Thornfield House, 9, 10, 11 Thornfield Avenue, Selkirk

Thornfield House, comprising three linked sections at 9, 10, and 11 Thornfield Avenue, Selkirk, dates to circa 1870 with later additions and alterations. The building is a 2-storey Italianate composition of 5 bays to the main house, a single-bay linking section, and a 5-bay annexe, all constructed in bull-faced sandstone with polished ashlar dressings. A base course and band course between ground and first floors run across the principal elevations.

The south-east elevation shows the grouped composition most clearly, with 1-5-1-5 bays across house, link, and annexe. The main house features a 5-bay frontage with an advanced tower to the outer left. A slightly advanced 2-bay gabled group to the centre has an advanced quadripartite window spanning both bays, with a window at first-floor level above each bay. A door with fanlight sits at ground level in the outer right bay. Two small windows at ground level occupy the bay left of centre, with a bipartite stairwindow above at first floor. The outer left bay contains a single-storey addition with a square plaque, eaves course, and shaped parapet. The linking bay is set back and contains a door with fanlight and a flanking window to the right. The annexe has a blank central bay, with windows to each floor in the immediately flanking bays; the first-floor windows break the eaves line with gabled heads. A door in the outer right bay has a plate glass rectangular fanlight above, with a first-floor window breaking the eaves line and gabled. The outer left bay has a small ground-floor window with a small first-floor window to the right.

The tower rises in three stages, slightly advanced from the main wall. A band course divides the second and third stages; a cill course runs at the third stage with a moulded string course at the shoulder. On the south-east elevation, a panelled door at ground level has a semicircular fanlight above and a pilastered, consoled, and corniced doorpiece. A window occupies the second stage, with two round-arched windows at the third stage and a round opening to the gablehead. The south-west elevation of the tower has a single-storey addition at ground with an asymmetrical bipartite window, a window at the second stage, and round-arched lights to a tripartite window.

The south-west elevation shows an enlarged central opening at ground level with modern plate glass sliding doors and fanlight, with a first-floor window above. A slightly advanced bay to the left has a former bipartite window at ground level, recently altered to a door opening with a window to the right, and a bipartite window at first floor above.

The north-west elevation is an 8-bay frontage grouped as 2-1-3-3 bays. The central 3-bay group has a cill course at first-floor level, with windows to each bay at ground and windows flanking the centre bay at first floor, breaking the eaves with gabled dormerheads. A 2-storey, 3-bay advanced group to the right has a band course between floors and corbelled cills to each window. Bipartite windows occupy the centre bay at each floor, with canted 3-light full-height windows to each flanking bay, having bipartite windows to the centre light of each. These sweep to square at the gablehead, each with a roundel in the left bay, gabled. A single-storey, single bay to the left of the central group is gabled and blank, with a bipartite window breaking the eaves and a gabled dormerhead; the north-east return elevation has a further small window to the left. The outer left 2-bay group has a recently blinded window at ground level in the left bay with a first-floor window above breaking the eaves as described, while the right bay has a modern flush door with a plate glass rectangular fanlight at ground level and a first-floor window as above.

Windows throughout are 4-pane and plate glass timber sash and case types. Slate roofs cover each section. Ashlar coped chimney stacks rise from the main house, some with stencilled cans. A wallhead sandstone and coped stack marks the centre of the south-east elevation of the annexe, with a further wallhead coped stack to the gablehead of the left bay of the central group on the north-west elevation.

Interior features include timber panelling dado to the hall and stair, with a timber stair banister.