How Much Does It Cost to Build a Bump-Out?

Laura Hennigan
Written by Laura Hennigan
Updated January 24, 2022
Modern renovated kitchen and dining area
Photo: Iriana Shiyan / Adobe Stock

The cost to build a bump-out micro addition is $4,000 to $30,000

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If you’re ready to add some extra space, the cost of a bump-out in 2021 ranges from $4,000 to $30,000. The room you’re expanding influences the final price, including the cost of materials and the desired size of the bump-out.

What Is a Bump-Out?

A bump-out is a small addition to an existing room in your home, such as the kitchen or a bedroom. It’s not nearly as expensive or time-consuming as a full room addition and is an excellent option for homeowners looking to create just a little extra space. Bump-outs, also known as “micro additions,” come in as small as two feet or extend up to 10–15 feet from the house.

Because you’re expanding an existing room, the project doesn’t require additional heating and cooling elements, significantly cutting costs. 

During the bump-out construction, a pro will install new floor joists alongside the existing joists. This provides the necessary bottom support, as the bump-out will not have an underlying foundation. 

Small bump-outs are cantilevered off the existing foundation, so the additional weight is held by your home’s existing floor joists. Bigger bump-outs typically require additional support posts. The larger the floor joists, the larger your bump-out can be.

How Much Does It Cost on Average to Build a Bump-Out per Square Foot?

Bump-Out SizeCost to Build
2-foot (cantilevered)$5,000
2-by-10-foot $17,000
4-by-10-foot $30,000

How Much Does It Cost to Build a Bump-Out Near You?

Here are examples of the average cost of building a bump-out in various regions of the United States:

CityAverage Cost
Boston, MA$6,000–$35,000
Chapel Hill, NC$4,500–$29,000
Chicago, IL$5,500–$36,000
Denver, CO$6,000–$30,000
Detroit, MI$3,500–$30,000
Orlando, FL$4,500–$31,000
Phoenix, AZ$5,000–$28,000

What Type of a Bump-Out Can I Get on My Budget?

Professional inspecting home for bump out
Photo: Khwanchai / Adobe Stock

If you’re only trying to create a small amount of extra space, like for a bay window and seat, a shallow bump-out of two to three feet will be plenty. On the other hand, if you want to reconfigure part of your kitchen to create more storage, a larger bump-out of 10-15 feet may be necessary. 

Here are estimates of how large of a bump-out you can get for your budget:


Bump out two feet along one kitchen wall, allowing for an island or large picture window.


Install a small library nook or additional playroom storage with a 2-by-10-foot bump-out.


A 3-by-10-foot bump-out will provide enough room for a larger entryway or front porch expansion.

$30,000 or More

By creating a compact 4-by-10-foot bump-out, you can open up enough space for a laundry or mudroom.

Bump-Out Average Cost Breakdown


All home additions, no matter how small, require a building permit, which costs between $400 and $1,500. Even if you only create a two-foot bump-out, it’s important to acquire a permit before any work begins. Additions made without the proper permit run the risk of having home insurance claims denied in the future.


Even though bump-out construction isn’t as intensive as a full room addition, we recommend working with a professional. General contractors rarely charge an hourly rate, instead usually quoting 10% to 20% of your project’s total cost. While some homeowners may feel confident enough to try and tackle a bump-out project themselves, it’s important to remember you must complete all tasks. This includes opening a wall, pulling up flooring, attaching joists, and possibly lowering the ceiling. In virtually all cases, you should hire a professional.


Window installation costs between $3,500 and $15,000, depending on the size and style you choose. Large picture or bay windows, along with skylights, will land you on the higher end of prices.


Depending on the size and location of your bump-out, you may need to add in additional wiring for lights or a ceiling fan. Expect to pay between $50 and $100 per hour for a licensed electrician to perform the work.

Interior Bump-Out Finishing

You’ll likely want to continue the existing wall and floor styles into the micro expansion. Expect to spend $2 to $6 per square foot on painting and $3 to $22 per square foot on flooring.

Exterior Bump-Out Finishing

Once completed, a bump-out will likely need siding, which costs between $3 and $11 per square foot. If you need to extend your roof to cover the addition, the typical cost is $50 to $85 per running foot.

FAQs About Bump-Outs

What type of bump-out can I build?

Nearly any room in your house could be a candidate for a micro-addition, making the possibilities truly endless. Upgrading the kitchen, bathroom, or bedroom all provide a high return on investment, in addition to delivering a significant design impact with a small footprint.

In the kitchen

  • Expand storage space with an expanded pantry

  • Add countertop or island prep areas

  • Build a breakfast nook

In the bathroom

  • Install a soaking or whirlpool tub

  • Upgrade your sink and vanity

  • Expand a linen closet

In a bedroom

  • Expand a walk-in closet

  • Add a gas fireplace with surround

  • Create a sitting area with a bay window


  • Turn your back patio into a sunroom

  • Transform a front porch into a mudroom

  • Add an outdoor kitchen extension

Are bump-outs an easier renovation?

Bump-outs create more space nearly anywhere in your home, including rooms on the second story. Because they are small expansions, bump-outs don’t connect to the foundation, making these micro-additions faster, easier, and cheaper than a larger renovation project. 

In addition, bump-outs allow homeowners to implement some of the top house-selling features, including expanded walk-in closets, renovated bathrooms, and larger windows.

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