Debdon Sawmill and Attached Wall to South West

Debdon Sawmill and the attached wall to the south-west is a powerhouse and sawmill built in the third quarter of the 19th century. The structure is made of snecked rock-faced stone with some cut dressings and features a red clay tile roof. It has an H-plan layout and is mostly single-storeyed, except for the west part of the south wing.

The west elevation is divided into three sections. On the left, the gable end of the north wing has a three-light mullioned window above a round arch for the head goit. The recessed center contains a doorway and a blocked window. The gable end of the south wing on the right features a boarded door under a timber lintel, with a two-light mullioned window above it. The left return has an altered three-light window with two cross windows above. To the far right, there is an attached retaining wall for the approach ramp on the south, which has a heavy flat coping that steps down to the right.

The south elevation is also in two parts. The left part includes boarded double doors in a shouldered arch with a timber lintel, situated under a gablet with a shaped loop. To the right, there is a stepped-and-banded ridge stack, while the lower right part is largely concealed by the approach ramp.

Inside the north wing, there is a Thompson double vortex turbine made by Williamsons of Kendal, which has a maker's plate.

Historically, in 1881, Lord Armstrong connected the turbine to a Siemens horizontal generator, creating the first hydro-electric power source in the world. This power source was used to light the first arc lamps in Armstrong's museum at Cragside, and later, Joseph Swan's newly-invented incandescent lamps.

The building is listed and graded for its historic importance. Adjacent sheds with corrugated iron roofs are not of interest.