Gamble Garden's plan to replace its cramped greenhouse and build a new horticulture complex cleared its biggest regulatory hurdle Thursday when Palo Alto's Historic Resources Board voted to recommend approval of the project with modifications.

The board's recommendation now goes to Planning and Development Director Jonathan Lait, who will make the final determination on the renovation at 1431 Waverley St. in Old Palo Alto. The project is estimated at roughly $8 million, with construction targeted to begin in 2027 and completion expected in 2028.

The project will demolish the existing greenhouse, which executive director Mica Pirie has described as about the size of a one-car garage with dangling electrical wires and no climate control. A new greenhouse will be relocated closer to the Embarcadero Road parking lot for better solar access. A new horticulture complex will replace the existing potting shed, lath house and storage building, adding office space, a community meeting room and workshop space.

"It's just really not built for how we're using it today as a community resource," Pirie told Palo Alto Online on Aug. 12. "A major part of the project is updating a lot of that infrastructure, the electrical and climate control."

All three historic buildings on the property, including the 1902 Colonial Revival-style Gamble house, the carriage house and the tea house, will remain untouched. The work stays within the "working garden" area north of the formal gardens.

Gamble Garden is classified as a Category 2 Historic Resource, meaning any changes face extra scrutiny. A city staff report found the project complies with all 10 Standards for Rehabilitation, concluding the new structures respect the property's historic context while reading as contemporary additions.

Architect Jillian Kajori of CAW Architects presented the plans to the board. At least one board member suggested splitting the horticulture complex into two separate structures, but Kajori explained that would push construction further into the garden. The nonprofit was "adamant that once a building is constructed in a location like there will never be garden there again," she said during the Aug. 13 meeting.

The new complex will feature hipped roofs matching the historic buildings on site, with about two-thirds clad in wood and the workshop portion in metal panel. Its height stays below the carriage house peak. The building will also be "solar ready" under city green building code, with conduit and panel space for future solar installation.

Post-pandemic, Gamble Garden has seen a surge in visitors and volunteers but lacked the infrastructure to keep up. Weekly master gardener visits were scaled back to sporadic appearances because there was nowhere to host them. The nonprofit has been expanding classes and volunteer hours.

The property was originally the home of Elizabeth and Edwin Percy Gamble. Edwin was a son of the founding Procter & Gamble family. Elizabeth transferred the estate to the city upon her death in 1981, and the nonprofit Elizabeth F. Gamble Garden has managed it since 1985. The garden is open free to the public daily.

Lait's decision is the next step. No timeline for his review has been announced.