SU 5877 is likely part of an earlier tufo slab floor in the space of Room 20. The tufo is very degraded and in places breaking off - to the southwest it has clearly been cut for the insertion of ashlar block 5884. The slabs also have some cuts into them, with one likely having been a post hole. They seem to run further east under part of the floor that was not removed, and are in fact quite similar to slabs SU 5872 on the east side of the room.