Section of roof at Ulster Carpet Mills, Castle Island Factory, Garvaghy Road, Portadown, Co Armagh, BT62 1EE

Small section of Belfast Truss roofing belonging to a building of approximately the 1920s, now almost completely submerged within the middle of a very large carpet factory complex. The factory is set on the north side of Garvaghy Road, to the north-west of the centre of Portadown. The section of roofing belongs to a building which was probably originally either free-standing or partly exposed to ground level, but which can only now be seen as a portion of roofing set within a vast factory complex. The factory itself appears to have grown to its present size over many years and consequently displays various different types of building styles and roof construction.

The section of roofing itself measures roughly 10.5 metres by 7.5 metres and is covered in corrugated metal with what appears to be a circular vent projecting through it close to the eastern end. Below the roof, on the north side, there is a small section of exposed façade which is in brick with large areas of glazing. The small section of the exposed west gable appears to be rendered. The exposed portions of the east gable and south elevation could not be seen, however internal evidence shows that there is a row of windows to the south similar to those to the north.

The Belfast truss was developed in the mid-nineteenth century to meet the demand for efficient, lightweight and long-span roofs brought about by the industrial revolution. The first known reference to a curved wooden felted roof structure supported by bowstring girders is in an advertisement in the Dublin Builder for 1866 by the Belfast firm of felt-makers, McTear & Co. McTear's continued making trusses until they went out of business in 1908. A second Belfast felt supplier, Anderson & Co., began to produce trusses, to a slightly different design, in 1886. In 1896, Anderson's launched their Mark II version, promoted as maximising long spans whilst maintaining light weight. This model was subsequently used by other companies, and is referred to by historians as the Belfast truss, although this term is widely used to apply to all timber bowstring trusses where the internal bracing members meet not on the bottom of the truss as was the convention but on the top curved member. This section represents a good intact example of a Belfast Truss roof, although its impact has been negated by the virtual disappearance of the building to which it belongs.