The water balance incline was built after 1861 and is visible on an 1885 plan held by J. W. Greaves and Sons Ltd. The 1st edition Ordnance Survey map shows the incline has been taken out of use, although the drumhouse was mapped. The only surviving element of the structure, and one of the earliest surviving features of the quarry, is the drumhouse.

This is of coursed slate construction and comprises a base 4.9m x 3.4m upon which 3 slate piers were constructed. The structure originally had a pitched slate roof, and there are the partial remains of an external stair on the north side. The rotational forces which would have been caused by the operation of the Incline are visible in the joint between the base and the slate piers. None of the machinery or the incline itself survives and the water supply method for the incline is not recorded on any of the contemporary maps or plans.

The incline ran down to the west of the drumhouse and was originally constructed to transport slate up from an adit entrance on Level 2. This formed part of the early tunnel quarrying method employed on site. The incline transported the unprocessed slate up to level 3, and the Maenofferen Upper Mill (NPRN**** now demolished). By the time of the 1st edition Ordnance survey map, a new incline (NPRN ****) was in use, situated in an earlier open cutting to the east of the water balance incline. Around the water balance incline the ground level was raised from the adit entrance on Level 2 up to Level 3, thereby removing the need for the water balance incline and creating a new ground surface upon which the later structures of the quarry were constructed.

References: Plans referred to are held by J. W. Greaves and Sons Ltd, Blaenau Ffestiniog

Louise Barker & Spencer Gavin Smith, RCAHMW, August 2011