Dollar for dollar and bang for buck, basements and attics are among the more cost-effective ways to increase a home's value. These projects don't pay off as handsomely as some others; on a national basis, a midrange basement remodel recovers 78.8% of its costs, and a midrange attic remodel 79.9%.

But often, basements and attics more than pay for themselves. And both can be affordable ways to "add on" without pouring concrete, framing exterior walls, or otherwise, well, adding on.

"Attics are awesome," says Minneapolis remodeler Michael Anschel. His attics typically become master suites for parents seeking their own living and relaxing space, and cost from $60,000 to $150,000. In Seattle, Jackson Remodeling often undertakes "major structural work" to expand attics into larger master suites costing from $150,000 to $200,000, Leif Jackson says. Other common attic conversions include guest bedrooms, as well as home offices. Basement remodels vary widely depending on region, age of house, and homeowner's lifestyle. Gary Potter of Potter Construction, Seattle, agrees with our cost averages, but notes that a multitude of factors can push costs higher, such as low ceilings that require the house to be raised or the floor lowered.

Fellow Seattle remodeler Denny Conner says that his basement remodels usually start at $100,000. "But if it's done well so it doesn't feel like a basement, I'd say our clients could get 100% of their money back," he says.

Legal considerations can also have an impact on basement values. Jackson Remodeling often upgrades windows and builds closets to meet egress requirements, enabling clients to legally claim basement rooms as bedrooms. In Boise, Idaho, basement remodels recoup 123.9% of cost, but that may be because unfinished basements can't be considered in the appraised value of living space, explains Bill Keilty of Keilty Construction.

For the new suburbanites of Provo, Utah, "it's not if but when they're going to remodel" their huge, unfinished basements, says Cory Hogan of Upscale Downstairs. His costs average $20 to $25 a square foot for basements that are 1,500 to 2,000 square feet. Basement remodels in nearby Salt Lake City recoup 85.4% of their cost at sale.

"The biggest thing is home theaters," he says. "I think more people just want to get the big ugly TV out of their formal spaces upstairs and into the recreation space downstairs."

Also popular in new homes -- particularly in humid regions -- is the Owens Corning Basement Finishing System, made of moisture-resistant fiberglass panels that can be installed in a week. Jim Quigley, whose Midwestern franchises expect to install $25 million worth of systems this year, says his basement remodels typically cost $20 to $40 a square foot, excluding plumbing. Customers "are getting back their money, especially if the house next door is just like theirs and the only difference is the basement," he adds.

Attic Bedroom Remodel

Convert unfinished attic space to a 15-by-15-foot bedroom and a 5-by-7-foot bath with shower. Include a 15-foot shed dormer, four new windows, and closet space under the eaves. Insulate and finish ceiling and walls. Carpet floor. Extend existing HVAC to new space; provide electrical wiring and lighting to code. Retain existing stairs, but add rail and baluster around stairwell.

Basement Remodel

Finish the lower level of a house to create a 20-by-30-foot entertaining area with wet bar and a 5-by-8-foot full bath; construct 24 LF of finished partition to enclose mechanical area. Walls and ceilings are painted drywall throughout; exterior walls are insulated; painted trim throughout. Include five six-panel factory-painted hardboard doors with passage locksets. Electrical wiring to code.

Main room: Include 15 recessed ceiling light fixtures and 3 surface-mounted light fixtures, and a snap-together laminate flooring system.

Bathroom: Include standard white toilet, vanity with cultured marble top, resilient vinyl flooring, two-piece fiberglass shower unit, a light/fan combination, vanity light fixture, recessed medicine cabinet, towel and paper-holder hardware.

Bar area: Include 10 LF of raised-panel oak cabinets with laminate countertops, stainless steel bar sink, single-lever bar faucet, under-counter refrigerator, and vinyl floor tile.