Barn at W side of farmyard at Y Dderw

The barn at the west side of the farmyard at Y Dderw was built in 1681 and rebuilt in 1854, as noted on a panel above the south porch door. It is constructed of rubble stone and has a concrete tile roof. The barn features ten bays, with two-bay porches on the east side of the third and eighth bays, and a contemporary lean-to cowhouse located between and against the end bays. There is a central cross bay on the west side over bays five and six.

The walls include slit vents, and the south gable has three square vents framed in timber with diamond mullions, under a chamfered external lintel and stone drip courses with dropped ends. The gable also contains nine tiers of pigeon nest holes with flight ledges, totaling approximately 54 nests, as well as five tiers of nest holes on ledges above the segmental ashlar arches of both porches.

The original structure likely included some timber framing between the gable ends, with the main posts integrated into the stonework in the 19th century.

Inside, both end bays appear to have been floored, with the south bay retaining a floor and timber sill against the winnowing floor. The tops of the 17th-century jowled timber posts are still visible, featuring angle struts to the ties. The barn has tie beam and principal rafter trusses with pegged canted struts. The cowhouse at the angle with the south porch has a ventilation slit opening into the midstrey-porch.

This barn is noted for its interesting evolution from a 17th-century corn barn into a well-built and well-preserved mid-19th-century farm building.