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Home Addition Cost in St. Louis [2025 Data]
Normal Range: $23,553 - $72,540
A home addition costs an average of $48,046 in St. Louis, Missouri. Depending on the location, size, type, and materials, most homeowners spend between $23,553 and $72,540.
How we get this data
Ursula Page / Adobe Stock Photography
Ursula Page / Adobe Stock Photography
Highlights
Building an addition on your St. Louis home can allow you to stay in your home as your needs grow and increase your home’s value.
Adding a bathroom or bedroom will have the highest return on investment (ROI) in St. Louis.
Home addition costs depend on the size and type of addition, material costs, labor costs, and more.
You’ll need a permit from the St. Louis City Building Division to build a home addition.
Building an addition is a great way to add valuable square footage if you’re outgrowing your St. Louis home but aren’t ready to sell. The cost to build a home addition in St. Louis averages about $48,046, with most homeowners paying between $23,553 and $72,540. We break down the factors that affect how much you’ll pay for a home addition so you can budget accurately for this major project.
Home Addition Cost Factors
The cost of adding on to your St. Louis, Missouri, home depends on multiple factors, including the size and type of the addition, how much site prep is required, permit costs, labor costs, and more. Take a look at some of the things that contribute to the cost of a home addition.
Size
Home additions cost between $80 and $200 per square foot if you’re building out and between $300 and $500 per square foot if you’re building up. The cost to add a 10x10 room to a house costs an average of $12,500 if you build out with a bump-out addition and $40,000 if you build up.
Price Notice
Remember that if you add square footage to your home, the cost of your homeowners insurance will increase accordingly. Before you embark on this project, speak to your insurance company about expected costs.
Where in those ranges your total falls also depends on the complexity of the room and its finishes. For example, adding a bathroom will often cost more than a bedroom since it requires additional plumbing and electrical work. Size will also affect how long your home addition takes, which may add to labor costs for the project.
| Project Size (Sq. Ft.) | Bump-Out Build | Second Story Build |
|---|---|---|
| 60 | $4,500–$11,275 | $16,900–$28,200 |
| 80 | $6,000–$15,050 | $22,550–$37,600 |
| 100 | $7,525–$18,800 | $28,200–$47,000 |
| 150 | $11,275–$28,200 | $42,300–$70,500 |
| 200 | $15,050–$37,600 | $56,400–$94,000 |
| 300 | $22,550–$56,400 | $84,600–$141,000 |
| 400 | $30,075–$75,200 | $112,800–$188,000 |
Materials
As you can imagine, it takes many kinds of building materials to complete a custom home addition. Material prices vary widely, so your price could push closer to $72,500 if you choose luxury or high-end materials at each step of the way.
| Framing Material | Average Cost per Sq. Ft. | Pros | Cons |
|---|---|---|---|
| Wood | $1–$5 | Cost-effective, easy to install | Fire risk, prone to pests and moisture problems |
| Steel | $2–$4 | Durable, fire-resistant | Complex installation, limits roof design |
| Insulation Material | Average Cost per Sq. Ft. | Pros | Cons |
|---|---|---|---|
| Blown-in | $0.50–$2.30 | Low-cost, fast installation | Prone to water damage, less durable |
| Fiberglass | $0.30–$1.50 | Fire-resistant, cost-effective | Lower R-value, easily damaged |
| Spray foam | $1.50–$4.90 | High R-value, resists pests and moisture | Higher cost, more flammable |
| Rockwool | $1.10–$3.10 | Durable, high R-value | Loose fibers can be a health risk, higher cost |
| Roofing Material | Average Cost per Sq. Ft. | Pros | Cons |
|---|---|---|---|
| Asphalt shingles | $1–$1.20 | Affordable, easy to install | Prone to granule loss, shorter lifespan |
| Metal | $5–$16 | Long lifespan, low-maintenance | Higher cost, difficult to repair |
| Slate | $10–$30 | Longest lifespan, high-end aesthetics | Very heavy, difficult to install/repair |
| Synthetic | $5–$12 | Durable, lightweight | Variable quality, may look engineered |
| Flooring Materia | Average Cost per Sq. Ft. | Pros | Cons |
|---|---|---|---|
| Hardwood | $6–$12 | Long-lasting, many available options | Higher cost, prone to dents and scratches |
| Laminate | $1.30–$6 | Budget-friendly, easy to install | Difficult to repair, prone to water damage |
| Tile | $5–$40 | Variety of options, easy to clean | More expensive, complex installation |
| Carpet | $3.50–$11 | Retains warmth, soft to walk on | Difficult to keep clean absorbs odors |
| Siding Material | Average Cost per Sq. Ft. | Pros | Cons |
|---|---|---|---|
| Vinyl | $3–$12 | Budget-friendly, easy to install | Shorter lifespan, prone to impact damage |
| Fiber cement | $5–$14 | Extremely durable, long lifespan | Higher cost, difficult to repair |
| Wood | $2–$6 | Eco-friendly, wide range of styles | Prone to rot and pest damage, high-maintenance |
Type
The cost to add on a room varies based on the type and size of the room you’re building. Rooms like kitchens and bathrooms require plumbing work that a bedroom doesn’t, while an unfinished attic home addition may not require electrical or HVAC work that a bedroom needs.
The cost per square foot for your home addition will vary based on utilities and the finishes required for how you plan on using the extra square footage. Here are some standard types of home additions and how much you can expect to pay.
| Room Type | Average Cost Range |
|---|---|
| Attic | $37,600–$43,250 |
| Bathroom | $32,900–$37,825 |
| Bedroom | $58,750–$67,550 |
| Dining room | $28,200–$32.425 |
| Kitchen | $51,700–$59,450 |
| Laundry room | $7,525–$8,650 |
| Living room | $28,200–$32,425 |
| Mudroom | $11,275–$12,975 |
| Sunroom | $44,175–$50,750 |
| Detached garage | $24,800–$28,575 |
| In-law suite | $77,775–$89,500 |
| Second story | $164,500–$188,950 |
Site Prep
On average, site prep for a home addition costs between $1,500 and $5,000. You may not need any site prep in some cases, while other home addition projects may require grading land, demolishing concrete patios, removing trees, and other work that can add to your total.
Permits
When building an addition, you’ll need a permit from the St. Louis City Building Division. Although your general contractor or home builder will normally pull all necessary permits, it’s the homeowner’s responsibility to ensure all work is properly permitted, so confirm with your builder and the city to ensure your addition is fully permitted.
Building permit fees vary based on the total cost of your project. Depending on the size and cost of your addition, expect to pay between $45 and $2,000 for permits.
Home Addition Pro Costs
Hiring a general contractor or homebuilder in St. Louis, MO, will cost an average of 10% to 20% of the total project price in labor costs. An experienced builder can coordinate all the necessary professionals, keep your project on schedule and budget, answer your home addition questions, and manage the project from beginning to end.
Additional Pros to Consider Hiring
Building an addition can require various professionals, including electricians, HVAC techs, plumbers, roofers, and structural engineers. Here are some additional pros you may need to hire when building an addition.
Interior painter cost: $2–$6 per sq. ft.
Roofer cost: $4–$11 per sq. ft.
Electrician cost: $50–$100 per hour
HVAC technician cost: $100–$250 per hour
Plumber cost: $45–$200 per hour
Carpenter cost: $75–$125 per hour
Structural engineer cost: $200–$1,500
Landscaper cost: $1,200–$6,200
Does a Home Addition Increase Property Value?
Home additions can add value to your home, offering a return on investment (ROI) of 20% to 50% or more. ROI depends on the type of addition, the materials and finishes used, and the overall project cost. In St. Louis, adding a bathroom or additional bedroom can have the most significant impact on your home’s value, with an ROI of 50% to 75% or more.
How Angi Gets Its Cost Data
Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We survey real Angi customers about their project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects.
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.
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