Circa 1790. Classical mansion, 5 bays, 3 storeys plus sunk basement. Symmetrical set-back pavilions, 2-storey and central kitchen block to rear. Porch added circa 1820, single storey W wing added circa 1830. Sandstone ashlar to main elevations.
MAIN HOUSE: 3 storeys, symmetrical, 5 bays to S (front) elevation, central bay advanced and pedimented. Base course of light-brown sandstone in rock-faced ashlar, ground floor of rusticated ashlar with flat-arched windows. Cill course at 1st floor level, 1st and 2nd floor in broached ashlar, rusticated quoins, architraved windows. 2nd floor foreshortened, cornice and eaves course to pediment.
Central porch with 2 pairs of Doric columns, backed by simple squared pilasters, plain flat-roofed entablature with frieze, cornice and blocking course. 5 stone steps to platt. Front door 2 leaf, in
6 flush panels, decorative fanlight. flanked symmetrically by narrow windows to hall, panelled and glazed inner door.
Side elevations with 2 bays, stonework as front. E elevation has small windows added at 1st and 2nd floor, sunk basement evident. W elevation has 1 window infilled at 1st floor. Rear elevation 5 bays, squared and coursed rubble with ashlar quoins and raised margins. Basement, foreshortened 2nd floor. Central bay with leaded stairwell windows, dummy window to 1st floor. Door to basement.
EAST WING: 2-storey, upper floor foreshortened. 3-sided symmetrical front elevation in broached grey sandstone ashlar, raised cills. Other elevations harled, 3 bays to sides and rear. W elevation with piended lean-to with door at ground, blind window to 1st. Rear elevation with 2 blind doorways to ground, central doorway converted to windows, 1 blind window to 1st floor.
WEST WING: similar to E wing, with later extension adjoining to front. At upper floor, 1 dummy window to front, 2 to rear, 1 to E. 3 symmetrical windows to rear elevation, piended lean-to with door to E and to 2 storey link with main house, 1 blind doorway. Single storey extension to front in smooth ashlar with base course, cill course, cornice and blocking course, 3 bays to front (S), bipartite low window to W, all windows with architrave.
CENTRAL REAR BLOCK: 2-storey, upper floor foreshortened. Gabled to N with simple pediment, piended to main house. Harled, ashlar margins. To W elevation, 2 windows to ground. 1 tripartite, 3 windows to 1st floor. N (gable) elevation with 2 windows, 1 dummy, to 1st floor only. E elevation with 3 windows to 1st floor, 1 dummy, plus small glazed oculus, lean-to against ground floor, with door.
Windows timber sash and case, 12-pane to main elevations, except 6-pane in foreshortened upper floors. W wing of 1830 has lying panes to S elevations, multi-paned to bow window.
Roofs piended, grey graded Scotch slates. 2 large ashlar stacks to main house each with cope and 8 plain cans, small stack to front pediment with single can. Other stacks ashlar, coped, with plain cans.
ICE HOUSE: to rear of Alderston House, semi-circular front (S) elevation with ashlar cope, single central door. Vaulted, grassed over.