You've vowed that you'll never move again. Then you shouldn't think about improvement as an investment in anything but your happiness. Some of the most fulfilling additions are those that refund the least.

Tops in this category is a master bedroom suite. A 24-by-16-foot bedroom with extras like a walk-in closet, a whirlpool tub, and a dressing area can cost as much as $100,000. The day your builder drives in the last nail, your new bedroom is only worth about 69 percent of that amount. So what? You can't put a price on a good night's sleep. (For the record, though, it's more reasonable than even what the short-term homeowner pays for his bathroom: Amortize the lost $31,000 over 30 years and you'll find your new sleeping quarters cost less than $3 a night.) Add a sunroom and kiss 41 percent of almost $70,000 goodbye forever. But think of all the pleasant days you'll spend in those rooms: priceless.

If that kind of indulgence is too much for your financial ethics, consider that renovations can save money in other ways. A 20-by-30-foot basement entertainment room with a wet bar and a 5-by-8-foot full bath can cost $60,000 and up. Sure, only 75 percent of that goes into your bottom line, but entertaining at home means filling your gas tank less often. We built a theater room in our home, and now every Friday is a low-cost family movie night.

No matter how long you expect to be in your home, first figure out what you can truly afford. Borrowing for any of these projects seriously subtracts from your rate of return, not to mention your enjoyment of your new addition. The last thing you want is for financial concerns to spoil those precious moments that make your house a home—like the first bite of a perfectly grilled hamburger.

Michelle Singletary is a nationally syndicated finance columnist for The Washington Post.