20 Mill Square, 18, Catrine

16 Mill Square in Catrine is an early 19th-century building consisting of a two-storey and attic row of seven flatted dwellings, which ends at a corner. The exterior is dry-dashed with painted ashlar dressings, featuring quoin strips, a base course, and an eaves course. The first-floor windows are positioned just under the eaves. There are four doors (one of which is glazed and functions as a window), one small and three large windows, along with a three-bay former shopfront at ground level; the first floor has seven windows. The roof features three piend-roofed dormers, with one canted to the left and a pair of bipartites to the right.

The building has a two-bay return elevation facing Bridge Street, which includes a larger window on the ground level to the right, a wallhead stack, and a canted piend-roofed door. The rear elevation is plain, with brick forestairs located at the center.

The windows are timber sash and case, with 12 panes each. The roof at the corner is piended, covered with grey slates, and has ashlar coped skews and brick stacks.