With Americans relying on the equity in their homes as an essential element of their life savings, most mortgage lenders want home owners to better understand how to preserve value in their most important financial asset.

A recent study sponsored by Bank of America and conducted by our national affiliate, National Association of Home Builders, provides some general guideline information on how many years of service a home owner can reasonably expect from the various components of a home. The study is based on averages, therefore the longevity of a product or component of the house can be impacted by how we use the product, maintenance, climate, advances in technology and simple consumer preferences.

Some home components are expected to last the life of the house. Among them are toilets, wood floors, all types of insulation, and fiberglass, steel and wood exterior doors. On the other hand, some components have a much shorter life expectancy. Wood decks should last about 20 years, depending on climate, and kitchen faucets should last about 15 years. Linoleum floors have a life expectancy of about 25 years, and furnaces can be expected to last 15 to 20 years.

Because we like to make changes on a frequent basis, many items get replaced long before the end of their expected life. For example, the practical life expectancy of kitchen cabinets is about 50 years. However, many people buying a 15 or 20 year old house would make installing new, updated kitchen cabinets a priority. Likewise, some home owners paint their homes every year or two, even though interior paint has a practical life expectancy of about 15 years.

The study found that of the major appliances in a home, gas ranges have the longest life expectancy, at 15 years. Dryers and refrigerators last about 13 years. Appliances with the shortest life spans are: compactors (six years), dishwashers (nine years) and microwave ovens (nine years). Some appliances don't meet their life expectancy, however, because changes in styling, technology and consumer preferences may make newer products more desirable. Also, how long they last depends on how much they are used.

Kitchen cabinets are expected to last up to 50 years, medicine cabinets for more than 20 years and garage/laundry cabinets for 100 years or more. Closet shelves can last a lifetime.

Masonry is one of the most durable components of the home. Chimneys, fireplaces and brick veneers can last a lifetime, and brick walls have an average life expectancy of more than 100 years.

Natural stone and concrete countertops, which are less expensive than a few years ago, are gaining in popularity and can last a lifetime. Cultured marble, by contrast, is relatively short-lived, with an age expectancy of 20 years.

Exterior fiberglass, steel and wood doors will last as long as the house stands, while vinyl and screen doors have life expectancies of 20 to 40 years, respectively. Closet doors are expected to last a lifetime, French doors for 30 to 50 years. Garage doors last 10 to 15 years, and light inserts for 20.

Timber frame houses and structural insulated panels will all last a lifetime, as will wall panels and roof and floor trusses. Softwood, hardboard and plywood average 30 years, while OSB and particleboard last twice as long.

Kitchen sinks made of modified acrylic will last 50 years, faucets will work properly for about 15. Bathroom shower enclosures can stick around for 50 years, although the shower doors could be in a serious state of decline in about 20 years. Showerheads last a lifetime, as will toilets, although tank components require some maintenance. The durability of whirlpool tubs can run from 20 to 50 years, depending on use.

Poured as well as concrete block footings and foundations last a lifetime, assuming they were properly built. Waterproofing with bituminous coating can start to spring leaks in 10 years, unless it cracks, in which case mortal damage is immediate.

Heating, ventilation, and air conditioning systems need proper and regular maintenance in order to work, but even when they are pampered most of their components last only 15 to 25 years. Furnaces live for 15 to 20 years, heat pumps for 16 and air conditioning 10 to 15. An electric or gas water heater has a life expectancy of about 10 years. Thermostats usually are replaced before the end of their 35-year life span because of technological improvements.

Cellulose, fiberglass and foam used in insulation materials will last a lifetime provided that they are not punctured, cut or burned; are kept dry; and are not subjected to UV rays.

On the outside of the house, slate, copper and clay/concrete roofs have a 50-year life expectancy; asphalt-shingle roofs, 20 years; fiber cement shingles, 25 years; and wood shakes, 30 years. However, the life of a roof depends on local weather conditions, proper building and design, material quality and adequate maintenance. Brick, engineered wood, both natural and manufactured stone and fiber cement will last as long as the house. Exterior wood shutters are expected to last 20 years, depending on the weather. Gutters made of copper can last 50 years, of aluminum, 20.

While there are dozens of other structural and decorative components used in the average home, the bottom line is maintenance. Not allowing a problem to deteriorate into a disaster is key to how much time and money it will take to secure our investment.