How much does a home addition cost?
Ashburn, VA

How much does a home addition cost?

Ashburn, VA

How much does a home addition cost?

$125 – $250average cost per square foot
$50,000 – $100,000cost for 20' x 20' room addition

Get free estimates for your project or view our cost guide below:

$125 – $250 average cost per square foot

$50,000 – $100,000 cost for 20' x 20' room addition

Get free estimates for your project or view our cost guide below:
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Tamatha Hazen
Written by
Tamatha Hazen
Edited by
Tara Farmer
Fact-checked by
Kristen Cramer

Home addition cost per square foot

A home addition costs $125 to $250 per square foot total on average, depending on the type and features. A 20x20 room addition costs $50,000 to $100,000, including labor and materials. The cost of a house addition depends on its location, size, complexity, and the quality of the finishes chosen.

Home addition price per square foot
Room addition size Square footage Average cost
10x10 100 SF $12,500 – $25,000
10x20 200 SF $25,000 – $50,000
12x12 144 SF $18,000 – $36,000
20x20 400 SF $50,000 – $100,000
20x30 600 SF $75,000 – $150,000
15x40 600 SF $75,000 – $150,000
20x40 800 SF $100,000 – $200,000
25x40 1,000 SF $125,000 – $250,000

New foundation and first floor of home addition framed and covered with OSB
New foundation and first floor of home addition framed and covered with OSB
Get free estimates from home addition contractors near you.

House extension cost by type

When people think of a home addition, they often picture a room extension off the back of the house. However, a home addition can also involve converting an existing garage or attic space, or even adding a second story. The following table details the common addition types.

House extension cost calculator
Addition type Average cost per square foot
Room addition $125 – $250
Bump-out room extension $85 – $200
ADU addition $100 – $300
Attic Conversion $50 – $150
Basement conversion $50 – $100
Garage conversion $50 – $200
Second-story addition $200 – $500+
Sunroom addition $100 – $350

Room addition

The average cost per square foot for a room addition is $125 to $250 when adding a completely new room to your home instead of extending an existing room. Factors such as the type of room and the need for additional plumbing, fixtures, or cabinetry affect the final price. 

The common steps for a room addition include:

  • Planning: Work with an architect or designer to create detailed plans that comply with local building codes.

  • Permitting: Check with your local building department for permit requirements before you start any construction work.

  • Foundation & framing: Excavate and pour the foundation or install a concrete slab. Then, frame the new room with walls, floors, and a roof.

  • Utilities & systems: Extend electrical wiring and outlets, install lighting fixtures, and add HVAC systems as needed. If the addition includes a bath or kitchen, extend plumbing to the space.

  • Exterior finishes: Install windows, doors, siding, insulation, and roofing to match the existing structure.

  • Interior finishes: Complete drywall, finishing, painting, flooring, and trim. Add lighting outlets, switches, and fixtures.

  • Inspections: Ensure building code compliance by scheduling and passing inspections throughout construction.

Room extension cost

A bump-out addition costs $85 to $200 per square foot to extend an existing room and make it larger. Cantilevering a small bump-out from the existing foundation with no footings or foundation walls can save on costs.

ADU addition

An accessory dwelling unit (ADU) addition costs $100 to $300 for an in-law suite designed for full-time living. This attached, detached, or converted secondary living space includes a bedroom, kitchen, and bathroom.

Attic conversion

Converting an existing attic to a finished living space costs $50 to $150 per square foot. Converting the attic to a new primary suite with an en suite bathroom costs more than converting it to a guest bedroom or flex space.

Basement conversion

The cost of converting an unfinished basement is $30 to $50 per square foot to finish the space or $50 to $100 per square foot on average to create a fully livable home addition. Costs are higher if you need to excavate to dig and build an entire basement addition. 

Garage conversion

Converting a garage costs $50 to $200 per square foot to turn the garage into a functional home addition that serves as a secondary dwelling unit. Converting the garage into a flex space without plumbing is cheaper and faster.

Second-story addition

A second-story addition costs $200 to $500 per square foot, including finishing the space. This addition is costly due to the structural changes needed to support the increased weight on the home. Builders must modify the foundation, walls, and roof. Also, adding stairs may require higher engineer or architect fees.

Sunroom addition

A sunroom addition costs $100 to $350 per square foot on average, depending on if it's a 3-or 4-season room. An all-season or 4-season sunroom addition has insulation, electricity, and an HVAC system, while a 3-season sunroom addition is enclosed with glass but lacks insulation and an HVAC system.

Sun room addition with large windows and bright lighting
Sun room addition with large windows and bright lighting

Cost to add a room to a house

The cost to add a room to a house depends on the room type, size, and features of the space. A bedroom, flex, or family room costs less to build than a primary suite with multiple spaces and plumbing features.

Home addition cost by room
Room Size (square feet) Average cost
per square foot
Average total cost
Bathroom 40 – 50 $175 – $225 $7,000 – $11,000
Bedroom 120 – 140 $125 – $175 $15,000 – $25,000
Family room / Flex room 200 – 225 $125 – $175 $25,000 – $40,000
Kitchen 100 – 200 $200 – $250 $20,000 – $50,000
Primary suite 300 – 600 $150 – $225 $45,000 – $135,000
Sunroom 150 – 300 $100 – $350 $15,000 – $105,000

Some common room addition sizes and costs include:

  • A 10x10 room addition costs $12,500 to $25,000. This 100 square foot space is adequate for a child’s bedroom, a home office, a craft room, or a storage area.

  • A 12x12 room addition costs $18,000 to $36,000. This 144 square foot space provides a roomier bedroom adequate for guests.

  • A 20x20 room addition costs $50,000 to $100,000. The cost of a 400 square foot addition is much higher than adding a small bedroom, but is more than adequate for a family room, living room, or dining area.

Lake house sunroom home addition
Lake house sunroom home addition

Cost to add a bedroom to a house

The cost to add a bedroom ranges from $15,000 to $25,000. Factors that affect construction costs include the size of the bedroom, if walls need to be moved or added, if plumbing must be relocated, and your selections for finishes like flooring, lighting, and trim.

Adding a primary suite costs $45,000 to $135,000 since the addition includes not only a large bedroom space but an additional bathroom as well.

Home addition cost estimator

The cost of a home addition depends on many factors, including:

  • Addition size: Building a larger addition takes longer and requires more materials, increasing costs.

  • Complexity: The more complex the addition, the more you will spend on architectural or engineering fees and construction labor.

  • Zoning: Most areas regulate home additions and require permitting fees, impact fees, or other costs to meet local requirements.

  • Features: The more features you include, the higher your building costs. Most additions require electricity and HVAC, while others also require plumbing, which adds to the costs.

  • Interior finishes: High-end fixtures and finishes will increase the cost of the home addition. Granite counters, stainless steel appliances, and hardwood floors are common high-cost upgrades.

  • Permits & construction delays: The permitting process, bad weather, or material shortages can cause construction delays, resulting in higher costs.

Planning and site prep

Before you can build a home addition, you’ll most likely need to hire an architect or engineer to help design and plan your addition. If you are extending the home’s foundation, you will also need to prepare the site for construction. The following table details common costs related to planning and site prep.

Home addition planning and site prep costs
Factor Average cost Details
House plans $1,200 – $5,000 New addition plans drafted by an engineer or architect
Land survey $400 – $1,800 Marks the foundations, utilities, boundaries, and topography for the addition
Home site excavation $1,500 – $5,000 Includes digging a foundation pad for the new extension
Grading and leveling $1,000 – $5,000 Includes making the yard level before adding an extension to the existing foundation
Foundation $2,400 – $10,500 Includes costs for pouring a concrete slab foundation for the addition
Building permits $500 – $2,000 Depends on local permitting requirements and fees

Get free estimates from home addition contractors near you.
Home addition contractors raising built wall for room addition
Home addition contractors raising built wall for room addition

Home addition FAQs

What is a home addition?

A home addition is the expansion of a residential property by adding new living space or rooms. The addition can be a bump-out room extension, a new room or second story, or a converted garage, attic, or basement. 

Does a home addition increase property value?

Yes, any home addition that increases the square footage of your home should increase the property value. Depending on the type of addition, you can expect to recoup about 60% to 80% of the cost of the addition when you sell the home.

How can I finance a home addition?

You can finance a home addition in several ways, including:

  • Home equity loans: This bank loan allows you to borrow a lump sum of money using your home's equity as collateral.

  • Home equity line of credit (HELOC): Rather than borrowing a lump sum, this revolving credit line allows you to borrow against the equity in your home as needed.

  • Cash-out refinances: Refinancing your mortgage involves taking out a new loan for more than your current mortgage balance. The lender pays the difference in cash, which can pay for home improvements.

  • Personal loans: Unsecured personal loans do not require collateral but have higher interest rates than secured loans. The loan approval and interest rate depend upon your creditworthiness.

  • Credit cards: For smaller home additions, consider using a low-interest-rate credit card and pay it off quickly.

How can I save on a home addition?

To save on the cost of a home addition, consider the following suggestions:

  • Choose a simple plan with limited features to keep costs down.

  • Build the smallest addition that meets your needs and local regulations.

  • Try to convert an existing space like a basement, garage, or attic, which costs less than building an entirely new space.

  • Do simple tasks like painting and interior finishing yourself to save on professional labor.

  • Choose cost-effective building materials and finishes when possible.

Getting estimates from home addition contractors

If you are considering a home addition, first check to see what type of addition your city zoning regulations allow. Then, follow these suggestions to get the best home addition contractor near you.

  • Compare several estimates with the same addition size, materials, and features.

  • Check out recent reviews for home addition builders on HomeGuide and Google.

  • Pick a contractor experienced in the specific type of home addition you want.

  • Ask to visit a job site to see their construction work in progress.

  • Request an itemized, written contract in case of disputes.

  • Ask your contractors about their preferred lenders for easier financing.

  • Avoid large upfront payments. Never pay in full or in cash.

Questions to ask a home addition builder

Ask these important questions to narrow down the list of contractors for your home addition project:

  • How many years have you been building home additions?

  • How many home additions did you complete within the last year?

  • Do you offer design help for creating a floor plan for the addition?

  • Do you have a list of references from past clients, along with their contact details?

  • Do you have a portfolio of your past home addition projects?

  • Do you have a recent home addition project I can visit to see the work quality?

  • Do you have the necessary licenses, insurance, and bonds?

  • What are my options for where to build an addition to my home?

  • How much will the home addition cost?

  • Are there any ways we can get the cost down?

  • How long will the home addition take?

  • Who will serve as my project coordinator?

  • Do you use your own crew, or do you subcontract the work?