Old Auchentroig

Old Auchentroig is a laird’s house dating to 1702, with a small later, late 19th-century addition and a restoration carried out by Simpson and Brown in 1999. The building is rectangular in plan, with a single-storey outbuilding attached to the northeast. It is two storeys and an attic in height, presenting a symmetrical, double-fronted principal elevation to the southeast, with crowstepped gables featuring beaked skewputts. The walls are of harled rubble with sandstone dressings, while the single-storey addition is constructed of coursed sandstone rubble. Flush-chamfered architraves frame the windows.

The southeast elevation, the principal facade, has a central entrance with a roll-and-hollow moulded architrave topped by a datestone inscribed '17 MS.IM.BG 02', bearing the initials of John McLachlan and likely his wife. A studded timber door, a 1999 replica of the original, stands within, and a heraldic panel above displays the McLachlan coat of arms, including a lion rampant and a salmon naiant, surmounted by a crest. Flanking windows are present on both the ground and first floors. A late 19th-century, single-storey outbuilding adjoins the right side of the elevation, with an entrance on its right side.

The northwest elevation includes a ground floor window to the right of center and a window to the right of the first floor. A later 19th-century, single-storey outbuilding is set back to the left. On the northeast elevation, a late 19th-century single-storey outbuilding projects to the left of the ground floor, with a window to the right and one above. A small attic window is located to the right of the gable end. The southwest elevation is a blank gable end. Walled gardens adjoin the building on either side.

The windows are 4-pane timber sash and case. The roof is grey slate, with a single-pitch corrugated iron roof covering the single-storey outbuilding. Coped gablehead stacks are present on the southwest and northeast sides, although the cans are missing.

The interior retains the original layout, with two rooms on each floor flanking a central staircase, a straight flight of wooden stairs. A large segmental-headed fireplace is located in the ground floor southwest room, the original kitchen, featuring an early wrought-iron fire grate. An original roll-and-hollow moulded fireplace surround is in the upstairs northeast room. The original front door, constructed of two layers of timber planks—vertical externally and horizontal internally—studded with wrought-iron nail-heads, and incorporating its original latch, lock-mounting, knocker, and crook-and-band hinges, has been retained as a feature within the kitchen. Six-panel timber internal doors, previously recorded by the Royal Commission on Ancient and Historical Monuments in 1952, are presumably intact. The building retains most of its original roof timbers, largely jointed and pegged and bearing carpenters' marks, and the majority of the original sarking boards.