Pant-glas Farmhouse and its associated barn at Llanishen, Trellech, Monmouthshire date from the early 16th and 17th centuries respectively and are both Grade II* listed buildings.

[3] Although of a construction date of 1590 to 1620, the house uses much material of earlier dates, including medieval stonework and an Elizabethan doorcase and the architectural historian John Newman notes the suggestion that some of the masonry came from Raglan Castle, 4 mi (6.4 km) to the west of Pant-glas.

[1] The complex building history leads Newman to call the house a "fascinating puzzle"[1] and Cadw notes its construction is open to "several possible interpretations".

The entrance front was re-designed in the 18th century, to give what Cadw describes as a Georgian appearance.

The roof has a steep pitch and is of concrete and Welsh slate tiles, with dormer windows dating from the 1970s.