When he looks at 30 years worth of numbers, this is some of what Gopal Ahluwalia, vice president of research at the National Association of Home Builders, sees:

* More single buyers in the new-home market.

* Smaller families than there were 30 years ago.

* Men and women delaying marriage longer.

"In 1970, 87 percent of the U.S. population was white," said Ahluwalia, who works at the trade group's Washington headquarters. "In 2000, it was 75 percent, with Hispanics now the second-largest group."

By just ticking off a representative sample of what he knows, Ahluwalia can point the nation's residential builders toward their customers, both present and future.

For example, the number of two-income families has increased substantially over the past 30 years.

"The income of females has increased in relation to males, from 45 percent of what males typically earned 30 years ago to 72 percent today," he said.

Rising salaries for women, married or not, have changed the composition of the real estate market. In 1999, the last year for which there are figures, twice as many single women as single men bought houses, according to the National Association of Realtors.

Single women accounted for 18 percent of all home buyers, which means 1.17 million single women purchased homes in 1999. In 1989, 606,000 single women acquired houses, representing only 13 percent of all home buyers, the group said.

Income for all wage earners has risen only 7 percent over 30 years, adjusted for inflation. For two-paycheck families, it has increased 50 percent over three decades.

At the same time, household size has declined for the past 30 years, "which continues a trend that began 50 and 60 years ago," Ahluwalia said. In the past 30 years, average household size has dropped to 2.58 from 3.35, and "we should expect further declines."

Yet as family size has decreased almost 25 percent over 30 years, the size of new houses has increased about 50 percent, to slightly more than 2,300 square feet.

In the early 1970s, two-thirds of all new homes were 1,500 square feet or less. Now, two-thirds are larger than 1,500, with homes 3,000 square feet or larger now 19 percent of the total.

Only 17 percent of the houses built 30 years ago had two stories. These days, more than 50 percent do.

Two-story houses allow builders to incorporate the features demanded by buyers as lot prices skyrocket and the amount of buildable land declines.

More than half of new houses have 21/2 bathrooms. Almost every house has a fireplace, even upscale houses in Southern California, where they are "used only three days a year," Ahluwalia said. "But you can't sell a house without one."

About 86 percent of new houses have central air conditioning, compared with 33 percent 30 years ago. Ahluwalia does not expect the percentage to go much higher, because "there are still areas of the country where central air conditioning isn't needed."

Houses, of course, have become more expensive and have more features than ever, he said, thanks primarily to the added buying power of two paychecks.

In the past 23 years, average new-home prices have more than tripled, to $240,000 in 2003 from $72,400 in 1980. Existing-home prices have almost tripled, to $214,000 in 2003 from $72,800 in 1980.

Sales of new and existing houses have doubled in 20 years.

The number of first-time home buyers in the new-home market has both short-term and long-term effects on the entire residential housing market.

"The percentages tend to fluctuate greatly," Ahluwalia said. For example, first-time buyers now make up 26 percent of the market. In 1988, at the end of the real estate boom of the mid-1980s, it was 32 percent.

In 1980, when interest rates were closing in on 18 percent, first-timers made up 48 percent of home buyers.

First-time buyers typically are found in the existing-home market, where prices tend to be lower. In addition, immigration is boosting the number of first-time buyers, and the majority of newcomers tend to live and buy in older cities where the housing also is older.

Some statistics have surprised him, Ahluwalia said. For example, more than 90 percent of new houses are built on site in the traditional "stick-built" method.

"Modular and panelized construction has remained consistent, even though we assumed that during periods when there were labor shortages, there would be an increase in the share of factory-built houses," he said.

So what does Ahluwalia know about today that will affect the future?

Early this year, at the International Builders' Show, Ahluwalia talked about the results of the National Family Opinion survey done in phases in 2000 for the National Association of Home Builders.

In the first phase, about 40,000 households were asked whether they had bought new homes during the past two years or planned to buy new homes during the next two years.

About 3,000 households that said they were planning to buy, or had bought, new homes were mailed the detailed survey. A total of 2,017 responses were received in that second phase.

The results showed preferences for:

* Larger houses with lots of space, including large kitchens next to family rooms. Homeowners want the two rooms to be visually open, or divided with a half-wall.

* Upscale features such as high ceilings and island work areas in the kitchen.

* Houses with front porches, rear decks or patios, and exterior lighting.

* Laundry rooms and dining rooms, which were considered essentials.

Some features that typical home buyers now want used to be optional and were standard only in upscale houses, Ahluwalia said. Today, the difference between average and upscale is that upscale houses are larger, with top-of-the-line equipment and materials.

Some features of new homes have improved so much that consumers are generally satisfied. For example, though consumers want large kitchens, most do not want to see the kitchens expand further at the expense of other spaces.

Among kitchen features, buyers favor walk-in pantries, island work areas and lighter-wood cabinets.

Only one-third of all buyers, however, say that new houses come with enough storage space.

Although there are regional variations, especially in the northeastern part of the country, many home buyers say they do not believe a separate living room is necessary.

About 25 percent of prospective buyers want a three-car garage, even if they have only one car and even if that would add considerably to the price of a house. Most would settle for a two-car garage.

Although survey respondents said they would be willing to pay for their favorite amenities, they were willing to spend only $5,000 upfront to save $1,000 a year in utility costs.

In addition, few of the respondents were willing to pay extra for a house built in a more environmentally friendly way.

Families may be smaller, but they want more floor space, NAHB economist Gopal Ahluwalia says.