Judging by the experiences of readers from around the country, some things don't last as long as we are led to believe.

That is the reason I've greeted the announcement of a study to determine the life expectancy of common household components with great interest.

The study was conducted by the National Association of Home Builders and financed by Bank of America Home Equity.

In the thousand or so years I've been writing about home-related products, I've interviewed scores of experts from product research and development departments, builders, remodelers, home center spokespeople and readers.

My conclusion: Your guess is as good as mine and theirs.

I interviewed the R&D expert from a faucet manufacturer, who predicted that his product would last 25 years, if warranty requirements were followed.

In response, I received letters from two owners of the company's faucets. Both complained that their faucets went in a few months, and that I was doing the public a disservice by "taking the maker's side," as one put it.

I handed the letters to the manufacturer, who followed up with both customers. In the first case, the complainer had installed the faucet "his way," instead of following the directions. In the second case, the faucet had indeed been faulty.

Both customers were taken care of, even the first. Most manufacturers, I've discovered, value their reputations.

I refer to the first as a complainer, because he couldn't have been less civil. The second customer was much better, but the manufacturer treated each equally.

Recently, a reader wrote in about his "lemon" refrigerator, which, after a year, still did not keep things cold, even after numerous visits by several repair people.

I forwarded that complaint to the manufacturer, who had it corrected in a week, and had promised that if the situation had not been resolved to the customer's satisfaction, the man would receive a refund with which to buy a new refrigerator from another maker.

The fix worked.

"For the first time in a year, the refrigerator is working as it should," he said, being as kind and patient as he had been in his first contact with me.

In the NAHB study, there is the caveat that actual life expectancy of a product has little bearing on consumer preferences, which might result in a product such as a kitchen counter being replaced long before the end of its useful life or a room being painted only once in 50 years.

Other factors that can have a significant effect on life expectancy include maintenance, proper installation, the level of use and the quality of the materials.

For example, all types of insulation can be expected to last a lifetime if they are properly installed and are not punctured, cut, burned or exposed to ultraviolet rays and are kept dry.

Windows, because they can be exposed to extreme weather conditions, have a much shorter life expectancy. The study, which polled experts in the various fields, found that aluminum windows can reasonably be expected to last 15 to 20 years and wooden windows can last upwards of 30 years.

Like windows, the life expectancy of a roof depends on local weather conditions as well as appropriate maintenance and quality of the materials. The study found that slate, copper and clay/concrete roofs can be expected to last more than 50 years. Roofs made of asphalt shingles should last for about 20 years; fiber cement shingles should last about 25 years, and wood shakes for about 30 years.

Although some avid decorators may repaint every six months, homes usually need to be painted every five to 10 years depending on the content of the paint (its glossiness), its exposure to moisture and traffic. Quality paints, per se, are expected to last 20 years or more.

They left out the most important ingredient in how long a paint job lasts. Surface preparation is the key, as my friends at the Rohm & Haas Paint Quality Institute have drummed into my head for these many years.

"It's important to remember that the life expectancies for materials included in this study are averages," said Gopal Ahluwalia, the NAHB's staff vice president for research who was the point person on this study. "Usage, weather and a number of other factors can influence life expectancy," Ahluwalia said.

"Moreover, homeowners often replace materials long before the end of their expected life span due to personal preferences and changing trends," he said.