The saying "They don't build in 'em like they used to" is particularly true of today's new housing. a major reason: timber products are changing. The change starts with the trees themselves.

The vast timberlands of the West, logged for over a century, are becoming more and more second growth. Increasingly, trees now being cut are smaller-diameter specimens grown in managed forecasts. And costs have climbed, forcing the lumber industry to use wood fiber more efficiently.

In housing, new wood products and lumber-efficient design are the result. This shows in the quantity of lumber going into a new house: In 1950, it averged about 10,800 board feet. Today, the average house is almost twice as large (about 1,700 square feet), but it uses nearly the same amount--about 11,200 board feet.

Look at beams an trusses. Since there aren't many large-diameter trees left to make into big beams, glue-laminated ones--made of lumber glued together under pressure--have been developed. Similar in function are lightweight woven I-beams, which have a slender center section of plywood and outer edges of narrow, laminated veneers. "Each tree goes 2-1/2 times further as an I-beam than as a 2 by 10," says one spokesman. And today's ready-made wood roof trusses, employed in about 95 percent of new housing, use small-dimension wood (2 by 4's or 2 by 6's) joined with metal plates to create an engineered roof support.

This truss technology is extending to floor trusses and even to truss-framed houses, in which roof, floor, and wall sections are connected into modules that arrive at the building site stacked on a truck. …