Early 17th century cross-passage house. The present house was built in two main stages with the hall, cross-passage and centre service rooms dating from c1600. A straight joint in the external masonry shows that the parlour block was added later, probably c1610. This interuption in construction is puzzling because, although built later, the parlour is an integral part of the original design. Fox and Raglan's explanation is that a medieval hall-house may have existed on the site, and c.1600 the first part of the new house was built next to it. Shortly afterwards the old hall was demolished to make way for the new parlour block, which completed the original design. Transom windows and new doors were added in c1690, and it was probably at this time that the fireplace stair in the parlour was blocked and a new stair built against the partition in the centre lobby. An additional kitchen wing was added to the rear, probably in the late 17th century. Since then there have been relatively few changes and the house survives largely unaltered. In the early 18th century Upper Tresenny belonged to the Parry family, and later (through marriage) the Hughes.

A substantial, two storey and attic farmhouse constructed of whitewashed rubble stone with brick end-stacks and slate roof.The flat-headed entrance doorway to the cross-passage is off-centre with a plank door with strap hinges. The hall (to left) has a late C17 transom window on ground floor. To the right of the cross passage, there is a blocked doorway with an inserted window which has a central mullion, while to the parlour is an C18 12-pane iron-framed window. The first floor has a tiny, stone, round-arched light to the fireplace stair, a 4-light, sunk-chamfered mullion window, an upper loading door with two fielded panels, a former 4-light diamond mullion in a chamfered frame, a C20 casement with C17 angled dripstone, and a tall two-light mullion, now blocked.

The north gable has 2-light window to the fireplace stair and C17, two-light mullion windows on the ground and first floors, the upper one with a bar dripstone supported on shaped br ackets. The rear elevation has more surviving features from the original house, including a 3-light mullion window in a false mitred frame on the upper floor and the cross-passage entry. The original passage entry, which had monolithic jambs, has been reduced in width and has a segmentally arched head with voussoirs and a keystone. The door is C18 with beaded boards and strap hinges. To the left of the cross-passage is a C20 window, and late C18 9-pane metal casement, with a similar window above.

The internal plan is three unit with a cross-passage plan. The hall is to the left of the cross passage, and the service rooms and parlour are to the right. The cross passage ceiling joists are chamered with diagonal stops, and on each side of the cross-passage are fine, early C17, post and panel partitions with four-centred arched doorways. The doorway to the left is blocked and retains the original c1600 door, while the three other doorways have C20 boarded doors.

The two small service rooms are separated from the adjoining parlour by a third transverse post and panel partition. The parlour has deeply chamfered beams, also with diagonal stops. To the left of the fireplace is an opening with a finely-worked, stone, keel moulding to the right jamb which is probably reused from elsewhere. The attic, which is directly above, has similar keel moulding, suggesting a fireplace stair formerly existed in this position. The attic has collar and tie beam trusses and two rows of purlins.
(Source; Cadw listing database) S Fielding RCAHMW 18/01/2007