How Much Does It Cost to Add a Second Story to Your Home in Seattle, WA? [2026 Data]

The cost to add a second story in Seattle, WA, averages $194,425, with homeowners paying from $88,880 to $666,690, depending on project size, addition type, and complexity. Local pro costs also play a role, with higher rates consistent with the area’s above-average cost of living and strict building permit requirements and fees.

Second-Story Addition Cost Factors

The cost to add a second story in Seattle, WA, depends on the size and type of the addition. Some projects are more complex or high-end, which can add further costs for demolition, landscaping, and other factors.

Second-Story Size

A second-story addition costs between $300 and $600 per square foot on average, but complex projects with high-end materials could reach as high as $800 per square foot.

Addition Type

When you can picture your second-story design idea but can't quite put it into words, take a look at the costs by the type of addition. Every second story will be unique, but they typically fall into one of the following categories:

• Full second story: Building a full second story over your current layout comes with stiffer foundation requirements. You will also spend more on windows, roofing, insulation, and all of the homey features that round out your second floor.

• Partial second story: These additions are popular for their flexibility and comparatively lower costs. They may include a guest bedroom, an extra bathroom, or a flexible space for an office.

• Converting a vaulted ceiling into a second story: A vaulted ceiling adds lots of airy space to a house, but some see all that space and wonder if it could be used differently. If the ceiling is higher, it’s possible to convert it into a partial addition or loft to create usable space. 

• Dormer addition: A dormer is a triangular window space on top of a roof. It is a common addition used to expand an existing second story and give second-story rooms more light and a bigger feel. Dormer costs start at $7,100 but can reach $29,800.

• Add a bonus room above the garage: When adding a room above a garage, square footage matters, but you'll also need to ensure the garage's structure can handle the extra weight. The second floor may also require additional insulation and vapor barriers.

Finish Quality

If you choose higher-end materials, such as stone siding or marble bathroom flooring, expect your costs to be higher than those of builder-grade materials. While some high-end materials reduce maintenance costs, many standard finishes are still durable and save money in the total project price.

Foundation Reinforcement

Depending on the structure of your existing home, your foundation may not be strong enough to support a second-floor addition. You'll want to hire a local structural engineer to evaluate your foundation and see what may be needed to strengthen it.

Foundation support work costs $7,500 or more. Where you live, seasonal weather patterns, and ground characteristics all factor into the amount of work needed. 

Demolition

In many cases, building a second story requires that your contractor remove the roof and then open up walls and ceilings in order to reinforce your home’s framing. Removing a room costs an average of $1,400, and the cost to replace the roof when all is said and done falls between $4.90 and $12.20 per square foot. While designers often work around existing chimneys, the price to remove a chimney for a second story adds an average of $4,700.

Adding a Staircase

Installing the main staircase in your home costs between $2,700 and $4,400, but high-end designs can reach $6,700. General contractors will often include this price in the second-story price estimate, as it's a crucial element of the design. However, the placement of your stairs, the design, and additional elements like carpeting can raise the price.

Landscaping

While not as common, the landscape surrounding your home may change when you add a second story. Construction equipment can damage your lawn, garden, and surrounding trees. Due to a shift in the shadows of your lawn, you may choose to move certain plants and flowers that sat in direct sun before the build. Professional landscaping costs between $5 and $13.30 per square foot.

Temporary Housing

For safety purposes, you'll need to be out of your house during the construction of your second-story addition. A partial addition can take three to six months to complete, while a full second-story addition can take six to 12 months. If you don't have a nearby relative or a motorhome to stay in, factor in the cost of a rental into your project. 

Home Builder Pro Costs

The cost of hiring a local pro home builder in Seattle, WA, varies, depending on labor rates, permits, and taxes.

Labor Rates

Labor rate is one of the main cost drivers for adding a second story in Seattle, WA, and general contractors charge 15% to 20% of the total project cost. This add-on fee usually covers managing the entire building project, including sourcing materials and coordinating tradespeople. Many properties in Seattle, WA, are built on hilly and challenging terrain, and adding a secondary story may require additional labor to accommodate structural challenges and weather disruptions.

Cost of Living

The cost of living in Seattle, WA, is 45% higher than the national average, and home builder pricing reflects this difference. The U.S. Bureau of Labor Statistics (BLS) also shows that wages and salaries for workers in the city increased by 3.5% over one year.

Taxes

Sales taxes in Seattle, WA, apply to the price of materials and labor required for building a second story. With a 6.5% state and about 4% local sales tax rate, you can expect to pay an additional 10.5% on top of your total project costs.

Since a home addition will also likely increase your home’s value, you may have a higher property tax bill after your next assessment. The residential property tax rate in Seattle, WA, is about $10 per $1,000 of assessed value.

Building Permits

You’ll need to make sure you pull the proper building permits for your second-story addition. Your building contractor typically handles this, but the cost of a building permit from the Seattle Department of Construction & Inspections for a project valued at $200,000 is approximately $5,400. These fees vary according to the size and complexity of your project, the value of the work, add-on permits required, inspections, and other factors.

If you come up against strict laws in your area and your permit is denied, keep in mind that you may also need to pay for legal assistance to understand them. Historic homes, homeowner associations, and areas with strict air rights can be complex to understand without a legally trained eye.

Additional Pros to Consider Hiring

Adding a second story to a house is a big job, and general contractors may or may not outsource parts of the project. For example, structural engineers provide important expertise to ensure compliance and safety, while other contractors extend essential home systems into the new story. These are the experts you may hire and the rates you can expect in Seattle, WA:

• Structural engineer: $130–$150 per hour

• Interior designer: $100–$500 per hour

• Plumber: $45–$200 per hour

• HVAC technician: $90–$160 per hour

• Electrician: $60–$120 per hour

Does Adding a Second Story Increase Home Value?

Adding a second story to a home in Seattle, WA, can increase home value, offering a return on investment (ROI) of 20% to 50% on remodeling costs. Returns are often strongest for properties that expand livable space in high-demand neighborhoods, particularly for additional bedrooms or in cases of smaller lot sizes. High-end finishes can increase the total investment but appeal more to buyers if the design and amenities are consistent with the neighborhood.

How Angi Gets Its Local Cost Data 

To help homeowners plan their next project, Angi provides readers with carefully researched cost data and upholds strict editorial standards. We start with national average project costs, which we collect by analyzing competitor information, retailer material costs, and input from professional contractors. We then apply local price index data to calculate location-specific estimates that reflect what homeowners typically pay in their local area. To do that, we use data from the U.S. Bureau of Economic Analysis (BEA), including its Regional Price Parities (RPPs), which measure price differences across cities. This helps us account for differences in labor, materials, and overall cost of living, so estimates in higher- or lower-cost areas better reflect real-world local pricing.

Every estimate undergoes a thorough editorial review to verify accuracy, consistency, and alignment with observed market conditions.

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.