home addition framing

What is the best size for a home addition?

If you’re considering a home addition to increase your living space, it’s important to get it right. You don’t want to overspend on space you don’t need, but you also want to make sure the addition is worth your time and money. Determining the best size for your home addition can be a challenge, but it’s an important step in the process of building an addition that meets your needs.

At Lamont Bros., we have extensive experience working with homeowners in the Portland area to enhance their homes. When designing an addition, one of our goals is to provide clients with the optimal amount of space for comfortable living.

In this article, we’ll share some remodeling best practices to help you determine the best size for your home addition. By understanding how your lifestyle impacts your home’s need for additional space, you’ll be able to plan an addition that meets your requirements. Topics we’ll cover include:

Why the size of your addition is important

When you build an addition to your home, it’s usually because you need space. But how much space do you need? Better yet, how much is too much, and how little is too little? Before you decide how big your addition should be, it’s important to understand why the size of your addition matters. Here are two big things that your addition’s size may affect.

Project Cost

Whether too big or too small, a poorly sized addition can result in inefficient project costs.

Larger additions cost more money to build — they require more space, material, and labor. These costs can quickly add up, so keeping your addition to a reasonable size can save your budget.  If you build an addition that is larger than you need, you’ll end up wasting money on the unnecessary square footage.

On the other hand, small additions can be inefficient in that they tend to cost much more per square foot. An addition’s cost per square foot isn’t linear — it decreases as the addition grows in size. This is because additions have what is called static costs. These are costs that remain the same regardless of the size of the addition, such as permitting, demolition, and tie-in. With a small addition, those static costs make up a larger percentage of the total bill.

An addition should increase your home’s square footage enough to justify the cost fo the project.

Design Functionality

The size of your addition will also influence how you use the space. Too much, and you won’t know what to do with it. Too little, and you won’t have enough to do what you want.

An addition that is too large may end up with a lot of unused space that you still spend money to heat and cool throughout the year. Or, if the addition takes up too much of the land lot, it may limit usable outdoor space. It’s also possible for an addition to be so large that it interferes with the visual design proportions of the home.

However, an addition that’s too small can present different challenges. Namely, it fails to solve the issue it was designed to solve: provide the homeowner with an adequate amount of space. Even if the addition manages to free up space elsewhere in the home, the space within the addition itself can still become cramped and cluttered. For example, a kitchen addition can open up the space where your old kitchen was. However, if the space for the new kitchen is too small, it can make for a very uncomfortable cooking experience.

What May Affect the Size of Your Addition

When designing your home addition, there are a handful of factors that will influence how large your addition should be. Here are the most common.

Type of Space

The factor that has the greatest impact on your addition’s size is its intended use. Different types of room uses will require a differently sized structure. For example, a bathroom addition will require a lot less space than a mother-in-law suite.

When planning an addition, it’s important to first establish how you want to use the space. This will inform many of the decisions regarding size and square footage.

Location on the Home

Do you plan to build your addition up or out? Where you install your new space may be limited by where you plan to build. If you’re doing a second-story addition, it’s the most cost-effective to duplicate the footprint of the home on the second floor.

On the other hand, building outward on the ground level may not be practical if you live on a small lot. Most people like to maintain at least some yard space for outdoor activities. Not to mention, setback and zoning laws can make it difficult to add to your home’s footprint.

A second-story addition is typically limited to the size of the home’s footprint.

Floor Area Ratio

In many regions, the maximum square footage of a home is limited by Floor Area Ratio. This is a measurement of the home’s floor area to the land lot’s size. In Portland, most single-family homes can be between 40-70% of the lot’s total square footage.

Lifestyle Changes

The size of a home addition depends primarily on the homeowner’s needs, which can change over time. As families grow older, they often require more bedrooms and bathrooms. At the same time, the increasing prevalence of working from home has led to a need for separate office spaces. Some homeowners also plan for the future by making their homes more accessible in anticipation of aging.

So, how big should my addition be?

The intended space use of the addition has the most direct impact on its size. Below is a list of common space uses for home additions and their correlating square footage.

Bathroom Addition — 18 – 120 sq. ft.

Standard full bathroom designs with a sink, toilet, shower, and tub are usually 5’x8’, or 40 square feet. A half-bathroom with only a toilet and sink can squeeze down to 18 square feet. On the other hand, a master bathroom can easily be over 100 square feet.

Kitchen Addition — 100 – 250 sq. ft.

A kitchen addition is often loosely defined. In some cases, it means building an entirely new area for a kitchen. Other times, it means building extra space to extend the current kitchen. A full kitchen addition requires room for a minimum of 30 linear feet of cabinetry plus appliances.

Bedroom Addition — 70 – 200 sq. ft.

Legally, a bedroom in Portland must be at least 70 square feet. However, for the sake of comfort, most experts agree that 120 square feet is the minimal bedroom size. You may be tempted to build smaller bedrooms for your kids while they’re young. Before you do this, consider that your kids will grow up and will likely need more space as they do.

Primary Suite Addition — 300 – 500 sq. ft.

A primary suite includes a bedroom, an attached bathroom, and 1 or 2 closets. The bedroom should be able to comfortably accommodate a king-sized bed and several dressers. At the same time, the bathroom should be large enough to fit a toilet, side-by-side sink, freestanding bathtub, and walk-in shower.

Mother-In-Law Suite Addition — 600 – 1,200 sq. ft.

As a separate living space, a mother-in-law suite should have all the basic necessities. A well-designed suite will have a bedroom, full bathroom, kitchen, and living area. Some homeowners build a mother-in-law suite attached to their home, while others build them as separate structures called accessory dwelling units.

Want a designer to help you plan your addition?

By now, you should have a firm understanding of what may affect the size of an addition. You should also have a better idea of how large your addition project must be in order to adequately serve your needs. Now, take the next step. Check our Additions Portfolio, where you can gather inspiration on previous addition projects by our team at Lamont Bros.

Don’t want to face the process of building your addition alone? Let us help you. Our team of seasoned design and construction experts will guide you through the process of creating an addition that perfectly fits your needs. Click the button below to schedule a free design consultation.