Room Addition Cost (Design Guide)

Building a room addition is a great way to get yourself some additional living space and add additional resale value to your home. A room addition is basically an extra structure that you build onto your existing home.

New room addition in home

Depending on the type you want to add, building a room addition may be less expensive and less stressful than moving into a new house. In addition, with a brand new room addition, you can get a space that fits your exact needs and specifications.[toc]

How to Calculate Room Addition Cost

Room addition

When you are planning a room addition, you need to be aware of the following things that can affect the price. The main price factors will be labor and material, but you also need to be aware of the cost of permits. The price of permits can vary according to where you are located.

Another big thing to think about is the type of materials that you will be using, this can increase or decrease the total price. There are also some ways that you can save on labor prices. While DIY might cost less, hiring certain experts such as plumbers and electricians will keep you from making costly mistakes.

Room Addon Cost Per Square Foot

In the United States, the national average for the cost of an addition will be around $80-200 per square foot. This is for a ground-floor addition.

If you are looking to build a second-story addition the price will increase as these are more difficult and complex to build. A second-story room addition will range from $100 to $300 a square foot.

Room Extension Cost Breakdown

Room addition with vaulted ceilingAddition with vaulted ceiling design

The first step you need to take in building your room addition is to secure the necessary building permits. Depending on where you are, permits could cost you $100- 300 each.

The next step would be to prepare the building site. This could include excavation and demolition. This stage should cost about $1,500 to 3,000.

Next would be laying the foundation, this should cost about $4-8 for every square foot.

Here are the rest of the general elements of a room addition and their respective prices. Again, remember that the price can either increase or decrease depending on the material used and whether you DIY or hire an expert:

• Roofing: $7-10 per square foot
• Siding – $8 per square foot
• Insulation – $2-3 per square foot
• Drywall – $2 per square foot
• Flooring – $2-4 per square foot
• Windows – $400-800 per square foot
• Crown molding – $7 -16 per linear foot
• Plumbing – $450 – $1,800 per fixture
• Electrical – $2 to 4 per square foot
• HVAC & Ducting – $800 to 1,600
• Landscaping – $500 – $2,500
• Clean up – $500- $1,000

If you are building a small basic space, you might want to skip on hiring an architect. But if you’re planning a big add-on with a lot of fixtures and features, you should consider having an architect draw up your building plans. This could cost you about $2,000- $5,000.

Material Prices For Room Enlargement

As we mentioned before, the type of material will affect the overall price. One tip we can give you to save on the price of building materials is to consider the dimensions of the building materials. Every bit of material that you need to add or cut will affect the price.

For example, most two-by-fours come in lengths of 8 feet; this means that you can maximize the use of the material by building rooms with dimensions in multiples of 8. Doing this saves you money because you don’t have to cut or add material.

Labor Cost

Hiring a contractor will up your room’s renovation pricing. Labor and contractor prices will come to around 30-50 percent of your total budget for your addition depending on your location.

Doing things yourself, or even partially yourself could save you some money. For example, if you do your own demolition you could save $500 in labor prices. However, some of the more complex operations, like installing plumbing or electrical wiring might be better off left to the professionals.

Always get several estimates before beginning any construction work and have a timeline and payment schedule prepared so you get the work completed efficiently.

Average Cost of Room Expansion

Room addition to homeUltimately, the average cost of a room addition depends on the type and size of the addition.


The average price to add a 12 foot by 12 foot extension to your home will come to around $11,520 – $28,800

12×12 DIY

If you decide to do it yourself, you should subtract the labor price from your budget. If we say that labor costs are 30% of your budget, DIY-ing should bring the total to around $8,064 – $20,160.


If you want to add a 20 foot by 20 foot square feet expansion to your home, be prepared to spend from around $32,000 to $80,000.

20×20 DIY

If you decide to DIY, subtract the labor from your total budget. If we place the labor costs at 30% of the budget, DIY-ing should be around $22,400 – $56,000

Bathroom Add-On Cost

Remodeling part of your existing structure to become a bathroom can add a minimum of $5000 depending on the amount of labor involved. To add a bathroom addition to your home will cost at least $50,000.

The U.S average for a bathroom add-on is $75.000. The price will vary substantially based on the state you reside in and its permitting process as well as local labor and the materials you choose. To create your own plan there is bathroom remodel software to help.

Family Room Cost

The price of a family or living room addition will depend on the size of the floorplan you want. The average size for a living room is about 18 by 12 feet and will be priced around $17,300 to $43,200.

The fixtures that you want will also increase the price so keep that in mind when thinking about cabinets, lights, and even molding. For living room remodel ideas visit this page.

Laundry Cost

Laundry room addition

Building the laundry area extension itself will only cost about $2,000 to $10,000 depending on the size and the material that you use.

What can really up the price would be the fixtures such as plumbing, appliances, and even storage space. With that in mind, the average price to add a laundry area should be $5000.

Mudroom Extension Cost

The mudroom addition cost runs between $100 to $200 per square foot if you are building in an existing interior space.

If you’re building from the ground up the price will be much higher and can be anywhere from $100 to $500 per square foot depending on local building codes, materials, and labor.

Mobile Home Build-Out Cost

Take note that, when you’re building a mobile home addition, the new extension cannot be attached to the mobile home. The mobile home might not be able to support the weight of an addition.

These are the most common types of mobile home additions and their average price:

• Barn or shed – $1,700 – $5,000
• Carport (metal) – $2,150 – $4,800
• Deck – $4,000 – $11,000
• Porch – $4,600 – $10,500
• Detached garage – $4,600 – $10.500

Prefab Room Add-On Cost

Modern modular home addition

A prefab or modular home is basically a structure that you can erect out of parts or pieces that are prebuilt. You buy a modular home and the parts are shipped to you and you or your contractor just has to put it together in your property.

You can also get prefab dwelling add-ons. The most common types of modular extensions and their average costs are as follows:

• Shed – $3,000
• Deck – $7,500
• Basement – $18,000 to $30,000
• Two-car garage: $27,000

Cost of Three Season Room

If you want to add a three-season room to your home, it will be priced around $9,000 to $40,000. Most of the price will come from material prices for which you should budget around $5,000 to $30,000.

Labor costs for a three-season room addition will come to around $9,000 – $40,000.

To help visualize your plans you can use one of the many home design software programs available.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *