Two-unit houses are being built to look like large, single-family houses in the Bayberry Woods section of Burke Centre. And they are selling.

William L. Berry, the builder, said that there are sales deposits on 18 of the houses, which are priced from $64,000 to $69,740. The first of the Fairfax County subdivision's duplexes should be ready in April, he said.

Two houses, side by side and sharing a common wall, are unusual in new construction here. Berry said that zoning in the Burke area made the duplex approach possible. The houses cost less than single-family units his firm is building, he said.

"The economies of construction with the common wall are small," Berry noted. "The major saving is in land cost. Individual houses are on lots averaging 4,600 square feet. Normally, a single house would be on a lot twice that large."

Architect Robert Kaplan designed the Bayberry Woods' duplexes to have entrances on opposite sites and to avoid the sameness look of older-style "double" or semi-detached houses. The duplexes are built in small clusters around cul de sacs. A parking space or a garage is provided for each house.

Other new duplex houses have been built in this area in recent years at Rossmoor, St. Charles in Charles County, Md., and by Stanley Martin Communities near Catholic University.