The first place to start with home additions plans in Bay Area, San Jose is determining what your budget will be for the project and estimating how much the project will cost. Unfortunately, the total cost will be greatly impacted by the type of addition you want to build. The cost of home additions in the San Francisco, San Jose, and greater Bay Area of California is higher than the rest of the United States costing around $350-500 per square foot. 

The professional contractors at Top Home Builders have created this informational guide to identify how much does an addition cost in Bay Area, San Jose, the cost of different types of home additions, the best home additions that will increase property value, factors that affect costs, and so much more.

Why is Adding a Home Addition so Expensive?

Adding an addition to a house in the Bay Area, San Jose can be expensive due to the complexity and scale of the project. Where remodeling projects generally cost much less because the existing exterior skin of the home typically isn’t impacted, home additions on the other hand are much more likely to involve the exterior structure. 


Make sure you pick the right home-building team to implement your project because they can help you stick to your budget and schedule. It’s important to note choosing low-bid contractors can result in them charging you for any minor changes, setbacks, or complications. In addition, poor management can lead to frustration while waiting for your project to be completed, or schedule delays that cause you additional costs. 

Low-cost materials can also be problematic because they wear out quickly. The materials, finishes, fixtures, or appliances could be outdated or worn out before you ever resell your home, resulting in extra costs for having to replace them or reduced market resell value. With the right design and construction team on your side, they can help guide you through the process and make sure you are happy with the end results without breaking the bank to do so.

Best Home Additions that will Increase Property Value

When deciding how you want to renovate your house, consider which home additions are most likely to increase your property value. By adding an addition to a house in Bay Area, San Jose, you are increasing its value as an asset. It’s also worth considering which investment would be most beneficial to you when or if you decide to resell your home in the future. 

One of the top home additions that increase property value is adding a finished basement to your home. The average cost to finish a basement in the Bay Area is about $28,400, but the costs range between $7,800 to $64,000. A low-end home addition includes just adding a little paint or drywall, whereas a higher end home addition includes installing sump pumps, waterproofing the structure, or building walls and finishing the entire floor. 

Adding a detached garage can also increase property value significantly. Many homeowners may decide to add a detached suite above a garage, which can be used for guests, office space, or kid’s playhouse. If your home is ever on the market for sale, detached garages can increase interest in your home, which results in higher, more competitive offers. You can expect $30-55 per square foot as the average cost for a detached garage, and the average total cost for a two-car garage would be anywhere between $11,800-$19,000.  


Different Home Additions + Prices

Home addition costs will vary based on their common design features. For example, kitchens and bathrooms and kitchens require extensive plumbing whereas living room additions will require more space. Here is a breakdown of the different home additions and their average costs.

Room AdditionAverage Cost
Garage or shed$3,800
Living Room$30,000
Additional Story$145,000

How Much Does Home Addition Cost?

The average cost of a home addition is $46,000, with the price ranging from $21,000 to $75,000. High-end finishes, specialized fixtures, and unique architectural features can increase the total costs well into the hundreds of thousands of dollars.

How Much Does Adding Second Storey Addition Cost?

Adding an entirely new floor to your house is considered a large-scale home renovation. On average, the cost to add a second story in Bay Area, San Jose is anywhere between $90,000 and $200,000 depending on which rooms you choose to install and the size of your house.

How Much to Add a Bathroom?

If you live in a house with a larger family or several roommates, you know the importance of having multiple bathrooms. Since a home with more than one restroom is a popular choice among homeowners, adding a second bathroom does help increase its market value. 

The Cost vs Value 2020 Report notes that for an upscale 100 square foot bathroom addition, the average total costs approximately $120,160 in the Bay Area, averaging to about $1,202 per square foot. This does assume however that the bathroom is finished with upscale finishes and fixtures. A mid-range bathroom costs nearly half the price, at around $67,378. This cost is based on a 6×8 size bathroom addition, resulting in a rate of $1,400. You’ll notice this is a higher cost per square foot than the upscale bathroom addition.

One of the reasons why the midrange bathroom costs more per square foot than the upscale version is because regardless of how large the bathroom is or how high-end the fixtures are, the plumbing connections for a sink, toilet, and shower or tub in a single restroom doesn’t change. In fact, the costs will typically be lower per square foot if the project is larger. When making home addition plans for a bathroom, consider adding bedroom space or extra living space to get the most value out of your renovation.

How Much Does Adding Second Storey Addition Cost?

The cheapest addition and the one that’s easiest to implement for your home is a simple bedroom addition. According to the Cost vs Value 2020 Report, the average room addition cost in Bay Area, San Jose is approximately $375,000 for an upscale 640 square foot bedroom addition. This averages to about $585 per square foot. The cost of the upscale bedroom features a master bathroom, including a walk-in shower, soaking tub, high-end fixtures, and a hospitality bar.

A mid-range bedroom suite costs nearly half the price, around $187,000 on average. This cost is based on a 384 square foot area, resulting in a rate of $490 per sq. ft. A master bathroom is also included in a mid-range bedroom suite however, the fixtures are much lower end.

The additional bedroom addition cost will be lower without the extra bathroom. Even if you have to reinforce some of the structure below, the cost to add a second story in Bay Area, San Jose will be much less expensive than building a new foundation to the side of your home. According to HomeAdvisor, the average room addition costs between $300-$450 per square foot in the Bay area so a 400sqft room could range between $120,000-$180,000.

How Much Does a Kitchen Addition Cost?

There is significant value in including a kitchen addition for your home. By opening up the floor plan and creating an open space between the dining area, living room, and kitchen, you are optimizing your existing layout to improve functionality. 

Kitchen additions are more expensive of a renovation than a kitchen remodel because there are costs for cabinetry, interior finishes, plumbers, and electricians, as well as for exterior finishes, the extra foundations, site work, and roofing. You may want to consider adding additional living space instead of opting for a kitchen addition. This way you can keep the overall costs down by making use of your existing power connections and plumbing to remodel your existing kitchen space.

Factors Affecting Price

The most accurate way to determine your estimated home addition cost will be through working with certified home builder contractors. Only these experienced professionals will be able to break down the costs for you and build a budget with your specifics in mind.

With that said, there are many factors that costs with some home addition cost factors standing out more clearly than others. The type, size, and design of a home addition make the greatest impact in affecting costs, yet many local and labor-related prices have an influence as well. Let’s take a closer look at which factors affect price the most.

Project Size and Scope

Home addition costs per square foot will vary based on the placement of your home, the type of room you’re envisioning, and the materials chosen.

The average price per square foot for a home addition is $140, and this general range includes factors such as local permits, siding, general contractor and architect fees, framing, insulation, foundation, roofing, flooring, electrical, finishes, and plumbing.


Location of the Addition

The location of your home addition greatly impacts pricing. Here are a few examples of the type of questions you want to consider:

  • Are you adding to the back of the house? 
  • Is the addition going over the garage?
  • Which floor is the addition on in your home?
  • Will the HVAC ventwork be interrupted by the addition?
  • Does the new room attach to existing wiring and plumbing?
  • Will the addition affect your landscape?
  • Will you need to accomodate the addition by moving structures in your yard?


Labor accounts for approximately 50% to 60% of the home addition cost in Bay Area, San Jose. Licensed professionals are required to take on majority of the work. Here are just some of the main professionals that will likely be involved in your home addition project and their standard rates.

Labor Cost
General Contractor10% – 20% of the total cost
Architect5% – 10% of the total cost
Structural Engineer$100 – $350 per hour
Plumber$45 – $200 per hour
Electrician$50 – $150 per hour
Carpenter$75 – $100 per hour
Painter$20 – $100 per hour
HVAC Expert$50 – $100 per hour


To get a better idea of how much does an addition cost in Bay Area, San Jose, it’s best to break down your dream design according to materials. Because every design is unique, it’s important to calculate your specialized costs so you can avoid guessing where your total home addition price will land.

Materials Cost
Flooring$1 to $10 per square foot
Insulation$1.50 to $5.00 per square foot
Drywall$2.50 per square foot
Foundation$4 to $100 per square foot
Framing$400 to $1,500 per 1,000 feet
Rough-in plumbing$400 to $1,800


When adding a new structure to your home, make sure to include the cost of building permits. While smaller permits – for installing new plumbing or removing a wall – can cost around $200, building a new structure can push permit costs up to $3,000.

Zoning Laws

We all want to dream big when designing our home addition plans, however our ideas will have to feasibly align with local building and zoning laws. For example, sewer drainage, access to utilities, and distance from your property line are variables that will also need to be considered.

Building Up vs. Building Out

Building out always costs more than building up. Laying a foundation will significantly tip the scales of increasing your costs compared to adding a roof and framing to an existing structure.

Site Preparation

On average, you can expect to pay $1,500 to $5,000 when preparing your land for a first-floor buildout, or $1 to $5 per square foot for the basic cost of land clearing. Please note that this does not include excavation costs and the price to pour concrete for a new foundation.

Hard Costs

Hard costs refer to anything considered direct construction costs. Any expenses from the process of construction and the physical construction of adding an addition to a house. This includes equipment, labor, materials, and other expenses needed for construction. A few examples of hard costs are steel, lumber, electrical, plumbing, and masonry.

Though a hard cost generally only occurs during construction while the work is ongoing, there may be some early expenses to mobilize contractors or purchase materials. For labor costs to remain at the estimated amount, it’s important for construction projects to run on schedule.


Soft Costs

Soft costs are all the other expenses involved in a renovation project that do not deal with the process of construction or the physical construction itself. Fees, services, and insurance are common examples of the non-tangible items that make up most soft costs. Home addition soft costs can include design services such engineers, interior decorators, designers, and other design consultations, building permits and property surveys, equipment rentals, property insurance, general liability insurance, workers compensation, and builders risk coverage, marketing, maintenance, loan-generated interest, bank transaction fees, and accounting expenses, legal fees, and project management expenses.

Soft costs happen from the preplanning stage of a project to post-occupancy and beyond. Soft costs typically are important to include in project budgets because they can make up 25 – 50% of the total project budget. Quantifying them early in the project is also important so you can calculate your final project delivery return on investment.

Related Article: Home Additions That Increase Home Value

Ready to Build a Home Addition in the Bay Area?

Planning a home addition in the Bay Area can be complex and costly, with prices influenced by various factors. By partnering with Top Home Builders, we’ll make sure your home addition is built according to your budget and lifestyle.

Contact us today for a free consultation and start transforming your home with confidence.