Penrhyn Old Hall, including forecourt wall, steps and mounting block

This is a gentry house, largely dating back to the 16th century, with later additions and alterations. The oldest part is the left-hand cross wing, identifiable by its gable made of exposed stone and a tall stone chimney with a shouldered chimney breast. The house is constructed of stone, mostly rendered, with slate roofs. While many of the mullion and transom windows with red sandstone surrounds date from around 1900, reflecting later renovations, elements of the original building remain.

The right return features a three-light mullion window above a three-light mullion and transom window. A projecting chimney with a diagonal stone stack is situated in the angle between the cross wing and the central block, with two large stone chimneys visible to the rear of the central block. The central block incorporates two three-light windows on its first floor, one set at the eaves, and a single trefoiled window (reused from the 15th century) between them. A heraldic shield in low relief is also present. The ground floor is partially obscured by a modern porch, the openings behind which date back to around 1910. To the right, a cross wing is distinguished by its crow-step gable. It has a small attic window with two lights; two two-light mullion and transom windows to the first floor; and a single three-light mullion and transom window on the ground floor. A long, single-storey range, and a cross range with a crow-step gable, were added in the latter 20th century to southwest of the main building.

Slate steps lead up to the forecourt of the house. These steps are flanked by rubble walls, including a mounting block. The wall to the left sweeps down in a series of curves.

The southwest block contains a large ground-floor room, featuring a fireplace with a cambered beam decorated with leaf motifs and two male heads (resting on a modern shelf and pilasters). The room has a three-bay beamed ceiling, with longitudinal beams in the end bays, and some stop-chamfered joists are exposed in these bays. A wooden stair with splat balusters and twisted newels is also present. The upper floor of this block has an open roof with two collar-beam trusses. A partition at the northwest end displays wall-paintings; the apex features floral designs, and below this, to the right, a male figure appears in a roundel with the inscription "The Worde of God is Life to the Soul." A similar painting is fragmentary on the left side. Two fireplaces are located in the northeast and southeast walls of this block.

In the left section of the ground floor of the central block is a large fireplace with an oven and an original outside doorway. Stop-chamfered joists are exposed. The right section of the central block has steps leading up to the northeast wing, as well as an 18th-century cupboard, originally from the northeast wing.