What To Know About Building a Bump Out Addition

If your home could use a little extra room but you lack the space or budget for a full addition, a “bump out” may be the perfect solution. These home additions, though modest in scale, can have an outsized impact on look and feel of your living space.

What Is a Bump Out?

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It’s an expansion of a home’s square footage gained from pushing a wall outward — the “bump” — rather than building up. While some people might refer to a full room added this way as a bump out, the phase more commonly describes areas in the 10- to 30-sq.-ft. range.

A bump out can be added to a finished home or be part of the original floor plan. When added as a remodel, they can be cantilevered or built on footers.

What’s the Difference Between a Bump Out and an Addition?

A bump out is a subset of home additions. Specifically, it expands a single wall or section of that wall outward to create additional space in a single room.

There’s no hard-and-fast dividing line between a bump out and a full addition. In common usage, an addition that involves expanding more than one wall or adding more than 30- or 40-sq.-ft. typically isn’t called a bump out.

Pros and Cons of a Bump Out

Pros

• Adds variety to exterior profile: A bump out changes the profile, sometimes resulting in a more interesting appearance. It’s a bit like adding dimensional roof shingles, which are typically regarded as more attractive than flat three-tab shingles.
• Provides extra space: Bump outs provide a little more room in tight spaces — say, for adding a reading window bench or breakfast nook.

Cons

• Can create a “constrained” feel: Poorly designed bump outs can create pinch points that constrict access. Doing it right means putting thought into the process and double-checking all your work.
• Can be expensive: Bump outs require more of a cash outlay than most DIY improvements.

Best Rooms for Bump Outs

Anywhere a relatively small amount of additional space will make a big difference, in mobility or visually, is a good place for a bump out. Closet bump outs allow a walk-in closet without the cost of a full remodel, while bathroom bump outs can convert a half bath into a full bathroom. All give a corresponding boost to home value.

Ladina Schöpf — an architect, building site manager and the founder of LS-Projects — has seen the dramatic impact a bump out can have.

“In one project, I worked with a homeowner who wanted to add a small bump out to their kitchen to create a cozy breakfast nook,” she says. “This not only increased the functionality of the space, but also added aesthetic value to the room and brought a lot of light in thanks to the big windows.”

Sometimes the choice of location addresses the homeowner’s specific needs. One of the best use of bump outs I’ve seen allowed a homeowner’s daughter greater mobility in her wheelchair. A few well-placed bump outs in the kitchen, bedroom, bathroom and one hallway made it significantly easier for her to navigate without assistance.

Building Permits and Codes for a Bump Out

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Permits vary by municipality, but in general, all work that expands the footprint of your home will require some permitting. This is especially true if the bump out relocates any plumbing, electric or HVAC.

Julee Ireland, an interior design architect and founder of Home Renovation School, urges homeowners to invest time during project preparation.

“It’s important to have a set of plans drawn up, or to draw a set yourself if you have the skills, so you can clearly communicate the addition to your contractor and to the city for approval,” Ireland says. “You or your contractor will need the design and measurements to accurately build your scope of work and budget.”

Average Bump Out Cost

The price per square foot is high compared to a larger addition, since many of the costs are duplicated on the smaller project. Think of it like buying a snack-size bag of chips vs. a family-size bag. The total cost of the snack-size is lower, but the cost per ounce is higher.

In general, a bump out will cost $300 to $600 per square foot. This price will go up if you need electrical, plumbing or HVAC work.

Is a Bump Out a DIY Project?

Doubtful. A bump out is a complex project, best left for experienced DIYers.

It takes a fair amount of skill, planning and preparation. You’ll almost certainly need to modify a load bearing wall, as well as cantilevering or placing a foundation, and potentially changing the electric, plumbing and HVAC systems. That’s in addition to the siding, roofing and drywall work that’s guaranteed to be part of the project.

This complexity means most homeowners opt to bring in a pro. But if you’re looking for more details on DIY bump outs, start with this overview of a successful bathroom bump out.