Runcol Building R3 (Carillion Building 65) at Rhydymwyn Valley Site

The Runcol Building R3, also known as the Carillion Building 65, is a rectangular structure located at the Rhydymwyn Valley Site. It was constructed with a concrete frame and features infill panels made of red brickwork laid in English bond. The building has a flat roof and faces the roadway, consisting of six bays, with the first and fourth bays being broader than the others.

At the southeast end, there is a narrowed doorway and a window above it with small-pane glazing. The southwest elevation includes two low rectangular blocks that were originally used as a pump room and syrup room, with stairs situated between them. The northwest end has a window at the upper level that has been reduced in size.

Internally, the building is divided into two areas. The longer southeast area, known as the reaction section, has a raised platform on the southwest side that once supported production equipment. At the northwest end, there is a doorway leading to the acid generator section. An overhead crane and some internal details from the building's operational past remain visible.