Slide of RCAHMW colour oblique aerial photograph of Stack Square, Blaenavon, taken by Toby Driver, 2003

Blaenavon Ironworks began production in 1789 and Stack Square was built between 1789-92 to house part of its workforce. It is a U-shaped block of which the south row is known as Engine Row, with a truck shop at the south-west corner. It was originally known as Shop Square but acquired its more recent name when a boiler stack was built in the middle of the square in 1853.

The 2 rows that make up Stack Square incorporate houses of different sizes and status. The east row comprises 5 single-fronted 2-storey houses in reflected pairs, of rubble stone and slate roof. Windows have brick segmental heads and restored 4-pane horned sash windows. At the left end is a lintelled doorway to a separate unit in the angle between the east and north rows, which has a now roofless 2-storey lean-to at the rear. The north row (similar to Engine Row) comprises 4 double-fronted houses of rubble stone and slate roof with later brick stacks. Openings in the lower storey have brick segmental heads replaced small-pane glazing, and all formerly had split boarded doors. Upper-storey windows are beneath the wall plate.

At the rear of the north row is a passage retaining original stone steps at the east end. It has arches across the passage providing buttressing to a retaining wall behind the house. 3 of the house have steps down to narrow back doors, while the north end house has only a small-pane window in the lower storey. The upper storey has a single replaced small-pane window in each house. The rear of the east row has a 2-light replaced casement in the upper storey of each house. The house at the north end has a blocked doorway inserted at intermediate level, while the remainder have segmental-headed 2-light lower storey windows and the house 2nd from the south has an inserted back door. The east row has 2-unit interiors. In the north row the first floors and wooden stairs have been removed, but original fireplaces are retained.