Valve House on former filter beds on Afon Sawdde below Llyn y Fan Fach Reservoir, including weirs

The Valve House is located on a high battered base made of rock-faced stone, with the rest of the structure built from quarried stone featuring rock-faced quoins. It has a hipped slate roof with swept eaves that contribute to its distinctive appearance. The main entrance is a doorway in the east wall, which is topped by a concrete lintel. The north wall has a single-light window, while the west wall features a mullioned two-light window with concrete dressings. On the north side, there is a later outshut with a corrugated asbestos-cement roof. This outshut includes a doorway at basement level on the west side facing the dam, which is located below a two-light wood-framed window, both under concrete lintels. Additionally, there is a boarded-up doorway in the north wall, along with further stone and blockwork additions on the north and east sides of the outshut.