Image courtesy of EMBARC Studios

After sitting vacant for decades amid failed redevelopment attempts, the Alexandra Hotel in Boston’s South End is due for a makeover and expansion.

Boston Planning and Development Agency directors Thursday approved JB Ventures and TCR Development’s proposal to build a 150-room boutique hotel on the site and an adjacent vacant lot. Designs by CBT Architects call for a 12-story, 66,000-square-foot structure at 631 Massachusetts Ave. and 1767 Washington St. including a 12th-floor restaurant and roof deck.

The facade of the original 1875 hotel will be retained, but the rest of the building will be demolished because of structural problems, according to BPDA filings.

Also at Thursday’s meeting, BPDA directors approved a large commercial expansion to Charlestown’s Hood Park.

Owner Catamount Management Corp. of Lynnfield is seeking to tap into the rising demand for class A office and lab space along the MBTA Orange Line north corridor. The updated master plan for the 20-acre site includes a 232-foot-tall office tower at 10 Stack St. with 350,300 square feet of office and lab space. Indigo Ag Inc., an existing tenant of the park, is seeking room for expansion, according to the developers. A 150,000-square-foot addition to the 100 Hood Park Drive office and lab building also is under construction.

BPDA directors also approved large multifamily housing developments in Brighton and West Roxbury.

AvalonBay Communities plans a 228-unit multifamily complex at 139-149 Washington St. in Brighton, comprising two new residential buildings containing 180 and 48 units, and 228 parking spaces.

In West Roxbury, Lincoln Property Co. gained approval for a a 254-unit apartment complex in two four-story buildings at 1545-1555 VFW Parkway, with 387 garaged parking spaces. The project is estimated at $70.1 million.