Preliminary plans have been submitted for a five-story addition to an existing three-story office building at 2300 Harrison Street, the former headquarters of Lyft.

The idea, still in its early stages, is to build two levels of office space and two levels of housing on top of a mixed-use ground floor and basement-level parking spaces. The new building would go on what’s now a parking lot surrounding the existing office building.

Overall, the project would add some 26,600 square feet of office space, and nine units of market-rate housing. Though it would include 41 parking spots, that would actually be a net decrease from the 66 spots now available. The building will rise to about 65 feet in height, and would have a connection to the existing office building.

The project sponsor, represented by a real estate law firm, did not return a request for comment by publication time. A spokesperson for the Planning Department, Gina Simi, indicated the plans are still in the early stages. The plans submitted are part of a process that evaluates projects before any applications are filed.

“This is to allow the Department to provide sponsors with feedback and procedural instructions from the beginning in the development process,” Simi wrote.

The building became the ridesharing company’s headquarters in 2014, but Lyft moved to China Basin in 2016. It’s unclear what the office houses currently.