Home Addition Cost Estimator | Cost To Add A Room

Average reported cost to build an addition is $35,000-60,000. Because house additions come in a wide range of shapes and sizes, the construction costs vary greatly.

While expensive, building a home addition is a highly rewarding undertaking. After all, you will have the desired extra space, without having to buy a larger house.

Here is an updated list of popular house additions and their costs to help you plan your budget.

How much does a new addition cost?

Home Addition Costs

The price for a large house addition that includes a kitchen or bathroom is comparable to building a small home. On average, addition cost per square foot is $125-400. Obviously, the addition’s size and location will be the primary cost drivers, but the following factors may jack up the final price as well:

– complexity of architectural design
– quality of building materials and finishes
– permits and inspections
– unexpected plumbing, HVAC or electric issues

Here is what you can expect to pay to add on different types of rooms. This estimate includes: new foundation, roof, siding, proper wall insulation, new windows, flooring, electric, HVAC and finishing work.

Typical bathroom addition cost: $25,000-40,000 for a 5×8 room with a tub or shower enclosure.

  • A spa-like, master bathroom: as much as $80,000+
  • An average size kitchen without the luxury bells and whistles: $25,000-50,000
  • Upscale kitchen with custom cabinetry and high-end appliances: as high as $100,000+
  • 10×15 bedroom (without a bathroom): $20,000-35,000
  • Room addition cost (400 sq.ft.): $30,000-100,000
  • First floor addition with multiple rooms (800-1,500 sq.ft): $150,000 +
  • Second floor addition with multiple rooms (1,500 sq.ft.): $200,000-475,000
  • Sun room or three/four season room without heat (250 sq.ft.) $30,000-55,000

If you are planning a complex project, such as a two-floor addition, you will need to hire an architect and budget for his fees. These can be as much as 5-7% of the total cost. Some people save money by hiring a design-and build firm, that has a staff architect and includes the design fees into the final price.

Expect to spend $1,200-2,500+ on blueprints and $2,000-5,000+ on architectural design.

While these prices may seem extremely high and out of your budget, you can pay for the addition by getting a home equity loan. In fact, that is what the majority of homeowners do. Another financing option is to get a construction loan.

The key to setting a reasonable budget and sticking to it is to identify and manage all the anticipated remodel costs in the beginning stages of the project.

To be on the safe side and avoid running out of funds, its best to budget 15-20% of the total cost for unforeseen expenses.

House addition cost by room size

The larger the size of the space you are looking to build, the less you will be paying per square foot. Here are popular addition room sizes and their price estimates.

20 x 20 room addition costs $50,000-100,000

12 x 12 room addition costs $18,000 – 36,000

10 x 12 room addition costs $15,000 – 30,000

Overall, 20×20 room additions that include either a bathroom or a kitchen are most popular. This is because adding a small room does not provide much extra functionality or value to the home. Moreover, additions that have a bathroom are a lot more popular than bedroom or office additions, because it is always helpful to have an extra bathroom in the house.

Cost of adding a bathroom

Among all room addition types, a bathroom is the most desirable upgrade that also boasts one of the highest ROI’s. Because plumbing work is a necessary component of building a bathroom addition, the overall cost is higher, compared to adding a simple room. An average size bathroom addition (5×8) costs $25,000 – 40,000.

Overall, prices for a bathroom addition start at around $450-500 per square foot, compared to an average of $200 per sq.ft. for a regular room. A high-end luxury bathroom addition costs as much as $700-850 per square foot.

There are also increased labor costs in having to install all the bathroom fixtures, tile the floor/walls, put in cabinetry/shelving. Moreover, there is a very wide price range when it comes to bathroom fixtures, themselves. For example you can install a standard toilet by American Standard from Home Depot for $200, or a TOTO toilet for $1,500.

If heating your bathroom addition is a challenge as its too expensive to extend the main source of heat into the addition, consider installing a mini split heat pump and radiant heated flooring.

Curb appeal of a home addition

When designing a home addition, whether its its just a sun room or a two-storie master suite or an in-law apartment, its important to consider how the addition will look attached to the main home. The last thing you want is for the addition to seem like it was hastily tacked on to the house and now it sticks out like a sore thumb.

Ideally, an addition should look like an organic extension of the house, where the flow from the old space to the new feels very natural. This requires professional architectural planning and design. Its also important to carefully select your siding and roofing materials, so that they match and complement the siding and roof of your original home.

While you may not care what your addition looks like on the outside, this may become a stumbling block if you ever decide to sell your home. Prospective buyers will love the expanded foot print of your house, but they may have a major problem if the addition really looks out of place.

A new design trend that has been growing in popularity is to build a modern addition together with a classic architectural style home. Modern additions usually have flat roofs, oversized windows and make use of engineered wood or fiber cement siding materials.

Cost of a second story vs ground floor addition

Many homeowners who are looking to save money on the cost of an addition wonder if its cheaper to build up (add rooms to the second or third floor of the house) or to build out?

Before you consider the cost of these two addition types, you need to first find out your zoning laws and what you would actually be allowed to build. Ask your town inspector to come in and guide you. In some cases you may only have one option available to you, so that will spare you the headache of making a decision.

In terms of building costs, its considered to be overall cheaper to build up rather than out. This is because building a ground floor addition requires excavation and building a foundation, which dramatically increase your total cost.

However, when building up, you have to first make sure that the house structure can support the new addition. If it cannot and you have to reinforce it, the cost becomes similar or even higher compared to building a ground floor addition.

If you are trying hard to save money and don’t need a lot of extra space, consider bumping out, or building a shed dormer addition. This will not require you to change the foot print of your home, and can be done using the existing house and roof structure. Many small bathroom additions are built as shed dormers.

The cost of a large shed dormer that can fit a bathroom can be $25,000-30,000. This is significantly cheaper than building an addition.

However, aside from budget there are other factors that you need to consider, when deciding whether to build up or out:

1. Purpose of the addition

If you are looking to add a bedroom, an office or a bathroom, it is reasonable to do this on the second floor. However, if you are looking to expand the kitchen, or add an entertainment room, it makes sense to build these on the ground floor. Moreover, building an in law apartment is also often more convenient as a ground floor as opposed to a second floor addition.

For someone who is looking to add extra space, such as a guest room, office, play room, man cave, etc finishing your attic or basement may be the easiest and cheapest way to achieve this goal. No major, expensive construction required! You can remodel and finish your attic for $12,000-20,000, and get a very nice addition to your house space without breaking your bank.

2. Home value

Your addition should add to the value of your home, and the best way to do this is with increased functionality and convenience. As a rule of thumb ground floor additions are considered more convenient, as many people (especially older ones) don’t want to bother walking up and down the stairs. However, this can also be market specific, so its best to consult with your local realtor and get some hard data as to which types of house additions are more popular in your area.

3. Will you be sacrificing valuable backyard space?

Some homes don’t come with huge lots of land, and building a ground addition may mean that you will be left with a very small backyard. If this is an undesirable, as you use your backyard for kid’s play and to entertain guests, perhaps you have a portable pool, etc, it may make sense to build a second floor addition.

4. Convenience during the construction phase

If you plan on building a second story addition, you have to be ok with a prolonged disruption to your house routines as well as noise. You may also need to move out of your house for the duration of the construction. Plan ahead and see if this is feasible for your family.

Factors that drive up addition cost

Home Addition Cost Estimator

There are a number of factors that may significantly increase the total cost of an addition. For example, if you are adding a new bathroom or a kitchen, you will need to install an entirely new plumbing system. This will cost thousands of dollars. One way to save money on this is to connect to the existing plumbing system, if the addition design allows for it.

Another significant expenditure is hiring a mason to pour a level concrete floor, if you are planning to build a garage.

You should also budget at least $1,500-4,000+ extra to fix the landscaping around the new addition.

You will need to pull building permits for most of the construction and remodeling jobs. Each permit will be a few hundred dollars. Also, you may need to run special kinds of tests, such as soil testing, which may cost $1,000+

Keep in mind that if you do not hire a General Contractor to oversee the project and hire subcontractors, you will need to hire these pros yourself to complete specialized tasks. They may include a roofer, electrician, plumber, window installer, etc.

To get the best rates, be sure to get price quotes from 3-4 local pros.

Lastly, the quality of materials you select will also make a great difference in the final price. Choosing custom, brand name, or luxury building materials can significantly drive up construction costs. Here, you need to carefully consider your total budget and what you are planning to achieve.

Sometimes, going for more expensive materials is justified because of their improved longevity and durability, as opposed to spending a lot more money just to have an upscale look. For example installing a metal roof instead of asphalt shingles may cost $10,000-15,000 more, but will offer superior weather protection for the lifetime of your house.

ROI of a house addition

Because a house addition is such a major remodel that also costs tens of thousands of dollars, its important to consider your return on investment before you jump into it.

In general a room addition, whether second floor or attached has an ROI of about 40-50% Large room additions that have a bathroom have a much higher ROI of about 60%.

Homeowners can get the best returns by building a multi room addition with a bathroom that has a separate entrance, such as an in-law apartment or a suite. You can expect the ROI to be about 85-95%

Keep in mind that high-end and luxury remodels do not have a high return on investment. So if you want to splurge for your personal enjoyment and install expensive finishes, fixtures and accessories, go for it! However, don’t expect to get more than 20-25% of your investment if you put your house up for sale.

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About Leo B

Leo has been a contractor since 2003, specializing in: roofing, siding, general contracting (GC) and residential remodeling. Leo is also a Certified HVAC, Oil & Gas Heating Technician/Installer. In addition to roofing and remodeling, Leo is passionate about Solar, green building and energy conservation, so a lot of my time and energy goes to installing energy efficient heating and cooling systems.

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6 comments on “Home Addition Cost Estimator | Cost To Add A Room

    1. Leo B Post author


      Try to get a quote for local builders / contractors, to see the “non Central Park” addition costs. You must really not understand the amount of materials and labor that goes into building an addition, and on top of that contractor needs to make profit, and cover overheads (insurance, taxes, advertising, bookkeeping, office, etc).

      If addition is on the ground, you need to pay excavators, concrete pourers, and then a standard framer, electrician, roofer, plasterer, flooring and painters, etc. Also include architects/engineers, building permits… its not as simple as building a shed from 2x4s and OSB, on cinder-blocks.

      If anything, our quotes might be on the low side of things.

  1. Soppheap Thong

    plan to add a story with 4 bedrooms, 2 baths and family room on the top of 1471 sq.ft house. how much is total cost?

    In Garden Grove, California, does it required 3 cars garage for more than 5 bedrooms house ?

  2. Garry

    Thanks for a realistic price reality. Been doing this for years and still scratch my head pricing additions. Cost of living is like a mirage .