Photo 1. Mexican restaurant in Ebisu, Tokyo, Japan. A welcome natural look between the average contemporary but sterile architecture. Corrugated steel in all its splendour.
Corrugated steel is probably the most iconic of all building materials used in squatter settlements. It is a versatile product as it is strong, watertight, easy to cut, and above all cheap. To many of us, corrugated steel may look ordinary and simple but it is exactly this simplicity which makes it such a brilliant invention. The core of it all is, needless to say, a steel sheet with a thickness of only 1 mm. Such a sheet can be bent or folded in any direction, as a flat sheet has limited stiffness. It is the corrugation which adds the typical structural character. A corrugated steel plate can easily be bent in one direction, whereas at the same time it is very rigid in the other direction.
The production of steel plate is straightforward. Solidified steel bars are rolled until they have the required thickness. Cutting is as easy as cutting paper. Then comes corrugation which requires the most basic of all machines. Let’s say that a classic machine has gear wheels. A corrugation machine would consist of two gear wheels only, nothing more than that. Turning one wheel will automatically turn the other wheel . By feeding a flat steel plate between the two wheels, a regularly corrugated steel plate will appear on the other side of the wheels. The process is beautifully simple.
The resulting wave form sheets are excellent for roofing. Due to their stiffness the sheets need limited structural support. Much like ceramic roof tiles, a limited overlap of sheets will result in a water tight roof. The corrugation prevents leakage to the sides of the sheets.
Photo 2. Corrugated steel in detail, thin like a curtain. Corrosion is typical for re-used sheets.
Steel and water are not exactly friends, which is why steel plates corrode. To avoid this corrosion, steel plates are bathed in molten zinc, a process called galvanising. The zinc keeps the water out and even inverts the corrosion process of steel. Zinc has self healing properties in case of damage of the zinc layer, be it to a certain extent. Galvanised steel can therefore not be bent, under pain of corrosion. This is probably why recycled corrugated steel sheets have a limited life, as in the process of demounting, they are often bent more than is advisable.
Photo 3. Temporary housing for road construction workers. Alibag, Mumbai, India.
The use of corrugated steel for housing has certain drawbacks. Due to its thinness, it has zero insulation capacity, leaving the interior virtually fully exposed to the fierce tropical sun. In the rainy season steel roofs are extremely noisy. It means that corrugated steel creates comfort problems all year round. This is probably why in Mumbai the use of corrugated steel is limited to the temporary housing of construction workers on building sites. Such housing is often provided by the construction company, in which case it is the easiest (i.e. cheapest) material to use. Those people who create their own shelter apparently prefer other materials than corrugated steel. It is something to consider in rehabilitation projects too.
Photo 4. The architecture of the other end. Sheets made in mass production, thought of as a system of repetition, applied in a system-less order.
As the production process is so simple, corrugated steel is ideal for mass production. By its form, it is ideal for covering large surfaces such as roofs and facades, as that would require the least of handling per sheet. This is what distinguishes the architecture of settlements from architectural design. The latter most of the times is an attempt to make something special with materials best used in a system of endless repetition which fails where it meets other systems , whereas settlers are inventive in making something unique with individual sheets, not hindered by any system at all.
The emblematic value of corrugated steel in squatter settlements lies in the fact that it is indicative for the poorest ways of creating shelter and for the poorest ways of offering relief.