Peter Smith describes its original form as ‘a commoner type of hall where there is only one aisle truss sited as a screen between hall and passage….. The construction is mixed, box-framed aisle truss and cruck-framed central truss, the disparate elements linked by the general use of a king-post to carry the ridge.’ It would have been was a very grand house indeed; it was more ornate than most hall houses of the period and the craftsmanship was of the highest standard - very much a house of the aristocracy.
However, the form it presents today presents a radical reconstruction which took place in the 16th century, when the first floor was inserted with heavy moulded beams. The walls are now of stone rubble and the north and south entrances have four-centred arches and jambs typical of the 16th century. No trace of the west wing survives and the east part of the house was altered again in the 17th century.
In the late 16th century the barons of Cymmer moved to Gwerclas, a house nearby, and took the name of Hughes of Gwerclas; but Plas Uchaf remained in their possession and in 1707 it was listed by Edward Llwyd as being one of the houses of the gentry of Llangar. After that it embarked upon a steady decline that continued until 1972. By 1825, when the Gwerclas estate was sold, it seems to have been the farmhouse attached to the home farm.
It then became part of the Rûg estate belonging to Griffith Howel Vaughan. Between 1826 and 1885 it was first lived in by labourers and then by a tailor and his family. There is a tradition, locally, that at about this time the first floor room above the hall (that has now gone) was used as a religious meeting house. In 1913, it was described as a tenement, and in 1933, it was a gamekeeper’s house. The last people to live in Plas Uchaf were the Owens, who were there in 1960 and who now farm a few miles to the south.
In the early 1960’s Lord Newborough, the head of the family that had acquired Plas Uchaf in the early 19th century, sold the (then unlisted) house to Mr Lloyd Jones of Bala. The new owner sold the 16th century beams and panelling to America: in a way this was a pity, but it did also return Plas Uchaf to its original form: that of a medieval hall house, open to the roof. More unfortunately, having been virtually gutted, Plas Uchaf was left derelict for ten years.