Room additions cost$16,989 - $25,396

National average fixed price

Most common low price:$16,989
Most common high price:$25,396

How much does it cost to add a room to a home?

By Thumbtack Staff

Last updated Mon, Oct 20

The national average cost of adding a room to a home ranges from around $16,989-$25,396, and most people pay around $18,508, according to Thumbtack data. However, some additions can cost as much as $67,421-$81,361. The total cost can vary significantly based on the size of the room, plumbing requirements, and more.

National average cost	$18,508
Low-end average cost	$16,989
High-end average cost	$25,396

A home addition can add an entire level to a home, expand the master bedroom or bump out a cramped bathroom. Architects and general contractors provide professional help to get the job done the way you want it—and to meet code requirements. From architectural drawings, general contractors build new home additions from the ground up—leveling land as needed, pouring a cement foundation, framing out the structure, finishing the walls and floors, and adding the finishing touches such as new fixtures or appliances. Home addition projects can take six weeks to complete or more than six months, depending on how many square feet and how complex the job is. Numerous factors affect overall costs.

Price per square foot
Architectural plans
Region
Finishes

Price per square foot

Most general contractors estimate jobs based on a price per square foot. Finishes are a key factor in home additions, just as in home renovations. Contractors can provide a more realistic cost per square foot if they can review architectural plans and have as much detail about finishes as is possible.

Variance in soil can also affect home addition costs, says Mini Spalter with YYB Construction in Milpitas, California. If the construction company must dig down six feet instead of four feet for foundation work or if more rugged drilling machinery is required (either for clay or rock), the cost per square foot increases. Typically the cost per square foot includes laying any necessary foundation, framing the structure, any plumbing and electrical work, drywall, painting, and flooring.

Here are a couple addition projects from YYB Construction, with examples of price per square foot in one of the country’s more expensive places to build:

Basic addition: $250–$270 per square foot in San Jose, California
Kitchen and bathroom additions: $280–$300 per square foot

800-square-foot, second-floor addition in San Francisco

Estimated cost: $290 per square foot = $232,000
This price includes interior and exterior paint and everything except finishing materials (the owner purchased upgraded flooring and bathroom fixtures).
Work included one to two weeks digging and laying cement and waiting to pass foundation inspection.
Once the inspection was passed, contractors framed the building, added windows and roofing. Drywall was applied inside and stucco outside.
Finishing included paint, floor installation and bathroom tiles.

1,250-square-foot, first-floor expansion and second-floor addition in San Francisco

Estimated cost: $300 per square foot = $375,000
The homeowner wanted special structural reinforcement because a third floor will be added on at a later date.
The foundation was difficult to work on, which increased overall project costs.

Architectural plans

Larger home additions often require architectural plans. Architects charge either a flat fee, an hourly rate or a percentage of the total project cost. Here is a sample home addition budget from Archwork in Somis, California, reflecting how the architect fee is a percentage of the total construction costs:

1,000-square-foot addition @ $200 per square foot = $200,000

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Region

The cost per square foot of adding rooms onto a home varies greatly depending on geographic region. The regional cost of labor and the area cost of doing business affects total costs. Places with extremely high real estate costs and higher costs of living, such as the San Francisco Bay Area, typically see higher prices per square foot for home addition construction projects than areas with a lower cost of living and more affordable labor.

Finishes

Finishes include all those lovely touches that transform a new home addition from an empty room with painted walls to one with light fixtures, double-pane windows, brass door knobs and white oak floors. The choice of finishes significantly affects the total project costs. For the cost of a 2,500-square-foot addition, the finishes alone can double or quadruple a project budget, says architect Quentin Parker of Archwork. For instance, in a new kitchen addition, choosing high-end kitchen cabinetry, appliances and other finish materials can boost the project cost by $20,000–$200,000, depending on how luxurious the homeowner goes.

How do we know these prices?

Millions of people ask Thumbtack for help with their projects every year. We track the estimates they get from local professionals, conduct our own research and then we share those prices with you. The prices reflected in the article above are for informational purposes only and are subject to change at any time. Contact a professional near you to receive a personalized cost estimate for your project.

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