Cost to Add a Room to a House

When a growing family decides their current house is too small, they really have two options: move to a new home or add a room to their current house. The cost to add a room to a house is not insignificant, but it can also come with some tremendous benefits including increased resale value and family functionality.

Here at GreatBuildz, a free service that connects homeowners in Los Angeles, Orange, and Ventura Counties with reliable addition contractors, we speak to homeowners every day about the costs of adding a room to their home.

How Much does it Cost to Add a Room to a House?

cost to add a room patio

The cost to add a room to a house can range between $300 and $500 per square foot.

Depending on what kind of room you want to add to your home, the price can vary significantly. It can range from a modest bathroom addition to a master suite addition. Let me describe the most common categories of home additions and their average costs.

Please bear in mind that construction costs vary considerably by region, so the costs listed below are specific to Los Angeles and Southern California homeowners.

How Much does it Cost to Add a Master Suite?

In Los Angeles and Southern California, the cost of adding a master suite to your house will range from $120,000 to $200,000.

Average costs and a reasonable starting budget is $150,000. A master suite floor plan can be as small as 300 square feet, but most additions are between 400 and 500 square feet or larger.  A common measurement for a master suite addition is 20×20 or 20×25 feet, but it can be any size. The price for a complete guest suite and an in-law suite are comparable. This cost is based on a one-story addition.

How Much does it Cost to Add a Bedroom to Your Home?

A bedroom addition should cost between $30,000 and $60,000 and is the simplest room to construct.

A bedroom is the least expensive because it does not require utilities or gas connections (it is a dry room). Obviously, the cost will be proportional to the size and will increase if you include additional features such as built-in cabinetry, closet cabinetry, etc. A typical bedroom is approximately a 10×10 room or a 12×12 room.

How Much does it Cost to Add a Bathroom to Your Home?

A bathroom addition to your home will cost between $50,000 and $100,000.

The cost of a new bathroom will vary according to its dimensions and amenities. Obviously, a half-bath with just a toilet and sink will cost less than a complete bathroom with a tub or shower. A luxurious primary bathroom will incur the greatest cost. The total budget will also depend on the location of your addition and its proximity to the nearest sewage & water connections, electrical lines, etc. as well as the type of foundation in your home (slab foundation vs raised foundation).

How Should You Begin Adding a Room to Your Home?

cost to add a room blueprints

Once you have a general idea of the cost and budget to add a room to your home, the next stage is to begin planning for the possibilities. After conducting research, you will need to make some broad decisions regarding the size and location of the future space you intend to build on to your home.

Consider how the space will function for you now and in the future, as well as how valuable it will be to a future buyer of your property. If the new room is functional and well-constructed, it will significantly increase the resale value of your home. However, you should not build a home that is ‘overbuilt’ for the neighborhood in terms of size or number of bedrooms. Not too many buyers want a 7-bedroom home unless they’re buying a mansion.

You will need to be aware of the zoning regulations in your area and determine whether you have sufficient space on your property to construct the desired room addition. There are two effective methods for determining your options for a room addition.

First, you can visit the city’s building department and request assistance with zoning and requirements. Alternatively, you can contact a local architect or designer and request that they visit your home to assess the viability of building a room on your home. A reputable local contractor can also guide your decisions at this early stage and provide you with budget estimates based on their recent projects.

You should also consider whether you can continue residing in the house while the room addition is being built. If the additional space is distinct from your primary residence, you may be able to live in it. However, a major room addition might make it difficult or impossible to remain in the home. Building a significant room addition to your home could be disruptive, so it makes sense to plan your living arrangements in advance.

Adding a Bedroom or Office to your Home

Numerous homeowners in Los Angeles and Southern California discover that their family has outgrown the number of bedrooms in their home. If they do not wish to relocate, they can simply add more space to their current residence, assuming there is sufficient room. Adding one or more bedrooms will increase the home’s functionality and resale value.

A bedroom can also serve as a home office, guest chamber, or for other purposes. Any such space should ideally be designed with a closet so that future purchasers will be willing to pay more for the additional bedrooms.  Unlike a restroom, this is the simplest and least expensive addition to construct because water and waste lines are not required.

Adding a Bathroom to your Home

As it is customary for older homes to have a limited number of bathrooms, adding a bathroom is a common home improvement project. In addition to resolving the practical issue of too many people sharing too few bathrooms, adding a bathroom to your property can significantly increase its resale value. Numerous homeowners and homebuyers want enough bathrooms so that adults, children, and visitors do not have to share.

Bathroom additions can be as simple as adding a powder room for visitors or as extensive as constructing a luxurious master bathroom. Due to the necessity of running water and sewage lines, the average cost of a bathroom will always exceed that of a bedroom.

Addition of a Master Bedroom Suite to a House

Numerous older residences were constructed without a proper master bedroom suite. Therefore, adults may have to share a bathroom with children (not ideal).

Despite the fact that this was the case many years ago, many homeowners today desire a master bedroom suite with its own elegant, private restroom and walk-in closet. The master suite addition is therefore a common home improvement project, despite the fact that its scale may result in a hefty price tag. People will occasionally add a second story to facilitate a private master suite.

Building a Living Room, Family Room, or Additional Room

Similar to adding a bedroom, adding a living room or family room is less expensive than adding a restroom because it does not require water or waste lines. These types of rooms consist fundamentally of four walls and a roof. In these spaces, you will still need to consider decorative elements such as lighting, built-in cabinetry, and HVAC vents.

Because these types of rooms come in a wide range of sizes, it is essential to conduct research on the ideal measurement for your intended purpose. You don’t want to have a room that is disproportionately large or small compared to the rest of the home.

Adding a Room Above the Garage

Occasionally, it is possible to add space on top of an existing residence. Depending on the location of your garage, you may be able to construct a living space above it. Creating a room addition over a detached garage is sometimes referred to as a granny flat or Accessory Dwelling Unit, which has become very popular in California following recent legislative changes.

Although the first-floor garage structure may need to be reinforced or ‘braced’ to accommodate the additional weight of the second floor, this additional living space can be added without sacrificing any of your backyard space.

Planning a Single-Story Home Addition

cost to add a room research

When planning to add a single-story addition to your home, the back or front is the most probable location (there is typically insufficient space on the side). That means you must have space in your front or rear yard to construct the addition. In addition, most municipalities require a ‘setback’ from your front or rear property line, which is the “unbuildable” area.  Therefore, the first step is to determine if you have enough space in your yard to construct the desired additional living space.

Determining how this new addition will ‘connect’ to the rest of the home is an additional crucial consideration. You want the floor plan of your enlarged home to be practical and easy to navigate. You do not want odd connections between spaces, such as adding a bedroom next to the kitchen. Early in the process, you’ll need to hire an architect to sketch your existing home’s layout on a simple plan and then determine how an addition could connect to it.

It is possible that areas of your current home will need to be reconfigured in order to accommodate your proposed addition. Keep this in mind when creating a budget…any reorganization of your existing home’s layout will incur further costs to the room addition itself.

Constructing a Room Addition to your Home

Once you’ve decided to pursue building a room addition, it’s a good idea to consult with architects and contractors to find the best fit. Occasionally, you may want to begin by interviewing contractors, and the one you choose can bring an architect with whom they have a relationship.

It is not recommended to begin by simply engaging an architect to design your home addition. When the plans are complete, it is possible that the construction estimates you receive from contractors will be higher than your budget. If this is the case, you will need to redesign your plans to fit within your budget.

Engage a minimum of one contractor throughout the entire plan design process in order to keep your home addition’s costs reasonable or affordable. I would not recommend relying on an online room addition cost calculator because each project is unique and costs vary significantly based on location.

A Few Home Addition Tips

Don’t neglect to budget for the city plan review, permit, and any other impact fees that your city will charge to allow this construction.

Always include 10-20% in your budget on top of the contractor’s estimate. You may be favorably surprised if you do not use it. In the majority of cases, however, you will encounter unanticipated expenses that will add to your budget.

Fewer alterations will be required during construction if the project’s scope and materials are outlined in greater detail beforehand. And alterations are always costly and cause delays.

When the room addition is complete, remember to add this additional space to your homeowner’s insurance policy. Also, inform your insurance agent when you begin construction to ensure that you are protected against any potential hazards.

How do I Locate a Local Home Addition Contractor?

Cost to add a room contractor

A general contractor is the only sort of contractor qualified to build a room addition at your home. No other contractor is licensed or competent to perform this complex construction work. And you should never consider employing an unlicensed or uninsured contractor to construct your home addition.

The best method to find a reliable general contractor is to ask friends and family for referrals of individuals they have worked with in the past.  If your contact had a positive experience with a general contractor, you can be reasonably confident that you will also receive quality service.

If you are unable to obtain a recommendation from friends or family, our staff at GreatBuildz can connect you with a few local general contractors who are qualified to construct a room addition in your area.

Building a room addition to your home is a substantial, expensive, and time-consuming undertaking. Therefore, you must ensure that you are working with a legitimate and trustworthy contractor. Check the CSLB website before selecting a contractor to ensure that they have an active license and no complaints.

Also, request that the contractor provide proof of insurance, including both general liability and workers’ compensation. Request that their insurance agent add you as an “additional insured.”


When it comes to planning and coordinating a kitchen remodel for your home, you shouldn’t have to go it alone – GreatBuildz can help simplify your contractor search. GreatBuildz is a free service that connects homeowners in Los Angeles, Orange, and Ventura Counties with reliable, thoroughly screened general contractors and provides project support from start to finish.


To be matched with 3 pre-vetted kitchen contractors in the Los Angeles, Orange County, or Ventura County area, call (818.317.3567) or visit our website for more information.

Hi, we're Paul and Jon - Co-Founders of GreatBuildz. We believe everyone deserves to find a great contractor, have a stress-free renovation, and enjoy their beautiful new space. There are so many contractors out there and it's often hard to tell the good from the bad... until it's too late. We started our company to help simplify your contractor search and help you have a stress-free renovation experience. We're always available to help, no matter where you are in the process. Click here to learn more about our story.

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