The Dormitory, built above an undercroft, was part of the eastern claustral range that was built between c. 1150-75. After a major fire in the early 13th century a programme of rebuilding was undertaken and a new dormitory was built and in use by c. 1225.

The undercroft was a substantial structure some 15.60m long N-S by 7.50m wide E-W, consisting of 4 bays formed by a line of 3 Upper Greensand columns, matching engaged bases set within the opposing walls. The columns would have supported low vaulting for an upper floor, which was the Canon's Dormitory, which must have therefore been of similar length and width. The dormitory was ideally placed, close to the Chapter House, with access to the Cloister, and perhaps also into the NE Transept of the church via a stairway at the southern end.

Access into the undercroft was via 3 doorways, to the north, east and west. The northern doorway was of double width and it is believed that the cool dark undercroft was used for storing wine, beer and other items. During the 15th century the undercroft was subdivided int two similar sized chambers, that to the north with access to the kitchen/cellarer's range probably still used for storage; whilst that to the south appears to have been a warming chamber for the canon's.

In the later 15th century the undercroft was reverted back into one large chamber. All was demolished at the Dissolution c. 1538.

Hicks, M., 1989, 'St. Gregory's Priory: The Church and Conventual Buildings' (Article in serial). SKE30366.

Hicks, A. & Hicks, M., 2001, St. Gregory's Priory, Northgate, Canterbury, Excavations 1988-1991 (Monograph). SKE30367.