GREENFIELD — The town’s Planning Board voted Thursday night to approve a special permit for the first detached in-law apartment in town, on the condition that the homeowner planning to build the dwelling move the structure farther from her neighbors’ property line.

On Thursday, the board continued a public hearing from last month, during which neighbors raised concern about how the structure would impact their home. The Planning Board chose to delay its decision about whether to grant the special permit until this month to give the homeowner — Marcia Vincent — time to present a more detailed site plan, as well as to give the board time to clarify several questions.

On Thursday, after a nearly 3½-hour meeting, the Planning Board approved a special permit for the dwelling on the condition that Vincent build the structure 60 feet from the neighbors’ property line and plant 4-foot tall arborvitae for screening.

The Planning Board has also required that Vincent install downcast lighting along the 100-foot walkway to her cottage on poles no taller than 6 feet.

Less than a month after Town Council passed an ordinance legalizing accessory dwelling units in town, Vincent applied for the special permit to build a detached, 882-square-foot cottage on her 2.5 acres at 907 Bernardston Road. She said she could get extra income from renting out the cottage, or keep her family close by as she ages.

However, her closest neighbors, Patrick Devlin and Lynne Ballard, expressed concern about Vincent’s plans. The cottage was originally planned to sit 30 feet from their property line on a hill overlooking their pool, and the couple also worried about potential drainage issues created by the structure.

Last month, the couple’s attorney argued that language in the ordinance would prohibit the board from granting Vincent the special permit because the ordinance requires a home’s existing septic system to be able to accommodate the dwelling unit, and Vincent would be required to install a separate septic system for her cottage. However, Director of Planning and Development Eric Twarog said the intent of that language is to make sure the board doesn’t approve a dwelling unit that could not be serviced by an existing septic system, and does not prohibit the installation of a new septic system or upgrades to an existing system.

Devlin’s and Ballard’s attorney also raised concerns about drainage from Vincent’s proposed cottage, which Twarog said will be addressed during the next step of the project.

“All of that has to be approved by the building inspector during the construction phase of the project,” he said.