20 Cathcart Street, Ayr

20 Cathcart Street in Ayr is an earlier 19th-century house that features two storeys, a basement, and an attic, arranged in a three-bay rectangular plan on a corner site. The exterior is finished in painted ashlar and includes ground and first-floor band courses, an eaves course, a cornice, and a blocking course, with painted margins around the window openings.

The northeast elevation, which serves as the entrance, has a central stepped platform that oversails the basement. It features an Ionic-columned doorpiece with a modillion cornice, a central panel in the block pediment, a timber door, and a patterned letterbox fanlight. Above the entrance, there is a single window aligned at the first floor, with flanking single windows at both the ground and first floors. The basement to the right is infilled, while there is a timber glazed door to the left and a modern window to the right. The attic has segmental-headed single dormers on both the outer right and left sides.

The northwest elevation, facing Fort Street, shows regular window arrangements at the ground and first floors, with infilled windows in the centre and left at the first floor. This elevation also features a pedimented gable and has a boundary wall adjoining to the outer right.

The house has 12-pane timber sash and case windows at the ground and first floors, with a modern window at the basement on the left. The roof is covered in grey slate, with corniced gablehead stacks and circular cans.

The interior was not seen in 1998. The boundary wall and railings consist of a partly coped rendered brick wall along the northwest elevation. Ashlar copes topped with iron railings featuring spike finials flank the entrance steps and enclose the basement frontage on Cathcart Street.