twice the national average. The average home addition in San Francisco costs $106,843, with most homeowners paying between $40,256 and $177,591. We break down some of the project costs so you can budget accurately for this project.

Home Addition Cost Factors 

The cost of building a home addition in San Francisco, CA, depends on factors like the size of the addition, how you plan to use the space, what materials you choose, whether you build up onto another story or out at ground level, and more. Take a look at some of the things that will affect your total project cost. 

Size

Home additions in San Francisco cost between $160 and $400 per square foot if you’re building out and between $600 and $1000 per square foot if you’re building up. The cost to add a 10x10 room to a house costs an average of $25,000 if you build out and $80,000 if you build up.

Where in those ranges your total falls also depends on the complexity of the room and its finishes. For example, adding a bathroom will often cost more than a bedroom since it requires additional plumbing and electrical work. The size of the addition can also affect how long the addition takes to build, which can add to your labor costs for larger projects.

Price Notice

Remember that if you add square footage to your home, the cost of your homeowners insurance will increase accordingly. Before you embark on this project, speak to your insurance company about expected costs.

San Francisco has a relatively small average lot size at around 2,700 square feet and an average house size of just under 1,500 square feet, so if there isn’t room to spare on your lot, you may need to build up onto another story rather than out with a bump-out addition.

Addition Size (Sq. Ft.)Bump-Out BuildSecond Story Build
60$10,000–$25,075$37,625–$62,700
80$13,375–$33,450$50,150–$83,600
100$16,700–$41,800$62,700–$104,500
150$25,050–$62,700$67,500–$156,750
200$33,400–$83,600$125,400–$209,000
300$50,100–$125,400$188,100–$313,500
400$66,800–$167,200$250,800–$418,000

Materials

As you can imagine, it takes many kinds of building materials to complete a custom home addition. Material prices vary widely, so your price could push closer to $177,591 if you choose luxury or high-end materials at each step of the way.

Framing Materials Cost:

Framing MaterialAverage Cost per Sq. Ft.ProsCons
Wood$1–$5Cost-effective, easy to installFire risk, prone to pests and moisture problems
Steel$2–$4Durable, fire-resistantComplex installation, limits roof design

Insulation Materials Cost:

Insulation MaterialAverage Cost per Sq. Ft.ProsCons
Blown-in$0.50–$2.30Low-cost, fast installationProne to water damage, less durable
Fiberglass$0.30–$1.50Fire-resistant, cost-effectiveLower R-value, easily damaged
Spray foam$1.50–$4.90High R-value, resists pests and moistureHigher cost, more flammable
Rockwool$1.10–$3.10Durable, high R-valueLoose fibers can be a health risk, higher cost

Roofing Materials Cost:

Roofing MaterialAverage Cost per Sq. Ft.ProsCons
Asphalt shingles$1–$1.20Affordable, easy to installProne to granule loss, shorter lifespan
Metal$5–$16Long lifespan, low-maintenanceHigher cost, difficult to repair
Slate$10–$30Longest lifespan, high-end aestheticsVery heavy, difficult to install/repair
Synthetic$5–$12Durable, lightweightVariable quality, may look engineered

Flooring Materials Cost:

Flooring MaterialAverage Cost per Sq. Ft. ProsCons
HardwoodLong-lasting, many available optionsHigher cost, prone to dents and scratches
LaminateBudget-friendly, easy to installDifficult to repair, prone to water damage
TileVariety of options, easy to cleanMore expensive, complex installation
CarpetRetains warmth, soft to walk onDifficult to keep clean absorbs odors

Siding Materials Cost

Siding MaterialAverage Cost per Sq. Ft.ProsCons
Vinyl$3–$12Budget-friendly, easy to installShorter lifespan, prone to impact damage
Fiber cement$5–$14Extremely durable, long lifespanHigher cost, difficult to repair
Wood$2–$6Eco-friendly, wide range of stylesProne to rot and pest damage, high-maintenance

Type

4 popular home extensions compared by average time of completion, with a porch taking 3 to 4 weeks to complete

The cost to add on a room varies based on the type and size of the room you’re building. Rooms like kitchens and bathrooms require plumbing work that a bedroom doesn’t, while an unfinished attic home addition may not require electrical or HVAC work that a bedroom needs. The cost per square foot for your home addition will vary based on utilities and the finishes required for how you plan on using the extra square footage.

Addition TypeAverage Cost Range
Attic$83,600–$96,150
Bathroom$73,150–$84,125
Bedroom$130,625–$150,225
Dining room$62,700–$72,100
Kitchen$114,950–$132,200
Laundry room$16,720–$19,225
Living room$62,700–$72,100
Mudroom$25,075–$28,850
Sunroom$98,225–$112,850
Detached garage$55,175–$63,550
In-law suite$172,950–$199,000
Second story$365,750–$420,100

Site Prep

On average, site prep for a home addition costs between $3,000 and $10,000. You may not need any site prep in some cases, while other home addition projects may require grading land, demolishing concrete patios, removing trees, and other work that can add to your total.

Permits

Before you start construction, you’ll need a building permit for your addition from the San Francisco Department of Building Inspection. Permit fees vary based on the cost of your project—a permit for an addition with the average cost of $106,843 will be around $2,800, but you may pay anywhere between $600 and $9,000 in permit fees, depending on the scope of your project. Failure to obtain the proper permits can result in hefty penalties, up to nine times the applicable permit fee, so ensure getting the proper permits before beginning work is on your home addition project checklist

Home Addition Pro Costs

Home Builder Pro Costs

Total labor costs will make up about 40% to 60% of your project costs, and hiring a general contractor or homebuilder in San Francisco, CA, will cost around 10% to 20%. Hiring a qualified pro to manage your build can make the job go smoothly—they can coordinate subcontractors, ensure the project stays on schedule and budget, answer your home addition questions, and confirm the build complies with all local codes and regulations. 

Additional Pros to Consider Hiring

Building an addition requires various pros in order to complete the work. Over the course of your project, you may need to bring in a structural engineer to confirm your plans are structurally sound, an electrician and plumber to run utilities to the new space, and a carpenter and interior painter for finish work. Here are some of the pros you may need to hire when you’re building an addition: 

Does a Home Addition Increase Property Value?

Home additions add value to your property and offer a return on investment (ROI) of 20% to 50% on average. San Francisco’s competitive housing market and relatively small average home size mean that homes with valuable added square footage can command a higher price when it’s time to sell. 

How Angi Gets Its Cost Data

Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We survey real Angi customers about their project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects. 

Want to help us improve our cost data? Send us a recent project quote to [email protected]. Quotes and personal information will not be shared publicly.

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