Two Washington area builders are incorporating into their new homes passive solar features that utilize solariums or greenhouses.

The Cumberland Corp., based in Manasas and with a manufacturing plant for its custom package homes in White Post, Va., is introducing a Solartrak series of homes after five years of research, said John E. Folds, president. Using what is called an envelope design, the house has glass panels in the roof on a southern exposure to capture sun heat and circulate it through a solarium and a 30-inch air space around the house.

In the summer, a screen covers the glass section of the roof and a section of the roof is opened to enable a fan to withdraw hot air from the perimeter of the house. The contemporary Cumberland house also has six-inch walls with thermoply sub sheathing, heavy roofs, insulated glass and a double-entry "air-lock" vestibule entry.

A Solartrak Cumberland house will be shown Sunday, Aug. 16, at 2182 Lake Dr. Pasadena, Md., near Annapolis, and exact directions may be obtained by calling 261-2020. Another Solartrak house will be shown Sunday, Aug. 23 at 5820 Hallowing Dr., Lorton, Va., with directions available by calling 471-6111.

Folds said Cumberland has been manufacturing and building custom precut houses for 12 years and that most have been built in this area. The firm built and sold 125 houses last year in a price range (excluding lot) of $85,000 to $125,000.

Contemporary Dwellings Inc., another area home-building firm, is completing its first model in a 10-lot subdivision of passive solar homes called Jefferson Estates, near Arnold, Md. The houses will have tiled solar greenhouses to capture heat to be circulated through the house by convection. The houses also will have fireplaces and wood stoves.

Ron Shriner of Giddings and Associates Inc./Better Homes and Gardens, is handling sales of the two-story, three-bedroom dwellings, priced from $91,000. The site is on Mago Vista Road in Anne Arundel County. The first model house is scheduled to be completed in late August. Interested persons may arrange a viewing by calling (301) 954-0410.