Tŷ Mawr is a Grade I-listed timber framed house in the township of Trefnant in the historic parish of Castle Caereinion, Montgomeryshire, Wales.

Originally occupied by the Lloyd family, descendants of Alo ap Rhiwallon who had settled in Trefnant in the 13th century, the house was re-discovered in 1971 and fully restored to its late 17th-century appearance in 1997–8.

[2] Tŷ Mawr was discovered by Peter Smith and Cecil Vaughan Owen in 1971, by when it was used as a farm building, clad in corrugated sheeting.

[7] The limewashed box-framed house, four bays long, sits on a stone platform built into the hillside, under a broad half-hipped roof (now replaced with tiles rather than slates, for which evidence was found in the archaeological excavations thatch).

[8] The two trusses within the hall are a single pair of chamfered wooden speres or posts set in the floor and forming a box-frame which carries the roof, and a pair of arch-braced base-crucks with two tiers of cusped struts above the tie-beam, which spanned the whole width of 7.5 m. The analogies are with the partly aisled halls of important houses in north-east Wales and north-west England.