For the Tenazas family, it all started with the hot tub.

They had a hot tub installed on the deck of their Upper Saddle River home about three years ago. But when the weather turned cold, they found themselves dreading the thought of making the dash from the hot tub to the house.

"We were thinking that in the winter time, it's too cold to get out there," said Mary Lou Tenazas.

So they decided to turn part of the deck into more usable space by installing a three-season sunroom, at a cost of about $25,000. Now they're able to use the hot tub through more of the year, and enjoy the sunroom.

Decks are not the only place homeowners target when they want to transform little-used space into increased living areas. Basements, attics, closets, garages, even the dead space under the stairs: All can become additional living space with imagination and some remodeling.

And in the weak real estate market, remodeling underused space is a way to "trade up" without selling and moving, or even expanding beyond the footprint of the house.