Cambridge-based King Street Properties has broken ground on a 144,910-square-foot speculative lab and office building.

The developer, which specializes in life science projects, expects to complete the 828 Winter St. project in Waltham in mid-2018.

King Street Properties acquired the property in 2015. It includes a fully leased 185,000-square-foot lab building at 830 Winter St. as well as the development site. The spec project will create a 330,000-square-foot campus.

The 3-story spec building will contain 48,000-square-foot floor plates and base building systems suitable for a wide range of office and lab tenants, King Street Properties said in a statement.

The lab vacancy rate in the Waltham/Lexington market was just 0.7 percent at the end of the first quarter, according to research by Transwestern Consulting Group.

Transwestern Consulting Group’s Eric Smith and Jon Varholak are the leasing agents.

Holliday Fenoglio Fowler (HFF)’s Greg LaBine and Porter Terry secured financing for the borrower through Blackstone Mortgage Trust. Loan proceeds will be used to refinance 830 Winter St. and construct 828 Winter St.

The project team includes architect Perkins+Will and general contractor BW Kennedy & Co.

Low lab vacancies in Cambridge and the suburbs also have prompted Boston-based Davis Cos. to go spec on a pair of life science projects in Cambridge.

A 37,500-square-foot lab building in Fresh Pond Technology Park is nearing completion. Davis Cos. also broke ground in February on The ARC, a 223,000-square foot speculative renovation and expansion of 35 Cambridgepark Drive, which is scheduled for completion in mid-2018.