The Pentrebach Triangle was a planned settlement of fifty-four houses constructed in the 1830s and 1840s, in association with the development of the Pentrebach Forge (NPRN 91544) by the Hill family of Plymouth Ironworks (NPRN 34114). It comprised four rows of double-fronted terraced houses, two of them facing each other across Church Street (which was part of the Merthyr - Cardiff turnpike road to c1840 when a new alignment was laid out to the west), and two rows enclosing a triangular space to the west of Church Street. The houses had two rooms and a pantry on the ground floor, and two rooms above, accessed by half-spiral stone stairs built into the very thick party walls between alternate pairs.
By 1813 there was already a row of terraced housing, Long Row (NPRN 408965) , to the east of Church Street, and a building on the east side of Church Street itself, possibly an alehouse which was later converted to four houses. Further building of Triangle probably began in the late 1830s, with two stages of six houses each on the east side of Church Street, attached to the south end of the alehouse building. The first seven houses of the south row (from the east end) of the Triangle probably also date from this period. The later houses used greyish-yellow bricks for window arches and chimneys. All were built by 1851. At first there were no back doors, and all had small enclosures at the front, some of which contained sheds for coal. Water came from a pump and trough in the centre of the triangle, and a block of four privies was constructed behind the south-west corner. Later many of the houses acquired single-storey rear extensions.
The houses were Listed Grade 2 in February 1975, but had already been earmarked for clearance. They were demolished on 12 December 1977, and the whole site and all related landscape features have been obliterated by the building of large industrial units.
W J Crompton, RCAHMW, 10 December 2009.