Design Vogue

Few homeowners will ever say that they want less space. Once you live in a house for a while, the house always seems to get smaller with the constant accrual of furniture, pets, people, and belongings over the years. One solution is to build an addition. But full-size additions can drain your bank account. A house bump-out addition could be the answer.

House bump-outs offer a tantalizing solution to the space and money problem. If you need less space (or cannot afford a full addition), try a room addition—one room tacked onto the side of the house, typically a bedroom, bathroom, or some additional area in the kitchen. Keep reading to learn more about bump-out additions and how they can offer a bit more square footage in your home.

House bump out space with large windows, couch and dining table — Credit:
The Spruce / Christopher Lee Foto

What Is a Bump-Out Addition?

A bump-out is an extra space that is far smaller than a full addition. It may be the same size as a single room, but sometimes it does not match the size of a room addition. In other words, the bump-out is seen more as an expansion of a room, not of the house itself.

So, there are no standard rules about what makes a bump-out, in terms of size or project scope. Bump-outs also can employ a variety of designs and construction methods, but there are some common features and advantages that apply to most bump-outs:

As small as 2 feet: Bump-outs may extend as far as 10 to 15 feet from the house, but they can also be tiny pop-outs that are no deeper than 2 feet.
Cantilevers: Small bump-outs often are cantilevered (unsupported by posts) from the house. This is typically limited to about 2 feet in depth. One advantage of cantilevering is that it requires no footings or foundation walls, saving on expenses. Also, cantilevered bump-outs preserve yard space.
No extra HVAC: One benefit of bump-outs is that they often do not require additional heating or cooling services, as they can share it with the rest of the room.
Lean-to roof: Bump-outs often have shed-style (lean-to) or flat roofs, rather than extending the existing roof.
Minimal exterior changes: Bump-outs, due to their small size, do not substantially change the exterior of the house. They often blend in seamlessly with the main house.

Bump-Out Addition Pros and Cons

Pros

Less expensive than full-size addition
Minimal visual impact
Blends well with interior space
Extra HVAC often not needed

Cons

Higher per-square-foot cost than full-size addition
Requires full set of permits
Extra space may fall short of expectations
Foundation must be built

Bump-Out Addition Costs

On average, expect to pay anywhere from $10,000 to $43,000, with an average of $27,000 for a bump-out addition.The type of house, location, and lot size and shape may increase or decrease the price of the addition. The bump-out will also require wiring, plumbing (for bathrooms or kitchens), HVAC (for larger bump-outs), foundation, roofing, and windows as additional costs to factor in.

While the total cost of a bump-out is less than that of a full-size addition, a bump-out will cost more on a square-foot basis. This is because a large part of the cost is in initiating the project, making drawings, pulling permits, opening up the side of the house, pouring a foundation footer (as applicable), calling in an electrician to move wires, and so on. You may need to do the same things with a bump-out as you would do with an addition, just on a smaller scale. Costs vary wildly because they change according to homeowners' desires, locality, and a host of other factors.

How Can a Bump-Out Add Significant Space?

A bump-out that extends 3 feet from the house and is 15 feet wide adds 45 square feet to the home. This would not be considered a major space-maker relative to the entire house. These 45 extra square feet would only add 3% to a 1,500-square-foot home.

Bump-outs are often installed in rooms that are already very small—often so tiny that they are barely functional. A 150-square-foot kitchen, when bumped out another 45 square feet, receives a 30% boost in space. Increasing the kitchen by one-third can be enough space to make the kitchen easier to work in.

Suggested Uses for Bump-Outs

Because most bump-outs are not full rooms, they tend to enhance an existing room. Homeowners commonly use them to provide just enough extra floor space for specific goals, such as:

Adding a window seat with bookshelves
Installing a bathtub in a bathroom that currently only has a shower
Extending the length of the counter, adding space for an appliance, or installing a kitchen island
Providing a kitchen with enough extra space for a dining area or breakfast nook
Enlarging a bedroom to accommodate a second person
Enlarging a bedroom to accommodate more closet space
Converting a bedroom into a suite, complete with a bathroom and walk-in closet

How Far Can You Cantilever a Bump-Out?

Grade-level (first-floor) bump-out additions can be cantilevered or have simple foundations. They can rest on a concrete slab or foundation walls, which can create a crawl space. Upper-level bump-outs, when short, are small enough that they can be cantilevered from the second-floor framing. Cantilevering may not take a bump-out addition very far out, but the advantage is that you avoid having to build a ground-level foundation.

When you choose to cantilever a bump-out, the dimensions of your house's joists dictate the depth of the bump-out. Generally, bump-out additions can be cantilevered at a distance equal to four times the size (depth) of the floor joists. For example, a 2x8 joist has a depth of 7 1/4 inches; you can cantilever from 2x8 joists a maximum distance of 29 inches.

Nominal Joist Size	Actual Joist Depth	Distance of Bump-Out Cantilever
2x6	5.5"	22"
2x8	7.25"	29"
2x10	9.25"	37"
2x12	11.25"	45"

In addition, for every foot that you cantilever outward, the cantilevered joists must extend twice that length along an existing joist. For example, if your bump-out cantilevers 2 feet, you have a minimum of 4 feet running alongside an existing joist inside the house.

FAQ

How far out can you add a bump-out?

A bump-out addition can be as shallow as 2 feet and as deep as 15 feet.
Can you DIY a bump-out?

Even the most experienced DIYers should leave a bump-out project to the professionals. The overall construction, installations such as plumbing, electrical, and HVAC are always best left to the experts. If your bump-out does not require any mechanical installations and is just framing, drywall, and flooring, you should still hire a professional, as they can ensure that your addition is safe and built correctly.
Is a bump-out worth it?

If the bump-out is added to increase the functionality of a room, such as a small kitchen or bathroom, it will be worth it and will likely increase the value of the home. If the addition was for aesthetic purposes such as a window seat, the disruption may not be worth it for some homeowners.