Bump-out additions: How to get more room without the expense of a full addition

If you're thinking about a small home addition or extending a room by just a few feet, a bump out addition can be a great alternative to a full add on, and save you thousands in the process.

Glass box extension
(Image credit: IQ Glass)

Wish your kitchen was a tad bigger so you could fit a breakfast table? Maybe you’d like a soaking tub in your master bath but none of the models you’ve found will fit. You can add just a few feet to your home without the headaches and expense of a full-blown room addition with a bump-out addition. Also called a micro-addition, if you think a bump-out would solve your design needs, this post will answer all your questions.

What is a bump-out addition?

Typically, a bump-out addition is cantilevered off the existing foundation, similar to a balcony, making foundation work unnecessary. And, a micro-addition doesn’t need to be tied into the existing roofline. Both of these qualities save both time and money, while still adding extra space.

The most notable difference between a bump-out and a room addition is size. Bump-outs are small. Like just a few feet small, which obviously saves on the materials cost. Bump-out additions are limited in size due to the fact that they do not have a separate foundation.

Also, micro-additions rarely require additional heating or cooling. The vents from the room to which the bump-out attaches will adequately provide service to the additional square footage. Just don’t install plumbing lines in the unheated area.

  • Keep reading: Home addition costs - price per square foot, where to save, and financing options

How big can you make a bump-out addition?

The weight of a cantilevered bump-out is held by the home’s existing floor joists. The larger the joists, the larger your bump-out can be. According to Manny Angelo Varas, president and CEO of the MV Group, luxury home builders in South Florida, a floor joist can extend four times the depth of the joist. For instance, if your joists are 2x10s, they are 9 ¼ inches deep. Multiply that measurement by 4 and your micro-addition can extend 37 inches.

Homeowners typically add bump-out additions to the first floor of the home. But you can also add one to the second floor. And, if your home is built on a concrete slab, you can still add a bump-out. According to Varas, a slab can support a 3-5 foot cantilever.

Reasons to add a bump-out addition on your home

Other than cost savings, there are several reasons homeowners choose a bump-out over a full-blown room addition. The most obvious reason is they only need a few more feet inside the home. But there are other reasons outside the home as well.

According to Varas, you will need a building permit for a micro-addition. So, before considering any home remodeling, check with your building officials for permitting requirements and zoning setbacks. If your home already sits close to your property line, your setbacks could be too tight for a full home addition. That’s a great opportunity for a bump-out.

You might also consider a bump-out to protect mature trees and their roots. By cantilevering the addition off the existing foundation, you can add space to your home without disrupting the soil. And, tree roots aren’t the only thing underground. The foundation work that a full-size home addition requires could necessitate moving below-grade plumbing or utility lines. The labor of moving those lines adds to the overall cost of the remodel.

Finally, if your yard is too small to accommodate the access and maneuvering of the heavy equipment needed for foundation work, adding a bump-out still provides more square footage.

How much does a bump-out addition typically cost?

According to the online home services marketplace, Homeguide, the average room or home addition costs between $86 and $208 per square foot. At this rate, a typical home addition could cost $20,000 or more. But, because a bump-out lacks some of the factors that drive up the cost, a 2-foot kitchen micro-addition could cost as little as $5000.

Two feet may not sound like a lot. But if you consider running it the length of a 15-foot room, that gives you an additional 30 square feet. That’s plenty of room to add a breakfast table, pantry, or center island.

Why are bump out additions cheaper than a full addition?

Since construction costs are often calculated by the square footage, just the smaller size of a bump-out makes them cheaper than a room addition. However, there are other factors that come into play. Lack of foundation is the primary one. Other factors depend on the size and function of the addition, which could mean you won’t need the following:

  • Wiring
  • Plumbing
  • HVAC ductwork
  • Extending the existing roof
  • As many windows as a full room addition

Bump-out addition pros and cons

Before getting into the pros and cons of a bump-out addition, Varas advises homeowners to ask themselves, “Do you want to live in the home and just enjoy it or do you want to create future value?”

Enjoying your home remodel every day takes the sting out of the high cost of a full-sized addition. But, if you only feel the pinch of a small dining room when everyone is home for Thanksgiving, a bump-out, and its smaller price tag may be your best option. Especially if you know you’re in your forever home.

But, if you see yourself selling in the future, Varas says that bump-outs don’t add much value to the home or bring a considerable return on investment. “A full-sized addition creates future value for resale that a bump-out doesn’t,” he says.

Otherwise, the pros and cons of a bump-out addition are:


  • Lower cost
  • Just enough space for what you need
  • Lose less yard space
  • Protect mature trees
  • Blends seamlessly with the existing structure


  • Adds space to only one room
  • You may have trouble matching your siding
  • Kitchen and bath bump-outs may require plumbing lines, depending on your layout
  • Not for the average DIY-er

Ideas for bump-out additions

Varas says that the most popular use for a micro-addition is to expand the same space. Here are a few ways homeowners use their bump-out additions to bring functionality and joy to the home.

  • As a bay window with a window seat in the living room or den.
  • To expand the master bath, making room for both a soaking tub and a shower.
  • In the kitchen, to add dining space, room for an island or pantry, or larger appliances.
  • To add a walk-in closet to a bedroom.
  • To add a laundry room or mudroom.
  • As a home office nook off the family room.

Finally, always consult with a qualified professional before embarking on any home addition, especially a bump-out. If not properly supported, a cantilevered micro-addition can sag, leading to structural damage to the home. It can also leak causing mold and water damage. And to avoid further complications, always follow the local zoning ordinances, building codes, and HOA regulations.

Carol J. Alexander

Carol J. Alexander writes website copy, blog posts, and feature articles on home remodeling and construction topics from her home in the Shenandoah Valley of Virginia. In addition to Real Homes, notable clients include, This Old House, Family Handyman, and Florida Roofing magazine.