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Bump Out

This Lower Cost "Micro-Addition" Can Add Significant Space to a Small Room

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house bump out

Classic House "Bump Out"

Copyright Shutterstock via Black & Decker The Complete Guide to Room Additions
We're all in need of more space in our houses. When you want an entirely new room--another bedroom, bathroom, or an office or sewing room--you put in an addition. If you still want an entire room but are content if it is not fully functional*, you can add a sunroom.

Need even less space than that? That's called a bump out.

Bump Out or Addition?

But you'll find little information on bump outs; they occupy a kind of hazy demi-monde in the remodeling world. Full-size additions and even sun rooms tend to get most of the attention. Builders love them because they generate the most revenue. Homeowners love them because they can add appreciable space onto their house in the form of another room, which is valuable when trying to re-sell the home. The poor little bump out can never be called a room, and as we will see, it's not even your cheapest option.

And there are differing opinions. Home renovation writer Michael Litchfield (In-Laws, Outlaws, and Granny Flats, The Taunton Press, 2011) says that bump outs, in his definition, are essentially in-law suites (full rooms) that are attached to the house.

My definition runs along the lines of Black & Decker The Complete Guide to Room Additions, which calls a bump-out an addition to an existing room, but not a room itself.

What Is a Bump Out?

While not rigid rules, the following provide a general profile for the majority of bump outs:
  • Extend from the house from 2 to 8 feet.
  • On an upper story, a bumpout can be cantilevered (unsupported by posts) as far as 2 feet.
  • Do not require additional heating or cooling.
  • Require additional horizontal bracing to compensate for lost studs.
  • Typically serve just one function (see below for suggested uses).
  • Have a shed (lean-to) or flat roof, rather than extending the existing roof.
  • Not meant to substantially change the exterior of the house; only to add inside space.

How Can a Bump Out Add "Significant Space?"

A bump out extending three feet from the house, at fifteen feet wide, would in most cases not be considered a major space-maker. After all, that's only 45 square feet.

However, bump outs are often installed in rooms that already quite small. So, a 150 square foot kitchen, when bumped out another 45 sq. ft., receives a space increase of about a third.

Suggested Uses For Bump Outs

Because bump outs are not full rooms, they tend to enhance an existing room. They can:
  • Provide space for a window seat with book shelves.
  • Allow for installation of a tub.
  • Give you enough room in your kitchen to put a length of counter, stove, and fridge. With the increased floor space in the main area, you can install a kitchen island.
  • Provides a kitchen with enough extra space to have an eating area.

Cost of a Bump Out

While the total cost of a bump out will likely be 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 footer, 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.

Costs tend to be all over the map, because costs vary according to homeowners' desires, locality, and a host of other factors. Some reports, though:

  • A 2' by 10' bump out estimated to cost $17,000. A bump out twice that size (4' by 10') priced at $30,000.
  • A 6.5' by 28' bump out for a bathroom, on ground, poured foundation: $30,000.
  • A 2' bump out in a kitchen (length not provided) on a second story, cantilevered out: $5,000
* = Sunrooms often are not as well insulated as the rest of the house, as they tend to be built largely of aluminum and glass. They may not even have electric power. It should be noted, though, that it's possible to build elaborate sunrooms or conservatories which are fully functional.

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