Buying a house is just the beginning. Before long, you'll be repairing it, too. Fortunately, many building components— foundation, framing, plumbing and wiring— should last 50 years or more. But mechanical systems, appliances and surfaces exposed to the weather will not last nearly that long, even under the best of circumstances. "The reality of it is that stuff happens," says John Ghent, president-elect of the American Society of Home Inspectors and co-owner of a Trumbull, Connecticut, home inspection company. The older the house, the more maintenance it usually needs. "Experience shows that the average house may need a 50 percent replacement over a period of 30 years," says a handbook Ghent gives to home buyers. In each of the first 10 years after construction, a $100,000 house will require $750, or 0.75 percent of its value, in maintenance, according to Ghent. That rises to 1.5 percent per year for the next 10 years and reaches 3 percent per year in the third 10-year period. Predicted life spans are published for everything from microwaves to garage-door openers. Although these estimates are helpful, they are not intended to be exact, and your own experience will likely reflect that. Ghent, for example, recently inspected a house built in 1926 that still had its original boiler. Designed for coal, the boiler had been converted once to burn oil and a second time so it could run on gas. It's still in great shape even though it has more than doubled industry estimates for longevity. Maintenance history is one important variable, but so is chance. "Some things don't break," says Ghent, "and some things do." Budgeting for repairs involves location as well as luck. The same roofing job might cost 40 percent more in New England than in the rural South, for example, because of prevailing labor rates and other local factors. Bottom line: Take national repair estimates as averages that you probably will have to adjust for your area.