At first it may seem like a distant idea: Who cares about prices in the coming decade when the more immediate issue is what's happening today? Since most owners aren't actually selling at this moment, 2015 or thereabouts represents the end-game for many of today's homeowners, the time when properties will be sold and profits will hopefully be pocketed.

The National Association of Home Builders has produced an interesting long-term study which suggests that "a slowdown in production and sales will occur over the next few years, largely in response to higher mortgage rates, but the number of homes constructed over the long-term ... will depend less on interest rates than on demographic trends and on the utilization of the existing housing stock."

Huh? Why are interest rates and population growth less important to long-term supply and demand than the way homes are used?

Here's why: Economists usually predict housing demand -- and thus prices -- on the basis of three factors:

• Changes in the number of households -- more households equal more demand. If local housing stocks do not expand sufficiently then prices can rise substantially.

• Changes in the number of vacant homes -- more vacancies suggest reduced demand, fewer vacancies mean higher prices and rents.

• Changes in "net removals" from the housing stock -- fewer properties to sell or rent raise the value of those properties that remain if demand is constant.

But what if we modified the way houses are used? What if we said the definition of a "household" is in flux?

All of a sudden traditional measures of real estate supply and demand would need to be re-thought. No less important, the type of housing stock most valued might shift from today's preferences to something different.

NAHB says we have a declining tide of "headship rates." Basically, this means that rather than forming a predictable number of households relative to the population, we have more adults living with their parents and more people living with siblings and other friends and relatives.

"While headship rate changes are not expected to have much effect on overall growth in the number of households," says NAHB, "changes in the population in each age group will produce large changes in the number of households, in the characteristics of households, and in the types of housing demanded."

In other words, as the baby-boom and post baby-boom generations age their housing needs will evolve. However, the change that's anticipated is not what you'd expect based on traditional levels of household formation. If NAHB is right, we're going to see more inter-generational households and more households with more adults.

So, what does all of this mean when you sell at some point in the future?

After looking at such factors as demographics, housing demand, labor force participation and mortgage rates, NAHB says builders are likely see "production levels over the next decade exceeding the average during the last decade. Indeed, the number of new conventional houses built during the decade from 2006 to 2015 will exceed the number produced in any previous decade.

"Considering the larger average size and more extensive equipment that will characterize the typical home built during the coming decade, the real value of residential construction during the next ten years will exceed previous decades by an even wider margin."

If builders believe the market will be at record levels in the coming decade that should be seen -- if correct -- as very good news for property owners because it suggests lots of real estate demand. In the same way that we now marvel at the low prices from 1997, we may look back in 2015 at the NAHB projections and think how great it would have been to buy in '06.

I hope NAHB is right. They surely make an interesting case. Alternatively, if we continue as a nation to spend $60 billion a month importing more than we export, if the federal government expends more than it takes in by hundreds of billions of dollars each year and if energy costs and supply cannot be controlled, then all bets are off because mortgage interest levels could ultimately climb to levels unseen since 1980 -- a year when the prime rate topped 21 percent.

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