A bump-out addition hangs the new living space off the side of the house, with no need for a new foundation—and sometimes little or no roofing work necessary either. That can save you 15 to 30 percent compared to a full-scale addition, but you're limited in how big the expansion can be. In general, a bump out can project a maximum of 3 feet from the house and stretch 10 to 12 feet long, says Curt Schultz, a Realtor-architect-builder in Pasadena, Calif. What can you do with a long skinny addition like that? Here are five possibilities:

Turn an L-shaped kitchen into a full U. If your kitchen is wide enough for cabinets on only two adjoining walls, a bump-out addition can yield enough extra space to add a third wall of cabinets and countertops, turning an L-shaped kitchen that's short on storage and work surface into a generous U-shaped kitchen—perhaps even with an island in the middle.

Separate the master bathroom shower and tub. Most older master bathrooms have a combined tub and shower, which is space-efficient—but less than ideal for either showering or bathing. A separate shower means no stepping over the tub wall to get in, plus you can have body sprays all around you. A separate tub needs no walls, curtains or glass doors around it—and it can be deeper than one with a shower attached. A bump-out addition can yield the added square footage needed to separate your tub and shower.

Create a walk-in wardrobe closet. A few extra feet tacked onto the master bedroom might not seem like a lot, but it can be just what you need to expand your wardrobe closet from a cramped pole-and-shelf setup to a full walk-in with adjustable shelving, cubbies and other functional storage options.

Put an eating area in the kitchen. Many pre-war houses' kitchens are too cramped to fit an eating area. You could build a large conventional addition to accommodate a table and chairs. Or use a kitchen island, peninsula or diner-style booth, which require less space than a table and chairs—and can often be accommodated by a bump out, at a fraction of the cost of a full-fledged addition.

Turn an extra bedroom into a family room. Got a spare bedroom that's underutilized? A bump out addition can turn a modest room into one with plenty of space to serve as a TV room, home office, family room or playroom—or a multipurpose space that serves as all of the above. The money you'll save by bumping out (especially if the room is on the second floor) might just finance the flat-screen TV, computer or built-in bookshelves you'll put in the space.