After a lengthy public process that included a spirited debate among some Lans-downe residents, the Loudoun County Board of Supervisors voted unanimously Tuesday to buy land at the National Conference Center in Lansdowne as the site of a new high school.

The school, currently known as HS-8, will be built on a 46-acre site north of Route 7, off Belmont Ridge Road. The parcel, which will be subdivided from the center’s existing 112 acres, will be purchased by the county for $20 million, officials said.

County leaders have referred to the school as the final component of a “three-school solution” for Ashburn, intended to alleviate crowding that has become an increasing problem throughout the school system and especially in eastern Loudoun. School officials have long warned of a rising seat deficit as roughly 3,000 new students join the school system each year.

The selection of the National Conference Center site followed numerous community meetings, at which some Lansdowne residents expressed a preference for the Lexington Seven property, an alternative 76-acre site off Route 7, near the Loudoun County Parkway.

The school, which is expected to open for the 2015-16 school year, will be built as a co-located facility near Belmont Ridge Middle School, which is just south of the site on the National Conference Center property.

Some nearby residents have expressed concern about the two schools’ effects on traffic, saying that Lexington Seven is a more viable choice. But other residents of Lansdowne and Ashburn appeared at a public input session Monday dressed in green shirts, symbolizing their wish for the county to move forward with the project.

Several of the green-clad speakers acknowledged that the site had positive and negative aspects but said that the need for a new high school outweighed their concerns.

“It sits almost in my back yard,” Lansdowne resident Sharon Mundie said of the school’s location — a block from her home — “but to ensure our children a school, I am so happy to go with it.”

At the meeting Tuesday, board Vice Chairman Susan Klimek Buckley (D-Sugarland Run) said she thought the time had come to make a final decision on a long-debated issue.

“We don’t make this decision in a vacuum. We have talked about this for years; we have worked on this issue for years; we have looked at options and options and options,” she said, calling the site “the right school, at the right location, at the right time.”

She noted that the terms of purchase allow for a 120-day due diligence period, which will allow the county to examine any remaining concerns about the site before the purchase is final.

“Are there some issues to be addressed? Yes. Are there some questions to be answered? Yes,” Buckley said. “But that’s exactly what a due diligence period in a contract is for.”

Board members also emphasized the county’s intent to maintain community involvement during the planning and construction of the school.

Chairman Scott K. York (I-At Large) asked county staff members to continue to meet with community members throughout the process, “because not all are in agreement. They’re very concerned about the impact, and we understand that,” he said.

The public will have the opportunity to provide input at two public hearings next year, county officials said.

Supervisor Lori L. Waters (R-Broad Run), who proposed the motion, said it was important that the development of the school take priority and stay on schedule. She also applauded members of the Ashburn and Lansdowne communities who worked together on the project.

“It is not often when you have a group of people that come forward and say, come to our community and build something,” Waters said, prompting laughter on the dais.

She added that the same communities were “very divided” during the process of drawing boundary lines for Tuscarora High School.

“We’ve now come full circle, to where these communities are working together and recognizing a need, because they’re putting the kids first,” Water said. “And I think that the kids will appreciate that too, and see that together we can achieve much.”