90a, Harley Street W1

No. 90A Harley Street is a house built in 1912 by Sydney Tatchell, located facing Weymouth Street and adjacent to Tatchell's contemporary No. 90 Harley Street town house. The building is constructed of Portland stone, featuring a channelled ground floor and rusticated quoins. It showcases sharply profiled linear classical details similar to those of No. 90, but on a smaller, domestic scale. The house has two storeys and a dormered mansard above a basement, with a symmetrical front that is five windows wide.

The central porch, a smaller version of the one at No. 90, includes a deep-set, splayed semicircular arched doorway with an ornamental iron balustrade above the cornice. The windows are recessed glazing bar sashes, with those on the first floor set in eared architraves that have a pulvinated frieze and cornices rising into the main frieze, along with apron panels. A narrow first-floor plat band, fluted frieze, and cornice with a balustraded parapet are also present. The central dormer features a triangular pediment, flanked by segmental pedimented dormers. Additionally, an ashlar single-storey screen wall extends to the right, and ornamental cast iron area railings are included. This house exemplifies the early 20th-century effort by the Portland Estate to reintroduce a domestic character to an area that had become predominantly professional.