The barn at Henllys is an early 18th century, traditional, stone-built, slate-roofed structure of 7-bays, with 2 threshing-bays and is built down the sloping ground. The building is little used at present and has planning permission for conversion to holiday accommodation, like the other farm buildings, some of which are already converted.

Its walls are constructed of river stone with squared quoins to corners and boulder footings to gable-ends. Its gable-end walls have pairs of 3/4-tier ventilation slits with internal timber lintels.
The oak roof timbers consist of 6 collar trusses with notch lap-joints and a lapped apex, all pegged. At each doorway, there is one roof-truss, which has a tie-beam. The trusses support 3 pairs of side-purlins held by cleft pegs and a diagonally set ridge. The roof-truss timbers are roughly chamfered and have chisel assembly marks at collar. The rafters are flat section and notched to wall-plate with chamfered curved ends.
The full-height doorways with timber lintels have frames which are mortised, chamfered and pegged. One doorway has an extant double door in-situ, although possibly secondary, built in softwood.
A former floor (joists slots in wall) has been inserted between the upper gable-end and the first threshing doorway with surviving ceiling-beam. When this floor was inserted, some of the ventilation slits in the gable-end were blocked. This upper end-bay may have always had cattle as there are no ventilation slits at this level, compared to the lower end-bay. It must have been a natural progression to provide storage in the wasted space above the cattle, either for hay, or possibly grain.
The original form of the interior's ground-floor is obscured by later deposits.
At the north-west corner, a later cart-house/stable range has been added (NPRN407882).

The building was notified to us by Alice Pyper of Dyfed Archaeological Trust, through the Tir Gofal scheme and recorded by Geoff Ward & Nicola Roberts, 04/06/2008.