Llanthewy Road Baptist Church and attached Sunday School wing

This is a large Baptist chapel constructed in an Anglican style, dating from the 18th century. The building is of snecked coursed rubble with pale ashlar dressings and a Welsh slate roof. The plan incorporates a nave, transept-like bays, a porch bay with an adjacent tower, and an attached Sunday School and hall wing.

The asymmetrical front facade is dominated by a large window of six lights with quatrefoil tracery, a hoodmould, and foliage stops, with a single cusped light to its left. Below this is a projecting porch bay with a steeply gabled roof, a heavily moulded entrance doorway with paired colonnettes and an overlight with cusped tracery. The quoins of the doorway are tapered to the kneelers, with cusped lights on either side, low buttresses, and a second door to the left. To the right and projecting forward is a slender tower, featuring full-height angle buttresses with shallow offsets and a crenellated parapet incorporating a cross. A string course below the parapet marks the ringing chamber, which has tripartite louvred openings, heavily moulded with hoodmould and slender columns. The tower chamber has lightly cusped lancets, while a blind arcade frieze runs across three sides of the tower. The tower doorway at ground level is similar to the main entrance, and dedication stones are located at the base of the buttresses.

The side elevation, accommodating a steep slope, is characterised by a lower ground floor. The steeply pitched roof has three ventilators, and a four-window range of paired cusped lights with quatrefoil tracery, separated by long, slender buttresses without offsets. A gabled cross wing has a similar window to the gable end, a trefoil light, and cross-framed windows to the lower ground floor. An additional lower entrance bay is attached to the right. On the opposite side, the cross wing connects to the Sunday School, which features similar cusped-headed lights, paired and triple, and a central gabled porch with overhanging eaves and moulded pointed arched doorways to either side. Paired lights to the side are separated by tall, chunky buttresses with swept offsets. Lower-level rectangular windows to the right are blocked.

Inside, the chapel is airy and features a wide pointed chancel-type arch supported by corbels with clustered half-colonnettes. There is no gallery. The roof is of a boarded, wide-span hammer-beam style with ventilators, supported by heavy corbels. The interior is dominated by a semicircular, apse-shaped baptistry with a stepped red terrazzo floor incorporating an unusual raised grey terrazzo baptismal pool for total immersion. There are cusped lights on either side of the arch, and a large three-light window with quatrefoil tracery to the baptistry. Matching side windows of two lights with quatrefoil tracery contain some figurative glass by Pearce and Cutler of Birmingham, while other windows have tinted glass with decorative tracery leading. The interior is fully pewed with a boarded dado, with an organ on the left and a pulpit on the right. Half-glazed doors lead to outer rooms and passages. The vestibule has a boarded dado, half-glazed swing doors with boxed entrances to the sides, and a central doorway flanked by paired cusped-headed lights.