Walking through any of Europe’s capital cities offers quite a record in how radically the direction of the styles of building facades has changed even during the last century.
Cladding of building facades
It is not unusual to see a variety of building facades on anything from local authority buildings, through airports and hotels, to concert halls and town houses with flats and balconies – no two neighbouring buildings are the same.
The most common materials used for cladding on modern city builds are steel, stainless steel and aluminium. All of them have their advantages in terms of providing a high quality, sustainable and cost-effective exterior. For example, stainless steel’s glossy finish makes it a highly attractive option for any built structure were the aesthetics of the result are important, and its self-healing properties are ideal for minimising maintenance costs. Stainless steel cladding is both a sustainable and cost-effective choice for buildings that need to last.
Aluminium cladding generally has a neoprene core, making it the ideal choice for buildings where energy efficiency is of prime importance. Aluminium is also useful for its lighter weight.
Thanks to particular techniques, we can colour both metals to match the architect’s design.
When it comes to structural elements like in building facades and curtain walls, the material must carry the weight of glazing and withstand the force of the wind. This makes material choice a balance between structural demands and artistic design.
Aluminium – the light solution
- Architects prefer aluminium for skyscrapers with glass panels. One cannot beat the price advantage and the design flexibility – as long as it has limited dimensions.
- The reduced weight of this material helps to contain overall structure costs of the building.
- We can brush or polish aluminium for glossy and appealing surface.
- It is also a very good heat conductor, so constructors very often use it in order to dissipate heat like in car radiators and air conditioning units. But the use for frames for glass panels calls for expansion joins that compensate the significant thermal expansion due to the solar heat.
- This material also has an element of corrosion resistance unless the environment is highly acidic; then it can corrode at a potentially catastrophic rate.
For all these reasons, Aluminium is a good choice for limited frame sizes like the height of the building’s floors.
Steel for large glazing portions
- Designer and builders most commonly use steel large curtain walls, the main entrance where lots of light shall come in.
- The mechanical yield of the material allows the design of significant glazing portions with wide spans and heights up to more than 15 meters.
- The design is much less flexible as for aluminium sections that we can extrude to almost any shape. With steel, we would need to machine complex shapes.
- One downside of steel is that the surface must be treated against corrosion, like zinc coating or painting. Possible scratches might affect the surface protection resulting in rusty zones if not repaired.
- Steel is a very ductile material and welding is an easy and common process that can be performed on site
Stainless steel comes with almost same advantages of steel
- Stainless has a slightly reduced yield strength compared to common steel, but anyhow nearly three times the values of aluminium.
- This allows wide spans and high curtain walls, granting the maximum possible light inlet.
- Stainless steel is corrosion resistant. It is a melt of iron, chromium, nickel, and other precious metals like molybdenum. Furthermore, stainless steel has mild self-healing properties, making it the first consideration where corrosion might cause issues with the build.
- Like aluminium, stainless steel is available with different surface finishes. For transom and mullion constructions there is a standard finish that is grit shot blasted. However, prestigious projects demand for prestigious surface finishes. They range from brush finish, to satin polish finish, ending up with the high-end mirror polish.
- As for steel sections, those will seldom find application in glazing support of short portions of buildings. Only where the structural properties of aluminium will not match it.
Of course, there is no reason why one cannot use the two materials in conjunction with each other. Especially where the strength of a steel frame in tandem with the lightness of aluminium cladding provides the best and most cost-effective structural solution for the main contractor and client it makes sense to use them together.
Both aluminium and stainless steel have relative merits which depend on the end use. Stainless steel takes the honours for prestige, durability and strength, such as the glass walkway in The Basilica of Aquileia in Italy, the cladding of the Paul Klee Centre in Berne, and the space-age and spacious stations of the Jubilee Line extension on the London Underground.