11, Marlborough Street

11 Marlborough Street is a terrace house built around 1790 to 1793, with 19th-century alterations, designed by John Palmer. The building features a front and rear made of limestone ashlar and has a Welsh slate double pile parapeted mansard roof, which is currently coated with sealant. The roof includes a coped party wall with a single large ashlar chimney stack shared with No. 12 Marlborough Street, which has some early clay pots.

The house is three storeys high, with an attic and basement, and has a single-bay front with three windows. The first floor showcases a Venetian window with plate glass horned sashes set in splayed reveals and a continuous stone sill. The second floor has three grouped plate glass horned sashes, which are narrower on the left and right, also in plain reveals with a continuous stone sill. On the ground floor, to the right, there is one plate glass horned sash in a splayed reveal with a stone sill, and to the left, a six-panel door featuring reeded, fielded, and glazed panels within a moulded stone doorcase that has a beaded reveal, panelled pilasters with console brackets above, and a moulded cornice. The opening to the basement below the ground floor window is now filled with glass blocks, and there is a double dormer with plate glass sashes. The building also has a timber bressumer, a stone band course over the ground floor, a frieze, a moulded eaves cornice, and a coped parapet. The rear elevation includes plate glass horned sashes, a sash with coloured glass borders at the first half landing, a small ashlar extension at the ground floor, and a lead hopperhead.

The interior has not been inspected. This property is part of an incomplete development of St James's Square, situated on land leased by Fielder, King, Hewlett, and Broom from Sir Peter Rivers Gay on March 25, 1790. Marlborough Street serves as one of the four diagonal approaches to St James's.