Craving a spacious office, yoga studio, guest suite or other new feature for your home? There’s an alternative to building an addition: You could save time and money by converting your basement, attic, garage, porch, breezeway or shed to a livable space.

These types of projects aren’t necessarily cheap. Depending on the conditions at your house, you could spend anywhere from $10,000 to $80,000 to refinish an existing space — but that’s likely half of what you’d pay for a full addition. “About 50% of the cost and effort of the typical addition is building the foundation, roof and exterior walls,” says Curt Schultz, a Pasadena, California, architect, builder and real estate agent. Here’s how to approach the job.

Select a space to convert

Staying within the existing footprint of your home makes your project simpler, less disruptive and less costly, especially if the contractor has easy access to electrical, plumbing and HVAC mains, or a simple path to run new lines. The two most popular areas to repurpose are the attic and basement, but basements may have the edge. “With attics, you often have the slope of the roof limiting the headspace and limiting your usable floorplan,” Schultz says. “In a basement, you can often get a full-height room with a bigger footprint.”

Other options that could work better than your attic: enclosing a screened porch or breezeway, or even converting your garage. Yes, you give up those spaces, but you can always rebuild them later. For a project with a small footprint like a laundry nook, powder room or office, a closet may yield the necessary square footage.

If space inside your home is tight, converting a detached garage or shed may be an option. Just remember that you’ll need a clear path for a trench to bring utilities out from the house. Whichever space you choose, make sure to check local permit requirements before making a final decision.

Figure out if it’s feasible

You may have to clear some hurdles before turning your unused space into something more functional. Building codes in the U.S. are local, says Schultz, but the International Building Code forms the basis for most of them. Most local building codes require that areas used for living purposes be accessible by a hallway or other room. Finished attics and basements must have a full stairway for access, but replacing an attic’s pull-down ladder with a stairway will mean giving up space on the floor below. Any room you’re converting to a bedroom also needs a second way out in case of fire, and that is typically provided by a window that is more than 44 inches from the floor. In a basement, you’ll typically need a window well that provides enough room for an exit.

Ceiling height codes vary, notes Schultz, but you generally need to follow the “rule of sevens,” which says that at least half of a finished attic must be 7 feet high or more, and that this area must be a minimum of 7 feet wide and 70 square feet. In basements, ceiling heights also must be at least 7 feet.

Make the space feel like home

Odds are you’ll need to do some work inside the walls or under the floors in order to create a functional space. In the basement, budget anywhere from $3,000 to $10,000 to resolve any dampness issues, and avoid using materials that moisture may damage, such as standard wallboard or carpeting. Garages and porches often have pitched floors designed to drain water, which may need to be leveled.

For better livability as well as energy savings, make sure to insulate any new space. “A fully insulated room sounds completely different than an uninsulated one and will feel more substantial,” says Schultz. Heating and cooling are also important considerations. For attics and basements, you’ll want a separate HVAC zone since the temperature dynamics are so different than in the main house. For garages, sheds and porches, you very likely will need new standalone HVAC systems.

Think about the future buyer

Whether you get a return on investment when you sell depends on a host of factors. But the numbers may be more favorable with a refinishing project than with an addition. According to the National Association of Realtors, a bathroom addition returns an estimated 63% of its $80,000 cost at resale in 2022. Converting a basement to a living area, on the other hand, returns an estimated 86% of its $57,500 cost. Of course, your return may suffer if you give up a more functional space like the garage, especially if on-street parking is scarce in your neighborhood.

To maximize your payback, says Schultz, remember that homebuyers want a house that is consistent throughout. Try to match the details in your new space with the rest of the house, or at least come close in terms of quality, style and color. That includes everything from flooring and molding to light fixtures and windows.

Also, to see a bump in your home’s value, you must get a permit for the project, which ensures that the contractor follows building codes and that the work is inspected by an independent expert. “An appraisal won’t factor in the space if it’s not permitted, because it still counts as unfinished space,” says Schultz.

If you’re considering a home equity line of credit to expand your home, estimate your rate and payments with this calculator.