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Life science developer King Street Properties added a Cambridgeport boutique lab building to its portfolio with a $9.5 million acquisition.

The 357-365 Allston St. property includes a 5,110-square-foot building originally constructed in 1950, according to Cambridge assessing data.

The purchase price works out to over $18,590 per square foot. Salem Five Cents Savings Bank provided $6.4 million in acquisition financing, according to a Middlesex County mortgage.

The seller, Biotech Realty Investors LLC, lists Hassanaly Ladha as manager, according to corporate filings. The previous purchase price in 2016 was $5 million.

The former vivarium was converted into office and lab space in 2022 in a projet designed by Boston-based Balance Architects. The current tenant, Biotech researcher Vaxess, has received more than $90 million in venture capital funding.

Boston-based King Street Properties did not respond to a request for comment.

The nearly 18 million-square-foot Cambridge lab market’s vacancy rate hit 21.6 percent at the end of 2024, according to a report issued this week by brokerage Colliers.

Nearly half of the lab inventory outside of East Cambridge now is available, including large blocks in Alewife at projects such as The Davis Cos.’ 101 Smith Place and developer IQHQ’s Alewife Park.