Iron, Lead and Steel

Iron

Iron can be used functionally in the construction of a building and decoratively for its adornment. The simplest building element, and one that is found in Antiquity, is an iron nail. Iron can be used as structural reinforcement; as a shoe to hold the end or a clamp to tie the lengths of a timber beam together; it can be uses as a rod to increase the tensile strength of a roof truss or to provide additional structural rigidity as a tie between the walls of a large warehouse. In this case iron plates or bosses, usually circular or oval in form, will appear on the exterior walls of the building.

Iron often lies hidden in masonry. In harbour walls and where a fine stone facing is applied to a building metal clamps will have been used to hold the different parts of the structure together. In modern times this often leads to conservation problems. Over the years water penetration rusts the clamps which then expand forcing semi-circular pieces of the stonework to flake off the wall surface.

From the middle of the eighteenth century the technique of casting iron into moulds was developed. This permitted the multiple production of highly decorative patterns at little cost and had an immediate effect on the elaboration of railings, balconies and street furniture. It also led to the development of innovative cast iron constructions such as the Halfpenny Bridge, erected over the Liffey in Dublin in 1816, and the glass and cast iron Green Houses at Glasnevin, begun in 1843.

Lead

Lead is a soft metal which melts at a comparatively low heat. It is malleable and can be formed into sheets that may be folded over parapets and round corners. These properties mean that lead is often used as a 'flashing', an impermeable membrane that prevents water penetration at the point where two parts of a building are joined together. Lead flashings can been seen where chimneys project through roofs, or round the sides of dormer windows. Lead is often used to line a gutter behind a parapet and may be carried over the top of the parapet as a flashing to the top of the stonework. In foundations it was often used, before the invention of bituminous felts, as a damp proof course to prevent moisture rising through the masonry of a wall.

Lead's most obvious role in buildings is as a roofing material. This occurs when the slope of the roof is too shallow to allow it to be safely covered in slates or tiles. There is a limit to the size of lead sheet that can be made and, because of this, roofs to be covered in lead are made of a number of sheets. The sheets are joined together by folding the side of each sheet over a timber roll with one sheet overlapping the other. At the top and bottom the end of the sheet are folded one inside the other, folded a second time, and hammered flat. This allows for rainwater to flow over the sheets in a controlled way. The rolls give a lead roof an unusual ribbed effect which can be used decoratively. Complicated architectural forms such as domes and spires are often covered in lead.

Steel

Steel frame of the Savoy cinema in Dublin

This is a photograph taken during the construction of the Savoy Cinema in Dublin, showing how the steel is used as the construction frame for the building.

Irish Architectural Archives

Steel frame of the Savoy cinema in Dublin
Irish Architectural Archives

Steel frame of the Savoy cinema in Dublin

This is a photograph taken during the construction of the Savoy Cinema in Dublin, showing how the steel is used as the construction frame for the building.

Irish Architectural Archives

Enlarge image

Steel is a form of iron with a low carbon content and very small amounts of other elements such as silicon, manganese and, for special steels, chromium, nickel and aluminium. Steel is strong in both tension and compression but distorts at high temperatures, and (except for special steels) it is subject to rusting. Consequently steel has to be given fire-proof cover, and also has to be carefully painted in many circumstances.

In contemporary architecture steel is frequently employed to provide a structural frame for a building which is assembled out of extruded steel H-shaped beams and columns, bolted or welded at junctions. The architecture of most modern skyscrapers relies on the structural capacity of these steel frames to withstand all probable loads, including those arising from wind and earthquake. Architects can choose to express the steel structure in the style and elevations of the building, or to disguise the structural elements in some form of cladding.