Gelli-siriol farmhouse

Gelli-siriol farmhouse is a building constructed from Pennant sandstone, partially coursed, and set on boulder footings, with a slate roof that has replaced the original stone tiles. It was originally designed as a single storey with an attic but has been modified to two storeys. The main elevation faces south and features a front entrance with a round arched opening that is enclosed in a gabled porch.

The windows are plain chamfered mullioned types made of precast stone with label hoods, which have replaced the original ovolo-moulded stone windows. There is a three-light window on the south elevation of the hall and a two-light window above it in the chamber. A similar plain-chamfered window was added in the gable of a 1990s extension at the east end. A stone relieving arch is positioned above the hall window. Other windows include timber casement types, with two new windows on the north side, and a small slit window that lights the external stair extension. The building features stone stacks.

According to a survey by the Royal Commission on the Ancient and Historical Monuments of Wales in 1972, the central living hall contains round-headed doorways on either side of the central stack, a timber fire lintel above the principal fireplace, and reed-moulded ceiling joists with ornate curved-fillet stops. The floor is flagged. The roof structure includes a tie beam and principal rafters with a notch-lapped jointed collar that supports three tiers of trenched purlins. The east room has a voussoired round arched doorway leading to the stair in the corner.