Garage/coach house range at Plas Tregayan

The garage and coach house range at Plas Tregayan is a lofted linear structure built in 1839, facing northeast and forming the northeast side of an enclosed courtyard. It is constructed from rubble masonry, with the principal elevation featuring dressed, coursed stone. The building has a slate roof with a squat gable stack at the southeast end, which is raised by brick.

At the left end, there is a shallow basket-arched opening with chamfered jambs and a slightly stressed keystone. Above this arch, a stone tablet displays the name "ADMIRAL LL" along with the date "1839." To the right of the arch is a single doorway with a flat arch, and a modern casement window is set under the eaves between this doorway and the arch. There are also two loft windows along the range to the right. At the right end, four double garage doors are flanked by stone piers and are covered by a long rolled steel joist (RSJ) with an iron and glass canopy above. External stone stairs at the end of the range lead up to a loft doorway in the northwest gable.

A single-storey addition extends along the northwest end of the rear wall of the coach house, featuring a catslide roof. Another single-pitched outbuilding has been constructed at right angles to the northwest corner of the addition. Access to the addition is through a flat-arched doorway in the northwest gable, while another doorway opens into the courtyard at the rear of the range, flanked by small paned sash windows. The single-pitched roofed outbuilding now has a roof made of profiled material and includes a single doorway in the southwest gable, with the principal doorway in the southeast wall having flanking ventilator windows.

The interior of the coach house appears to have been modernised during alterations made in the early to mid-20th century.