Plas Glascwm is a substantial multi-period farmhouse of L-plan with the earlier house refronted in the early C19th. A lean-to dairy and service range with a composite water-wheel c2 metres diameter has infilled the remaining space between older and newer ranges. The later house presents a hipped main front of central entry type with elaborate porch, and has a lateral fireplace with ogee stops (of uncertain date) heating the best kitchen. The earlier house, now the back kitchen, was of Snowdonian type. The large projecting end fireplace (without stair but with oven projection) survives along with chamfered beams with curved stops. The bolted truss appears C19th but the earlier purlins and rafters have been reused. Dendrochronology showed that these dated from the later C16th. Noted in RCAHMW, Caernarvonshire Inventory, Volume I: East (1956), p.175, mon. 626. RFSuggett/RCAHMW/July 2012.

Summary of tree-ring dating:
Six timbers were sampled for dendrochronological analysis, two from the kitchen ceiling, and four from the roof. Two roof samples were dated, one being from a tree felled in winter 1570/71 and the other in spring 1573. This strongly suggests that construction of the property took place in 1573 or shortly after. The remaining four sample series matched each other, and were combined into a site master chronology, but this remains undated, although it may be contemporaneous with the dated material. Oxford Dendrochronological Laboratory Report 2012/27. RFSuggett/RCAHMW/July 2012.