The day room at Fountains is part of the E range, being continuous with the offices on the E side of the cloister; it is aligned N-S and above it was the S end of the monks' dormitory. The monks' day-room used to be called the sub-dorter or dormitory undercroft.

The day room is reached through a doorway at the S end of the E cloister walk, there was a passage formed in the N bay which led E to the monks' infirmary. That left a room 2 bays wide and 6 bays N-S. Of this, only the lower parts of the central arcade remain.

For further information, see report for Fountains Abbey, church.

The day room 'was vaulted in seven double bays from a central row of piers. The northern bay was partitioned off to provide a through passage from the cloister to the infirmary' (Coppack 1993, 45-6). Two reused capitals are now seen inverted as bases to the mostly northerly two piers; it is thought these may have come from Abbot Murdac's chapter house (Coppack 1993, 46).

Gilyard-Beer says 'this undercroft is a later twelfth-century remodelling of an early twelfth-century building, much of which remains incorporated in its walls' (1970, 48).

In the thick W wall, adjacent to the fireplaces of the warming room, is a side chamber formed of three small cells.

The ribs of the vault appear to have been chamfered, to judge by the remnants on the N respond. The room had groin vaulting, according to Coppack 1993, 45.