The Loudoun County Board of Supervisors this week added language to its new development plan for the area north of Dulles that is designed to stress the flexibility of that planning document.

The new language states that formulas showing what public facilities the county expects developers to pay for in return for winning approval for higher density development are only guidelines, not mandatory fee schedules.

Under Virginia law, counties cannot insist that developers help pay for county facilities such as schools, roads and recreational facilities that will be needed to provide services to a new development. Instead, counties negogiate voluntary contributions, called proffers, from developers.

The Dulles North Area Management Plan, which covers the 34-square-mile area northwest of Washington Dulles International Airport, suggests limiting residential development to a maximum of four houses on each developable acre. The guidelines laid out in the plan set up a sliding scale under which a developer can build up to 2.8 homes per acre without making major off-site improvements. But to achieve a higher density, a developer would be expected to contribute to "significant off-site road improvements which would be of countywide benefit" and to the county's farm preservation program, the plan says.

Developers wanting to build more than four homes per acre probably would need to seek an amendment to the plan unless the board decides that exceptionally generous proffers warranted a higher density, according to county attorney Edward Finnegan.

The new language in the plan was adopted on a 7-to-1 vote with county board Chairman Frank Raflo casting the lone dissenting vote. Raflo wanted to require that developers seeking more than four homes per acre go through the plan's amendment process.