(MONEY Magazine) – A $70,000 surprise. That's what my parents got this past fall, in the form of a termite infestation that ate away the inside of three interior walls from the basement to the third floor. "I'm shocked the bathtub didn't fall through the ceiling," the contractor told my folks. As Jeanne Salvatore of the Insurance Information Institute explained to me, this put them in a bad spot. Termites, along with birds, vermin, rodents and other insects, are never covered under a homeowners policy. But a bathtub that cratered due to a fire would have been.

Granted, this is an unusual example. Salvatore said she couldn't remember the last time she'd been asked about termites. But I've long believed that one of the biggest financial difficulties of being a homeowner is that while it's pretty simple to wrap your brain around your mortgage payment, taxes and insurance, the question of what it costs to actually live in your house is much more complicated. Now, a survey of 1,002 homeowners conducted for Sears Roebuck by Matthew Greenwald & Associates backs me up. It reports that half of all homeowners never estimate what it will cost to live in a house before buying it.

So whether you're thinking of buying, trading up or just trying to maintain the status quo, what should you do to avoid surprises in the future?

START WITH AN INSPECTION Of course you'll get an inspection if you're buying a new home. (My parents' house passed a termite inspection five years ago when they moved in.) You should walk through with the inspector--to find one, go to the website of the American Society of Home Inspectors at ashi.org--as he or she looks at all of the major systems in your home, from the roof to the appliances. You'll come out with a road map of what you'll need to replace or repair and a rough timetable for when the work will have to be done. Once you've been in the house 10 years, spending $500 or so for a repeat inspection will let you know what lies ahead.

BUDGET FOR MAINTENANCE According to Kermit Baker, senior research fellow at Harvard University's Joint Center for Housing Studies, you should plan on spending 1% of the value of your house (minus the value of the land) on annual maintenance. If you recently spent $400,000 on your house and it's sitting on a $100,000 lot, you're looking at $3,000 a year. But, notes former contractor Tim Carter, who runs the Ask thebuilder.com website, what you have to realize is that the number accrues. If you haven't put any money into your house for, say, five years, you can be pretty sure that a $15,000 maintenance bill is around the corner. That's why he suggests making regular deposits into a "sinking fund," an accountant's term for a pool of money you'll use for future expenses.

Mark Zandi, chief economist at Economy.com, notes that the cost of making household repairs has been outpacing inflation (often by as much as one-third) for the past five years. So raise the amount you're depositing into the sinking fund each year to keep pace with those increased costs and the rising value of your house. (For a look at some of the costs you may face and how much you need to sock away to cover them, see the table at left.)

DO IT NOW--AND DO IT RIGHT Letting a problem fester is likely to cost you significantly more in the long run. Take the urethane coating on your hardwood floors. Putting on a new coat once every 18 months will cost pennies a square foot. But if you wait until you've worn the coating down to the floor, then you have to sand the floor completely and apply four to five coats of urethane at a cost of dollars a square foot. Pay to have the job done right. There's nothing more frustrating than having to redo a shoddy job a year down the road. Well, maybe not nothing. You could have termites.