Old houses are old because they were well designed and built with quality, hand-hewn materials. Maintaining these parts is not especially difficult or expensive. Restoring or replacing them once they've been neglected is.

Old houses demand owners with a marathon mindset: investments in in-kind repairs are often long term, sometimes exceeding the owners' expected occupation of the house. A new slate roof, for example, will cost four times more than asphalt, but it will last four times as long: one hundred years.

Old houses are not custom. You adjust to live in them; they cannot be changed to accommodate you without destroying the very qualities that attracted you in the first place. In that sense, old-house ownership is a lot like marriage, observes Alna restoration contractor Les Fossel. "When we buy an old house, we think the way to possess it is to spend money on it," he says. "Resist that temptation. Be very cautious because presumably you bought this building for the same reason you married your spouse: they are different than you. Often they're better than your dreams. So give them a chance before trying to change them. Cherish the differences. Being rational is one of the hardest things to do with the things we love, but we must. Your home is the largest investment you make. It makes sense to apply logic to it."

In that spirit we offer some do's and don'ts for a successful relationship with your old house.

Do nothing. Few sights make Noelle Lord cringe more than that of a dumpster in the driveway of a recently sold old house. "It drives me crazy," says Lord, a restoration consultant and plaster specialist from Limington. "It gives me a pit in my stomach." She wonders what the new owners are demolishing and why. "People need to remember why they bought an old house in the first place. Live in it for a while and slow down. Appreciate its historic qualities. Don't jump in and start ripping and tearing because you will be sorry, and the future owners will be even sorrier."

This is not merely a purist's biased opinion. It is sound economic advice, according to Fossel, who approaches antique homes with commonsense Yankee frugality. "Here you have a building that has worked for 150 to 200 years and suddenly you come along and want to change it," Fossel says. "Ask yourself how little can you do to accomplish your goals. There will always be people trying to get you to spend money to solve problems. Find out whether the proposed solution solves anything. Follow the logic trail. If it comes to a dead end, don't do it."

Don't do windows. By all means, wash them. Just don't remove them, as the Sirens of the vinyl replacement window industry entice with promises of energy efficiency. With their limited sizes, pane configurations, and colors, vinyl replacements almost always look out of place on an old home, and they never match the originals' handcrafted details. Moreover, says window restorer Marc Bagala of Portland, replacing wooden windows with vinyl ones is like, well, throwing money out the window.

Studies have shown that the seals between vinyl frameworks and insulated glazing typically fail within seven to twenty years. It, as well as other parts, cannot be repaired; time for another replacement. By contrast, double-hung wooden windows, with their ingeniously simple weight-and-balance systems, have a long performance record. "Your windows have lasted a hundred years," Bagala says. "With a little TLC, they might last another hundred years. To replace them with something that won't last twenty years is like putting Mag wheels on a Model T."

Which is not to say that vintage windows don't need attention. They do, sometimes lots of it. "For some reason, window maintenance is always deferred," Bagala says. "When the roof leaks, you have to do the work. When the window doesn't work well, you just don't open the window." He frequently hears from homebuyers who have just moved in and discovered their windows won't open (in one case, all thirty-five of them). The cause is typically mundane (the upper sashes have been painted in place) and easily corrected (scrape away the excess paint).

Wooden windows are rarely beyond repair, even when parts of the frame or sash are rotted. Do-it-yourselfers can fix them; others rely on experts. "A long-term solution does cost more than a $150 replacement window," Bagala acknowledges, "but if you install high-end replacement windows, the cost (about a thousand dollars per window) — and the maintenance requirements — are about the same as restoration."

Don't be "fuelish." Old houses' reputation for draftiness makes their owners especially susceptible to sales pitches for expensive energy-efficient products. But do you really have a heating problem? Fossel tells of a Rockland woman who was spending six hundred dollars a year to heat her small antique Cape. A housing assistance program offered an interest-free loan to install vinyl replacement windows and siding to improve the home's energy efficiency. "It didn't make sense. She wasn't going to save money on a six hundred dollar heating bill. So look at what you're spending: if it's costing you $2,500 a year to heat a two-story building, you're probably in pretty good shape."

As for those historic windows, weather stripping and good storm windows will make them as efficient as the short-lived replacements, Fossel says. Remember, too, the logic trail: "In the average house, heat is lost through the roof, not the windows. Heat rises. It's basic science. Twelve inches of fiberglass insulation in the attic — R-38 insulation — is a good thing."

Blown-in insulation, a fine product for new construction, generally does not perform well in the quirky wall cavities of old houses. "It ends up being very inconsistent in the way it settles," Lord warns. "Moisture gets trapped and you get rotting timbers. Also, because it settles, it's not insulating upstairs where you need it most."

Don't fix symptoms; fix causes. "There's a good reason to put vinyl siding on your house: you probably won't have to paint it, ever," Fossel says. "But if you're doing it because your paint is peeling, it's probably because moisture is collecting behind the clapboards. You don't have a paint problem. You have a moisture problem. We don't solve a problem by hiding it. You might even make it worse. So carefully define the problem you want to fix and make sure you're looking at the problem and not a symptom." Moisture is the single biggest havoc wreaker in old houses, yet keeping it out, whether by repairing leaks or changing the grade around the house, is often the cheapest repair a homeowner can make.

Another example: damaged plaster is rarely a sign of a plaster problem. "Plaster doesn't just decide to fail," Lord says. "We have 250-year-old horsehair plaster that is still going strong. It has tremendous longevity." Frequently, homeowners tear down chipping and peeling ceilings when a little elbow grease — okay, a lot of elbow grease — would remove the calcamite paint that is the culprit. Likewise, plaster cracks not because it's old or poor quality, but because the house has moved, perhaps due to natural settling or to something else, like rotting posts and sills.

Also, beware of problems that aren't problems. "People hate hairline cracks in their walls," Lord says, "but we pretty much leave them alone. In summer they disappear when the building swells."

Repairing plaster rarely costs more than replacing it with drywall, which is less sturdy and less flame retardant, offers less soundproofing, and lacks plaster's hand-troweled texture and depth. "The majority of the surface square footage of your house is plaster," Lord points out. "If you take it away, you lose a lot of the aesthetic."

Do resist trends. Old houses are often perceived as expensive because of the owners' lifestyle demands. "I have four brothers," Fossel says. "Growing up, we had one-and-a-half bathrooms and we were fine with that. We were deprived by today's standards. Now people need a bedroom for each child and nothing less than two-and-a-half baths. Make sure you're not being talked into standards that exceed your needs. Do you really need two sinks in the bathroom? How often are you and your husband washing your hands at the same time? Do you really need a $36,000 kitchen with granite countertops? If the kitchen is really the center of your family life and you really like to cook, maybe it makes sense. Ask yourself, 'How else could I spend this money?' "

Do have a maintenance plan. "Treat your house's systems like you do a lot of things in life, such as your car," says Victor Wright, a copper and slate roofing specialist from Waterboro. "You know you've got to care for it, or it's going to fail."

Different house parts have different requirements, but there is no question that a little regular attention can prevent major and costly work down the road. For roofs, Wright recommends a yearly visual inspection — look for cracks in the gutter seams and missing or misaligned pieces of roof slate. For windows, Bagala suggests a thorough inspection every five years. "When you see chipped and cracked paint, repair it," he says. (Just don't paint in the sashes!)

When there is work to be done, seek tradespeople who know and respect old houses. Many vintage interiors have been damaged in the course of plumbing and electrical upgrades because contractors schooled in new construction believed wrongly that they had to gut the house to do the work. "Tradespeople who 'get' old houses will be patient," Lord says. "They'll take the time. They will cost more, but I'm not convinced that it really is more once you consider the alternative, with the costs of demolition and disposal and recreating whatever you lost."