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Addition Cost per Square Foot: Case Studies

Square footage is in high demand. Many homeowners are seeking to upsize their living space, whether it’s because their family is growing, they’re spending more time at home, or they simply want more space. With the current housing market making it difficult to buy a home at a reasonable price, some choose to simply add on to their current home rather than buying a new home. So how much does an addition cost per square foot?

Because additions come in many different shapes and sizes, this is a difficult question to answer. The best way to estimate the cost per square foot of a home addition is to examine a few real-world examples. As a remodeling firm that specializes in custom-designed home renovations, Lamont Bros. has performed dozens of home additions in the Portland area. 

In this article, we’ll take a look at five different types of home additions using previous Lamont Bros. projects as case studies. We’ll discuss the cost per square foot of each addition, adjusted for inflation to 2022 dollars. This article will also provide a description of each project to give you a better understanding of how design can affect the cost.

The three standard types of additions you’ll read about are:

Single-story addition

The simplest and most common type of addition is a single-story addition. Usually, these are attached to the side of the house at ground level. Most homeowners use single-story additions to build a master suite, additional bedrooms, or more shared living space. Single-story additions tend to have the lowest base price due to their simplicity.

One of our most recent single-story additions was for a home in West Linn, OR. The homeowner, an avid pinball machine collector, wanted a game room for their collection. In terms of design, the addition was relatively simple; a rectangular 655 sq. ft. space with enough power outlets to run 30+ pinball machines at once. 

The total cost of this addition was $243,000, bringing the total cost per square foot to $371.

West Linn Single Story Addition

  • Level: Ground
  • Number of stories: 1
  • Foundation type: Crawl space
  • Shape: Rectangle
  • Room use: Game room
  • Added space: 655 sq. ft.
  • Cost: $243,000
  • Cost per sq. ft.: $371

Second-story addition

Built over top of an existing level, a second-story addition tends to be towards the top in terms of cost. This is because second-story additions often require structural reinforcement on the lower levels, adding to both the design and building costs. They also tend to be less accessible than ground-level additions, and thus create more work for the construction team. 

Second-story additions typically make excellent space for additional bedrooms and/or bathrooms. Home offices, theaters, or multipurpose rooms are also common. They are a great solution in homes with limited options for outward expansion due to property boundaries. 

In 2021, we built a second-story addition for a family in the Cedar Mill neighborhood. The homeowners wanted to add a master suite above their existing living room/kitchen. Our final design included a 717 square foot addition with a master bedroom, master bathroom, walk-in closet, and private office space. 

Like most second-story additions, the challenges with this project were primarily structural – the first story on which the addition was built needed to be structurally reinforced before the addition went on. We also had to extend the chimney higher to compensate for the higher roof. In the end, the total cost for the master suite addition ended up being $365,000, for a cost per sq. ft. rate of $509.

Cedar Mill Second Story Addition

  • Level: Second
  • Number of Stories: 1 (Existing Lower)
  • Foundation type: Floor below
  • Shape: Rectangle
  • Room use: Master suite/office
  • Added space: 717 sq. ft.
  • Cost: $365,000
  • Cost per sq. ft.: $509

Two-story addition

Believe it or not, there’s a difference between a second-story addition and a two-story addition. With a two-story addition, the addition consists of two stories built at ground level. A second story addition involves building a second level on top of a pre-existing story. 

The primary advantage of a two-story addition is that it is an incredibly efficient use of space. You get twice as much square footage as you would with a single-story in the same footprint. For this reason, the cost per square foot of a two-story addition can sometimes be lower than that of a single-level addition. 

Two-story additions are incredibly versatile and can add virtually any kind of living space to a home. Homeowners often use them to add extra living space downstairs and more bedrooms upstairs. It’s also not uncommon to design a two-story addition to function as its own separate living space, like a mother-in-law suite. 

Recently, Lamont Bros. built a two-story addition in Beaverton. The homeowners wanted to add a bedroom, bathroom, and den to the downstairs and a multi-use bonus room with a balcony to the upstairs. We built a 998 square foot addition for a total project price of $347,000. At a cost per square foot of $348, this two-story addition was less expensive per square foot than the single-level addition even though the total job cost was more.

Beaverton Two-Story Addition

  • Level: Ground
  • Number of Stories: 2
  • Foundation type: Crawl space
  • Shape: Rectangle
  • Room use: Bedroom, bathroom, den, multi-purpose
  • Added space: 998 sq. ft.
  • Cost: $347,000
  • Cost per sq. ft.: $348

Basement & Kitchen Additions

In addition to these three main types of additions, we also see a fair amount of additions involving basement and kitchen space. These types of additions tend to be much more expensive and less predictable than those mentioned above.

Basement Additions

A typical basement addition involves adding a basement to a house. This means digging out the foundation and building downward rather than up. Due to the cost of excavation and concrete, basement additions are extremely expensive. They often involve specialized digging equipment and difficult permitting procedures. Because building underneath a home can present many different challenges, it is nearly impossible to estimate the general cost of basement additions.

Kitchen Additions

It’s also common for homeowners to add space to their home while also remodeling their kitchen. These kitchen additions often have a very high price per square foot simply because of the cost of the kitchen itself. 

For example, in 2020, Lamont Bros. did a $228,000 kitchen remodel that added 109 square feet to the client’s house. Due to the cost of the kitchen remodel, the cost per added square foot was $2,089. However, most of the project budget didn’t actually come from adding space. Rather, it was in the cabinets, countertops, and appliances that are standard features in any kitchen remodel.

Like basement remodels, it is difficult to accurately calculate the cost per square foot of a kitchen addition because the cost of the actual kitchen remodel varies so greatly from project to project. 

Overall Average

The term “home addition” covers a wide range of projects with different sizes, needs, and ultimately, costs.  As a result, generalizing the cost of additions per square foot is a difficult and often unhelpful calculation. That said, if you still want to know the average cost of an addition per square foot, you can have it.

Over the past 3 years, Lamont Bros. has performed 12 substantive additions in the Portland area. Of those, three were major outliers in terms of cost per square foot. Those were not factored into this average.  

Among the other 9, the average cost per square foot was $469.

Keep in mind that several factors will affect the cost per square foot of your own addition. It could be less than this average, or it could be more. Chances are, a single-story addition or a two-story addition will be around or below this average. Second-story additions, basement additions, and kitchen additions will likely be higher.

To learn more about what cost factors might affect your home addition, read our article, “What Factors Affect the Cost of a Home Addition?

Thinking about an addition for your own home?

Now that you have a strong understanding of the different types of home additions and what they might cost per square foot, take the next step. Head over to our additions portfolio to look at examples of other home additions Lamont Bros. has built in the Portland area. You can start gathering inspiration for your own home addition, too.

If you’re ready to start making big decisions for your home, we’d like to meet you. Lamont Bros. has guided dozens of Portland homeowners through the process of designing and building their dream addition. Click the button below to schedule a free video call with one of our professional design consultants.