If you want more space in your house, don't call a contractor. Instead, train your rooms to multitask.

"When you convert a minimally used room into a frequently used room, you essentially have built an addition onto your home for zero cost," explains Jeff Bredenberg, author of "How to Cheat at Organizing" (Taunton, $15).

Modern homes contain a lot of dead spaces. The most obvious are the no-kids-or-pets living room and the just-for-dining room. If you've done away with these — as experts have been advising for years — you understand that living well is about defining space according to what works for you.

It's an equation that needs constant refinement and a cold, impartial eye. Stroll through your house and really look at how space is used. Then make a list of the things you want to do in your home, regardless of whether you think you have the space to do them.

Maybe you long for a quiet place to do e-mail correspondence. A desk on the second-floor landing might be just the ticket.

Or perhaps you dream of a library. A bookshelf-lined hallway would house a large quantity of words of wisdom.

As for that private retreat for reading, painting or simply dreaming, a corner of a bedroom, sectioned off with a folding screen, might be all the space you need.

This sort of flexibility "is not simply a good idea; it is the only idea," declares Caroline Clifton-Mogg, author of "Apartment Living" (Ryland, Peters and Small, $30).

Her small-space primer showcases rule-breaking ingenuity. There's a fashionista with a "major shoe collection" who displays her prizes in glass-fronted hutches in the dining room.

And a homeowner who's built a kitchen banquette with pull-out file drawers in the base and sides.

And there's the Parisian who added a whirlpool bath to the bedroom, encased it in oak and topped it with a lid. Off-duty, it looks and functions as a piece of furniture.

Le Corbusier, the great Bauhaus architect, thought built-in fittings should "take the place of much of the furniture, which is expensive to buy, takes up too much room and needs looking after." His precepts are essential to Clifton-Mogg's book and a stylish companion, "Small Spaces" (Ryland, Peters and Small, $20) by Rebecca Tanqueray.

Built-in storage, in the form of bookcases or clean-lined walls of cupboards, covers entire living room walls and poses as three-quarter-high room dividers. It wraps around doorways, shelters sofas, lines window niches and serves as bed headboards, providing a welcome space to hold alarm clocks and nighttime reading.

As for desk space, both authors are keen on what Tanqueray calls "a working wall" — a long, sleek work surface that runs across one wall. It's a non-desky desk that invites you to pull up a non-desky chair and add cabinets or drawers for under-the-counter storage. Clear the papers away and you can set out trays of hors d'oeuvres.

Like rooms, furniture needs to multitask. That means there's no need for a matched set of dining chairs to stand at attention. When it's time for a dinner party, chairs can be gathered from other rooms to create an eclectic mix rather like your guests — unique and full of character.

For a coffee table that multitasks, you can stack books, set out a trunk or opt for a higher tea table so that it's easier to position a laptop by the sofa.

Used as a coffee table replacement, the ottoman not only holds your feet and your newspaper but provides an extra perching spot for party guests.

In a small space, two petite ottomans work better than one large one. They can travel around the room or be tucked under a table when more floor space is needed.

Better still are upholstered cubes that can be clustered together, positioned next to armchairs or pulled up as seating.

Small spaces, says Tanqueray, are "the next big thing." The reason certainly has to do with the size of their financial and environmental footprints. But people are drawn to small spaces for their comfort and coziness.

When you live in them well, you choose only the possessions you really love and make space for only the things you really want to do. Like a rigorous personal trainer, they transform you into a clean, lean living machine.