Houses averaging $100,000? The day may not be far away

How long before the average price of a house in the United States reaches $ 100,000? ''Maybe within the next two years,'' predicts Michael Sumichrast, chief economist of the National Association of Home Builders (NAHB). Today the average price is around $82,000, while the median is $74,000.

''It may take five years for the median price to get up to $100,000, according to Mr. Sumichrast. ''But I'm not too sure in even five years,'' he demurs.

One thing is quite sure, according to Sumichrast: Inflation is expected to remain low for the next few years. ''If this is true, then we won't see this crazy appreciation of housing prices which we've had.

''A house in Georgetown (a section of Washington, D.C.) selling for $250,000, which sold 10 years ago for $30,000 - I don't expect this sort of thing to go on.''

The NAHB economist sees a nationwide price rise of 5 to 7 percent in 1983.

Meanwhile, Sumichrast asserts:

* The fixed-rate mortgage, that old standby that put millions of Americans into their own homes in the last 30 to 35 years, has survived the recessionary crunch and now is finding renewed popularity among lenders, even though rates are edging back up.

Money is readily available ''and lenders are looking for places to put their money,'' Sumichrast says.

Close to 90 percent of all residential mortgages today carry a fixed rate, whereas a year ago it was about 30 percent. Thus, he adds, the fixed-rate mortgage is very much alive, but ''whether it will continue this way depends on the market.

''The fixed-rate mortgage - 20, 25, and 30 years - is going to remain as long as we have some hope that the financial markets are going to remain fairly stable.''

* The detached, single-family house is still the choice of most home buyers, a fact that isn't likely to change soon.

''People prefer their own piece of ground,'' says the builder-economist.

''Condominiums have problems with fees, associations, et cetera,'' he adds, ''and will never capture a major share of the housing market. Condos are expected to account for no more than 8 to 10 percent of the total market in the foreseeable future.

''But compared with almost nothing 10 to 15 years ago, that's not bad,'' Sumichrast muses.

Savings and loan associations now have a record inflow of funds, something they never had before. ''And they don't know what to do with the money,'' the economist asserts. ''This is a major problem today. I also think the pension and retirement fund money will be the future for residential mortgages.''

S&Ls right now are becoming a ''handshake,'' just the way mortgage bankers were for years. They lend money for the mortgage and then sell the mortgage in the secondary mortgage market, which, in turn, is bought by pension and retirement funds looking for a good deal.

''Mortgages are a very good deal,'' Sumi-chrast asserts.

The average length of a home mortgage today is about 28 years, but this will probably shorten.

Looking ahead, the economist predicts a booming housing market in the next decade, ''provided we can supply mortgage money at a reasonable rate.'' Then he sees the bottom again dropping out of housing demand. The number of people between 25 and 38 in the next decade will be 16 million, compared with 11 million in the last decade.

And what will the houses look like in the next 10 or 15 years?

For one thing, they'll be smaller. The major impact of the housing downturn over the last few years has been smaller units because of the sharp rise in the price of housing as well as money. Too, the energy-efficient house today is the result of the skyrocketing rise in the cost of energy.

''You can't sell anything that isn't energy-efficient these days,'' says Sumichrast.

The major architectural change is the openness of the units today. Even a small house will often give the impression of a much larger house because of fewer partitions, chimneys that may run up two stories, the addition of an entry hall, etc. Simply, there are fewer cubicles in new housing.

''This is the new design of the early 1980's,'' Sumichrast says.

Some builders now provide ''computer rooms'' in new housing, including the prewiring. This, however, is usually seen as more gimmicky than a permanent change - anything to get the eye of a prospective house buyer. If it's different , people will take a look. This seems to be the builders' approach.

Fireplaces are coming back in a big way, even in the South.

Builders are also getting back to European-type windows, such as casements, which are very well insulated. European-type doorknobs are coming on strong, including a handle you push instead of twisting a knob.

Sumichrast says that four-inch kick moldings are making a comeback, ''as well as crown moldings or a type of gingerbread around the top of rooms - the kind of thing done in the 1920s and '30s.''

Kitchens are much more open and are often combined with dining space.

The greenhouse-type of passive solar heating is appearing everywhere. In other words, houses are sited to capture the sun in the most effective way. North-side windows are eliminated, if possible.

What is not doing too well is active solar installations, probably because of the cost.

Active solar had a spurt in the mid- to late 1970s. When analyzed a few years later, however, even with government grants, the payback just wasn't there.

''Solar cells are still 10 years in the future,'' Sumichrast concludes, ''but passive solar is sprouting all over.''