Hirlwyn Isaf and outbuilding

Hirlwyn Isaf is a farmhouse with an attached agricultural range, forming an L-plan group. The farmhouse is constructed of colourwashed rubble stone with a slate roof and end-wall stacks, featuring rubble stone on the left and brick on the right. It is two stories tall with a long three-window range, which is notably offset to the right. The small casement windows are located under the eaves, with the left window replaced by a single pane. On the ground floor, there are 4-pane sash windows on each side of a plank door, which originally had timber lintels but has since been replaced with concrete fence posts. The stone sills are present, and the door is misaligned with the window above, being set to the right. The end wall is made of rubble stone, and there is no outshut at the rear.

To the left of the farmhouse is an outbuilding that serves as the end wall of a long barn and stable range extending back. This structure has a slate roof that is hipped at an angle and is made of whitewashed stone. There is a door to the left of the house with stone voussoirs between vent loops. The long return facade is hipped to the right and gabled to the left, but it was likely originally shorter and also hipped at the left end, which would have positioned the barn door closer to the center. This barn door is partially blocked, and there is a square loft window and a vent loop further to the right, with the stable located to the left. The stable features a door situated between two windows, both with timber lintels. The barn and stable doors have stone voussoirs with cambered heads. Another loft light is located to the left of the stable, and the upper end has a single door with stone voussoirs. The roof of this end partially collapsed in 1998, and the upper corner adjoins an added barn that is listed separately.