1. House all of one build. Plain elevation.

2. Nantst-ystalwyn House is situated along a track which runs north off the minor road between Tregaron and Beulah, in the middle of the Tywi Forest, and lying parallel with the Afon Tywi to the west (unusual for this district). It is a large early 19th century farmhouse in an upland setting, reflecting a change from mixed farming to specialist sheep rearing. It is a long 2-storey range with the house to the right end and service unit to the left. There is a small adjoining bakehouse at right angles to far left of the building. The building is constructed of rubble stone under a slate roof with a projecting stone stack to right end and brick ridge stack to the centre with a small skylight in to the roof pitch. The house at the right end is 3-window, the central openings offset slightly to the right. The entrance contains a half-glazed planked door, the light boarded over. The flanking windows are also boarded, although that to the right is partly visible as a sash. The openings all have flat heads and stone sills. Those to the upper storey are 3-over-3-pane horned sashes and that to the left, boarded over, and aligned with the openings below. To the left of the brick stack is the joint of a former doorway, left of which is a late 20th century window. Further left, in the angle with the bakehouse, is a planked door under a shallow segmental head of stone voussoirs. Above is a 3-over-3-pane horned sash under a similar head. The single-storey bakehouse has a stone ridge stack offset to the left and planked door offset to the right, rising to the eaves, and signs of alterations towards the centre of the wall. There is an opening to the gable end offset to the left. The rear of the house is cut into the hillside, but has a 4-pane window to the upper storey towards the centre of the house part, which must light the stairs. Opposite the house stand the outbuildings, mostly in parallel ranges, with the house. The house had a central stair-hall arrangement with hall to left and parlour to the right. The long adjoining service unit or 'back-kitchen' to the left is contemporary and there is no division from the rest of the building. It was listed as a rare and unaltered example of an upland farmhouse built for a specialist sheep farmer, which marks an important change from the long-house tradition.
(Source: CADW listed buildings database; Brycheiniog 1963, Jones and Smith, 'The Houses of Breconshire', p. 58).
Ian Archer, RCAHMW, 11th February 2005