It is very small, just 1,500 square feet. Yet this ''idea'' house demonstrated to those attending the recent National Association of Home Builders convention here that such compact space could ingeniously include three bedrooms , 2 1/2 baths, a utility room, and an all-purpose first-floor ''great room'' that combines kitchen, dining, living, and family room functions.
It demonstrated, too, that architect-designed housing can be affordable. Chicago architect Larry Booth of Booth/Hansen & Associates designed the house, and Village Builders in the Houston suburb of Kingwood constructed it to sell for about $80,000.
''Architects are responding increasingly to the challenges and opportunities of residential design,'' George M. Notter Jr., president of the American Institute of Architects, told builders gathered here. ''As recently as 10 years ago, only 5 percent of all houses built in this nation were architect-designed. Today the national figure is up to 15 percent and growing. In some urban areas the percentage of architect-designed housing ranges from 50 up to 75 percent,'' he said.
The idea house was designed specifically as a first house for young couples in the 25-to-34 age range, with room enough for one or two children.
Research showed that this young family would likely have two incomes at the outset, with both husband and wife working. And there would be an expectation of upgrading later to a larger house as incomes, family size, and social responsibilities increased.
For many couples such a small dwelling would prove to be a ''transitional'' house, but it would satisfy their initial desire for a single-family house on its own lot, with trees, shrubs, flowers, and outdoor decks to enhance and enlarge living spaces, plus a detached two-car garage.
Because of prevailing high costs of land, labor, and materials, the architect determined that the design of the house would be straightforward and practical. In its comfortable simplicity, it would hark back to traditional Early American roots, with clapboard siding, chimney, and steep pitched roof. But in its modern-day efficiency it would incorporate the latest and most energy-efficient building materials and appliances on the market today.
To make the house appear from the street to be much larger than it is, the architect continued the slope of the roofline to extend the front facade beyond the outside edge of the house by 12 feet on each side. The false facade gives the house more presence and provides more side yard privacy. ''If you have to live in a little box,'' the architect contends, ''at least let it have some transforming quality.'' For that reason, he also did not make windows of uniform size, and their placement appears to be random.
On the first floor he allowed for 10-foot ceilings, a corner fireplace, a tiny entry, utility room, powder room, and a kitchen that enables the cook to enjoy guests in the main living area.
Touches of luxury upstairs include a hall lined with recessed bookshelves, a walk-in closet off the master bedroom, and a spacious master bathroom that includes a huge whirlpool tub, a separate shower enclosure, and two pedestal lavatories.
Decoration by Gary Crain, a New York interior designer, presented other surprises. Instead of the usual light backgrounds used in small rooms, Mr. Crain changed the pace by choosing a deep, rich blue-green for all downstairs walls, contrasting white woodwork, and a floral chintz on white background for windows and upholstery covers.
For the master bedroom he chose a soft, rich red, which provides a warm background for the bleached finish of the reproductions of Early American furniture and the patterns of handmade quilts and throws.
His biggest decorating challenge in the house, Mr. Crain says, was making the two 8-by-8-foot children's bedrooms appear as uncluttered as possible. With deep piles of pillows, he converted each single bed into a daybed for daytime reading and lounging.
To make the most of every inch of space in a small house, Mr. Crain suggests the following:
* Don't use underscaled furniture. Rather than downscaling pieces, use furniture of normal size, but less of it.
* Do not use overscaled sofas, even to serve as focal points. Standard lengths are best. Modular seating is great in small spaces because it can be arranged and rearranged and moved easily to a new location.
* Place furniture on an angle if it agrees with the architecture of the house. In this house, a corner fireplace inspired the architects to place a sofa , two chairs, and a coffee table squarely in front of it, but at a diagonal in the room.
* Whatever flooring you select, use it throughout. This house features white ceramic tile for the downstairs and wall-to-wall carpeting for the upstairs. Rag area rugs on the white tile designate various living areas.
* To keep a sense of spaciousness, don't have too many little things around, such as little tables, little lamps, and other accessories.
The idea house was sponsored by the National Council of the Housing Industry, the Builder (official magazine of the National Association of Home Builders), and Good Housekeeping magazine. Its purpose was to demonstrate innovative design , new building products, and cost-saving construction techniques. For instance, the switch from standard 16-inch to new 24-inch center framing, plus the use of metal drywall clips for corners and partition intersections (instead of backup studs), reduced the amount of lumber in the house by 25 percent.