Peek under floor, beneath paint, may reveal more than Colonial charm

Houses talk. Sometimes they even shriek. At least they do to Ron Passaro and his colleagues in the American Society of Home Inspectors. Take the case a few years ago of the old and outwardly beautiful colonial in Westport, Conn. A couple, eager to buy the $200,000-plus home, had the forethought to hire a home inspector before making the final offer. The inspector found the house to be everything it appeared to be - until he wormed his way into some of the more inaccessible crawl spaces. There he found standing water, six inches deep in parts, and rot, lots of it. In places the sills had turned to something resembling a black ooze.

The house had ''serious problems,'' a still mud-smeared inspector told the would-be buyers. Even so, they were reluctant to believe his report and called for a second opinion, which confirmed the problem. As a result, the sale was renegotiated, and the couple bought the home (virtually every house can be repaired) for some $30,000 less than they were originally prepared to offer.

The message from this example, and countless others like it, is clear: Don't allow only the aesthetics, charm, and character of a house - older homes particularly - to influence your purchase. This isn't to suggest that much cannot be learned from the outward appearance. But for an accurate picture of its condition and expected lifespan you must look beneath the paint, behind the wallpaper, and under the floors as well.

A home is likely to be your single largest investment. Protecting it with a professional inspection makes obvious sense. That service now is available nationwide from members of the relatively new but soundly established American Association of Home Inspectors (ASHI).

As recently as a decade ago the society didn't exist. Then it was largely ''buyer beware'' when a house was bought. The court cases that resulted when buyers weren't careful did more for the lawyers involved than the homeowners themselves. A need obviously existed and individuals from varying industry-related professions - carpenters, plumbers, architects, and the like - began offering the service on their own. Mr. Passaro was one of them.

A home builder by profession, Passaro got into the home-inspection business on request, so to speak, some 14 years ago. Friends and aquaintances, contemplating the purchase of a house, would ask him to look it over.

''We would walk over the place together,'' Passaro recalls, ''and I would comment on what I saw. Afterward, I'd give my overall opinion on the place, I'd be given a fee, and that would be that. There was no written report and no standards for me to go by. I'd simply give an opinion based on my experience as a builder.''

For years, Passaro thought that perhaps he was the only one in this business. Then one day he decided to check out the Yellow Pages of various New England phone books. Under ''Building Inspections,'' he found several others who offered the same service.

A few telephone calls brought them all together, and the New England Society of Home Inspectors was formed in 1976. Soon others outside the six-state region heard about it and asked to join. Within a few months the society became national, and even international. Today there are some 300 members in 44 states and a handful of associate members from Britain, one of whom flies out every year to attend the society's annual meeting and seminars.

''Our members thirst for knowledge,'' says Passaro. ''We're already a pretty efficient group and we're getting more proficient all the time because of the continual exchange of information at seminars and other educational opportunities which we provide to our members.''

Indeed, a member must upgrade his knowledge every year to retain membership in the society.

Now the society has a set of basic standards that apply to every home inspection. This, then, is what an ASHI member will look at for you when you seek his services:

* Structural integrity of the home. In other words, he will see that the timbers are sound and free from rot or insect damage. He will also check that the timbers are adequate to support the load. Many older homes were overbuilt (stronger than necessary), but some went the other way.

If the china rattles in the cabinet every time you walk across the dining-room floor, then you know that more support is needed. In some cases, additions by former owners might have compromised the basic strength of a home. ''We check all of this,'' Passaro says.

* Plumbing. The state of the pipes are checked along with the type of material used. If there is any galvanized piping left in the system it has probably already outlived its life expectancy ''because galvanized pipes have rarely been installed in the United States since well before World War II,'' according to Passaro. Even brass pipes are suspect for they indicate a 40 -year-old system.

* Electrical service. Is it adequate for the house? Was the wiring properly done and is it still in good shape?

* Heating system. The inspector will check its operation and distribution.

Among other numerous items checked are the soundness of the roof and walls and the amount of insulation they contain.

When the inspection is complete, the inspector can tell the buyer that he has a little maintainance work to do, some repair work here and there, or perhaps that an entire sytem needs replacing. As Passaro puts it: ''We put the house into perspective for the buyer. He knows after we are through whether he can afford the house or not. Remember, if a house is priced at $100,000 and we find

''He can now decide whether the house is worth that much or whether he should ask for a $10,000 cut in price.''

On average, a home inspection costs one-tenth of 1 percent of the purchase price of the house. The inspection charge on a $200,000 house should cost about

To find a home inspector in your area, check the Yellow Pages of your phone directory under ''Building Inspections.'' You also can write to ASHI, Suite 520, 1629 K Street NW, Washington, D.C. 20006.