Metal-framed windows are so ubiquitous in modern buildings you hardly notice them, but that hasn't always been the case. A 500-year process of technical refinement has seen metal window frames go through a variety of permutations, from easily-stolen lead to classical wrought iron and modern aluminium, writes Colin Bisset.

In theory, using metal for window frames is a perfectly rational use of the material. A metal frame is, after all, rigid which means the glass it holds won't flex and crack. It’s also a temperature conductor, though, and that can lead to condensation issues. Perhaps this is the reason why it has taken so long for it to be accepted into our homes.

Gazing out of a building is more complicated than you might think, but the refinement continues.

Lead was used in the earliest window frames thanks to its softness. It easily wrapped around a sheet of glass (and was easily unwrapped by thieving hands, too). A famous example is the mullioned facade of Britain's 16th century Hardwick Hall—'more glass than wall' as it was popularly described.

Timber frames became popular in both Britain and the Netherlands in the 17th century as timber buildings were replaced by stronger brick and stone structures with wider window openings. The sash window also referenced the fine lines of neo-Classicism, popularised by Inigo Jones after his encounter with the villas of Palladio in Italy. After London's Great Fire in 1666, wooden sash windows became mandatory.

The old-style metal frame, however, had its followers. The traditional look of a wrought-iron frame was especially popular with Arts and Crafts architects like Voysey and Webb, who liked the contrast of a metal frame against stone or brick mullions. They referenced a slower age, away from mass-production, but it meant that large window openings were still filled with smaller individual frames.

As glass-making techniques improved and modern steel was invented in 1855, larger windows were possible in frames that had none of the brittleness of iron. It was soon the favoured material for windows in factories, office buildings, schools and hospitals, thanks mainly to its fire-resistance, but the rational look made it unpopular in domestic situations. Until, that is, the beginning of the 20th century.

Early Modernist architects liked metal frames’ graphic lines and the industrial aesthetic, as well as their ability to hold such large panes of glass. Peter Behren's groundbreaking AEG Turbine Hall of 1908 showed cathedral-like glass windows framed in metal. Metal frames were also demonstrated in the astonishingly light curtain-wall windows of Walter Gropius' Model Factory of 1911 and the Fagus factory of 1914. By the 1920s, most architects wanted sizeable windows for their domestic projects—sunlight was being newly appreciated as healthy and hygienic.

In Britain, window manufacturer Crittall produced a range aimed at both the modern and traditional markets. Their modern styles were showcased in a housing development for their own factory workers designed by Thomas S. Tait in 1926.

Problems continued to dog the metal frame, however, especially when coupled with ever-increasing areas of single glazing, such as in Mies van der Rohe's spectacular Farnsworth House of 1946, whose windows were often covered with rivers of condensation. He went on to use bronze-framed windows in his office buildings as glazing techniques improved, giving rationalism a hefty dose of swank.

In the 1940s American designer Buckminster Fuller introduced the first of his geodesic domes, structures that were lightweight and strong, made entirely of glass panels held within a frame of aluminium tubing, just as aircraft used. As the material became more available the way was paved for metal frames to reach a wider audience. Crucial to their popularity was the addition of a rubber seal as a thermal break and the introduction of double glazing. Today, virtually all commercial buildings and 75 per cent of houses in Australia use aluminium framed windows, often powder-coated to give them a more traditional look.

Other materials are being used for frames, too. Unplasticised PVC is popular in Europe and gathering fans in Australia thanks to the same qualities of strength and affordability, although design aficionados have long disparaged them for their fakery. Fibreglass frames are also strong and light and have few issues with temperature conductivity. The frameless window made its appearance in homes during the 1990s, although commercial buildings had been experimenting with glued glass windows since the 1970s.

Gazing out of a building is more complicated than you might think, but the refinement continues. So where next—carbon fibre?

By Design looks at the places and things we imagine, build, use and occupy, explaining how creative ideas take tangible form through the design process.



