17 Gelli-deg

17 Gelli-deg is a cottage within a terraced row, largely altered and dating to the 18th century. The row originally comprised a three-bay house with a small service range set back to the right. The service range primarily belonged to number 15, while the left bay of the house was part of number 16, and six additional cottages were later added in two blocks, now forming the majority of numbers 16, 17, 19, and 21.

The first block of three cottages, now the main parts of numbers 16 and 17, has a painted rendered exterior and a slate roof, with two chimney stacks. One stack is situated between numbers 16 and 17, and the other is at the left end. The eaves and ridge line are higher than those of the earlier building to the right. Originally, each cottage had a single window range, featuring a small window under the eaves and a larger window below, with a door to one side. The first cottage (number 16) has a door to the left of the windows. The other two cottages originally had paired doors between the windows; the door to what was originally number 18 (now part of number 17) has been replaced with a window. Most of the window glazing is 20th-century timber replacing earlier sashes, and the front door is also 20th century. The rear wall is rendered, with two small square windows under the eaves and larger ground floor windows inserted to the left and right.

The interior of 17 Gelli-deg was not inspected during an assessment in 1988. It is likely that the interior would have resembled that of the original numbers 16 and 18. It probably features a one-room plan with access to an upper room via a ladder or steep step. The building has joisted floors with axial joists, and ground floor flagstones.