Corrugated Steel

Emblematic for the other architecture

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.


The only way is: up?

Photo 1. Slum rehabilitation in Andheri West, Mumbai.

A library of considerable size could be filled with all that is written about slum rehabilitation. A seemingly endless number of studies, schemes, plans, proposals, surveys, scenarios, evaluations, and elaborations are made by a similarly endless line of planners, developers, urbanists, architects, authorities, slum lords, students, social experts, economists, engineers, real estate investors, associations, communities, contractors, governments, NGO’s, and so on. The phenomenon is thus big that books (1) are written about it as such, in a variety of qualities (2).

Photo 2. Apartment block towering over Thirteenth Compound, Dharavi, Mumbai.

There is little use in coming up with another plan here. Nor is it doable to explain all strategies being used. This chapter will be limited to how people move from informal settlements to housing and back(!). A short abstract on the mechanisms of rehabilitation is inevitable though.
Slum forming is the result of mass migration into the city combined with too short supply of proper housing. Migrants create their own shelter on whatever space is available, turning the city into a vast campsite. The scale of it leads to incredible densities, leaving little space for the development of adequate housing. Replacing informal settlements by houses, requires a strategy of removing settlers to a temporary location, clearing the land, building new housing, and relocating the settlers into the new building.

Photo 3. Transit camps in Andheri West, Mumbai.

Temporary locations are called transit camps. These transit camps appear in a variety of forms. Some look like stacks of cabins, others mimic apartment blocks. One area in Dharavi, the New Transit Camp, was mainly a handing out of parcels of land allowing people to restart their dwelling-career. By now it is an area of certain urban quality as the inhabitants were able to generate their own housing, upgrading it bit by bit, backed by security of tenure.

Photo 4. Stages of planned redevelopment. Slum on the right, transit camp on the left, construction and relocation in the background. Andheri West, Mumbai.

Photo 5. The demolition of abandoned slum reveals its inner structures. The soil contains an archaeology of the recent past.

Photo 6. As every boy in the world knows, construction sites are perfect playgrounds.

Photo 7. Incremental development (left) and planned redevelopment (high-rise) in Dharavi, Mumbai.

The landscape of Dharavi is permanently changing. In the sea of informal settlements many upgraded houses appear in the user generated process of incremental development. It is a natural process in which end-users change and adapt their environment directly. And thus it will deal will the issue of too high densities as well. It guarantees that every unique need gets its own unique solution. It is the process by which the much loved organic downtown cities throughout the world have evolved. The crucial thing is: this humane process cannot be hastened.
Probably it is the subtlety of this generating process that leaves many using the word slum for areas that are beyond that poor early stage. Moreover, it is spatially intertwined and gradual in time, making it harder to distinguish and appreciate the qualities of incremental development.

Photo 8. Planned redevelopment in Dharavi.

Meanwhile some larger areas are cleared for planned redevelopment and filled in with apartment blocks. More and more blocks are shaping the skyline. As long as there is a piecemeal approach in this kind of development, it has the possibility of adapting and mitigating the worst side effects of high-rise.

Photo 9.Babasaheb Ambedkar Nagar, Parel, Mumbai. Four blocks of low cost housing for former slum dwellers, flanked by high-end apartment blocks and office high-rise.

Building high-rise blocks too close to each other is where many a solution is becoming an enhanced version of the original problem. The cause lies in the scheme by which the project is financed. Authorities allow developers to create profitable high-end housing in exchange for providing housing for the poor, free of costs. This scheme is popular among developers and works quite successful in the sense that it is producing a lot of low end housing. It goes without saying that the land used to create the free housing for the poor, is kept to a minimum. By creating lots of floor area (the essence of high-rise building) the available living space per capita is forced up to the legal minimum. Still the density in terms of land per capita is problematic and sometimes even worsens. Amenities such as infrastructure, transport, commerce, schools, utilities, and qualities like daylight and fresh air are all heavily over utilised.

Photo 10. Babasaheb Ambedkar Nagar seen from Parel railway station, Mumbai. A recipe for vertical slum.

Huge blocks are built only 10 feet apart. The effects on the quality of living are dramatic. Dwellings in the centre of such three dimensional compounds enjoy little daylight and near to no natural ventilation. Not to mention the lack of privacy and the absence of psychological relief by a view from the window. In addition, the images of newly built fresh painted condominiums are deceiving as such no-revenue projects come with a standard lack of maintenance and thus pauperize in a short time. Living on one of the higher floors will inevitably turn out troublesome as elevators are not maintained either, which is a well known reason for not building higher than four or five floors for low income housing. Buildings offering such living conditions are often rightfully categorised as vertical slums. They are the planned version of the City of Darkness (3), the Kowloon Walled City in Hong Kong which was at its peak in the 1980’s home to some 35,000 people on a footprint of only 100 x 200 meters.

The problem of high density is the problem of too little land per capita to begin with. Adding much floor area per capita to it, is of limited help as necessary amenities will claim space outside the building as well. In fact the effectiveness of saving land by adding more floors decreases dramatically between five to ten floors (4) . The popular belief that high-rise is the cure for high population densities, is a myth. As long as there are too many people in an area, there simply are too many people in that area, no matter what fancy way they are packed or stacked.

Photo 11. On the threshold in space and time: brand new housing meets the slum it will replace.

A fair way of grading development strategies is to look at the interaction between user and building.

Only when people contribute, upgrade and improve, the building is a success.
As long as people maintain it, the building is satisfactory.
As soon as it pauperizes, the building is unsatisfactory.
When people move out often, it is a failure.

It is therefore no surprise when inhabitants of rehabilitation projects choose to sell their condo and return to informal settlements. It is a practice often frowned upon, and a show of healthy common sense.

(1) Mike Davis, Planet of Slums, London: Verso, 2006.
(2) Planet of Slums gives an overview of the many programs carried out throughout the world and is a useful book in that way. The downside of the book is its slash-and-burn prose. Not a single program is critiqued positively, not even the demonstrably successful ones. Although Davis presents a plausible analysis of the course of events that led to immense slum forming, he refuses to even hint at a possibility of a way out. He thus takes an easy position. Too easy.
(3) Greg Girard, Ian Lambot, City of Darkness, Life in Kowloon Walled City, Watermark Publications, 1993.
(4) Charles Correa, lecture for Urban Typhoon Dharavi Mumbai, 18th March 2008.


Producing clothes in high quantity is one thing, washing them all is another. Mumbai’s textile industry plays a major role in its economic history. The production of textile in India was boosted by the American Civil war (1861-1865), which interrupted cotton supplies from America to Europe. Great Britain, as the colonizing power in India, was the liaison between Europe and the rising Indian cotton and silk industry. Ever since has the textile industry dominated Mumbai’s development. Many of the old mills are closed now, but the industry is still present throughout the city. A very common sound heard when walking Dharavi, is that of the sewing machines. An endlessly ongoing ‘rrrrrrt… rrrrrrt… rrrrrrrrrrrt’, is the invisible signpost of the ubiquitous workshops.

(Click photo to enlarge)

A familiar sight in Mumbai is the Dhobi Ghat, the open-air laundry. Big ones are located near Mahalaxmi Station. Some two hundred Dhobis (laundrymen) wash clothes here, collected from local households. The clothes are hung out to dry on long cloth lines. The scale of the business is thus big, that it can be seen from afar. It even attracts foreign tourists, leaving the local people in astonishment about what on earth could be so interesting about ordinary laundry.

Except maybe for genuine dry-cleaners, laundry requires water. River banks are good locations for Dhobi Ghats, as are some ponds. Flowing water is essential as stagnant water will be polluted in no time. Step wells, stepped ponds and open tanks, all fed by natural wells, are an important part of India’s water infrastructure. Stepped ponds and tanks are often directly connected to temples and are a place of religious and cultural significance. They symbolise the Ganges; to bathe in such waters is to bathe in the sacred river. With the coming of piped water, many tanks were filled and have vanished under new development. Of all Mumbai’s tanks built in the 18th and 19th century, only two exist today – the Bandra and Banganga tanks. *

In Dharavi a tank-like Dhobi Ghat is located next to the Sion footbridge over the Central Railway tracks. It cannot be missed as the yelling of the Dhobis is advertising the intenseness of the job, much like the sound of professional tennis players. This is where the bigger pieces are treated. Not handkerchiefs and napkins, but heavy blankets and carpets are washed here. Soaked with water they are tossed onto flogging stones. One cannot be but impressed by the labour shown here.

Once cleaned the laundry is put out to dry on the pebble beds along the railway tracks. It is the last remaining open space in the vicinity, by its narrow shape only useful in small plots, it is perfectly exposed to the sun, trains provide frequent blows of wind, and stones to keep it all in place are abundant.

In its way, it is perfect.

*= Neville, Matthew, ‘Banganga. Enduring Tank, Regenerative Tissue’. In: Shannon, Kelly and Gosseye, Janina (eds.), Reclaiming (the urbanism of) Mumbai, Amsterdam, SUN Publishers, 2009, p 112.


Nothing Left Behind

The idea of waste is probably a misconception. In Dharavi virtually everything is reused. The contribution of the recycling industry to the economy is thus big that words like residue and leftover might be trashed themselves. The recycling business provides three major components of economic activities. First, the processing of waste, secondly the supply of raw materials, and third a lot of labour, thus creating livelihood for very many people.

The essence of good reuse is in separation. The more materials are mixed up, the lesser their potential for a second life. Jobs in recycling are therefore mainly concerned with sorting and collecting. Especially sorting is very labour intensive. At the closure of the markets, garbage is sorted into fractions like fruit and vegetables, plastic bags, carboard boxes etcetera.

Biological waste is served as cattle food.

Waste is collected as much as possible on fixed locations. Often a small lot with three walls. Birds, goats, and dogs pick anything edible from and around containers. Textile residues from the fashion industry are used to fire the kilns of the potters.

This waste collection is temporarily out of use. A concrete floor was just cast. Goats are waiting till their familiar spot offers something to eat. Foot prints in the freshly poured concrete illustrate their impatience.

Sorting is very time consuming. While the truck is stuck in a traffic jam, copper wire is picked from electric motors. In the north-west of Dharavi, a whole neighbourhood is busy with recycling. Its name is Thirteenth Compound. One might find it a poetic name. Twelve is considered the number of wholeness, closing many cycles, whereas this hardly known side of our world is the actual closing link in the chain.

Thirteenth Compound is marked by huge quantities of goods stored on its roofs. Whereas everywhere in Dharavi roofs only serve as a protection against the fierce sun and the monsoon rains, the roofs in Thirteenth Compound are the warehouses for light weight goods. Primarily plastics. It weighs near to nothing but is voluminous. The roof is the perfect storage in this dense built area.

The scrap dealer is unloading his truck. Metals are easy to sort as their properties are very diverse. Copper, brass, and bronze have divergent colours. Aluminium is very light weighted. Iron is magnetic whereas other metals are not.

Rusty corrugated steel sheeting, if not for roofing, is used for fa├žades.

Tins and steel jerry cans for food purposes can be sold after cleaning. The future of such a can is destined by its condition. It returns to the original food factory (the spotless), to a manufacturer of something liquid (the second hand), or to a fuel and oil dealer (the slightly crushed).

All packaging materials like barrels and jerry cans are reused and sold. The same applies to cardboard boxes. Spotless boxes are sold back to the factory, already bearing the name of the manufacturer. Boxes in a lesser state are sold to transporter who do not care about the name. Movers, for example. Only worn out boxes are privileged to become raw material for the paper industry.

Amidst the dusty roofs of Dharavi, Thirteenth Compound is an oasis of colours.

Tailor made

Dharavi is not only the destination for those from the countryside seeking the economics of the big city. Mumbai citizens indeed are also seeking shelter after eviction from other locations in the name of redevelopment. Slum areas are demolished to make place for high-rise. Those who lived there are either relocated in transition camps and find new homes in the high-rise, or cannot stay as their livelihood does not allow them to. Many entrepreneurs need a business on street level. Vending only works well on the ground.

The tailor’s shop is about 7 feet wide and 4 feet deep.

The demand for retail space in Dharavi is enormous. A shop of only 4 feet deep, or even less, is therefore already worth exploiting. Vending often begins on a cloth on the street, backed by a blind wall in an alley. A little stall is a step forward. A built shop is the logical follow up.

The tailor’s shop on the left, beginning street vendors on the right.

On top of the shop a floor was created for a room. By extending this floor over the street, more room is created inside. The extra floor doubles as a weather shade, protecting the shop against sun and rain. The shop’s counter can be moved outside, leaving more space inside the shop. Business is perfectly tuned with the spatial dimensions of the shop. No stock is kept here, production is located elsewhere.

In the shop, client’s orders are taken and delivered. All agreements regarding the design are collected in the order book. All sizes of the customers can be found here. Samples mark the chosen fabric. When a customer arrives to collect the order, a staff member walks to the studio to fetch the gown.

Production takes place in the studio on top of the shop. Thus the distance between production and retail is kept very short and efficient. The alley is in close proximity to one of the busiest streets in Dharavi, which is good for patronage.

The shop and the studio are built to a blind wall. That wall is part of a bigger house dating from times this was still a normal fishermen’s village. This story of building to and building upon is typical for the architecture of informal development and slum areas. The forces of society are clearly visible. The owner of the house was willing (or had to be) to allow trading next to his property. The width of the original alley allowed for a stall of only 4 feet. The stall was improved to a built shop. On top of that came a studio, jutting out over the street. Thus the entrepreneur found shelter for his business.

The story of this tailor’s shop is the story of many entrepreneurs in a slum. This is also the story behind the many narrow alleys in slums. Just imagine the tailor’s shop and his studio were not here. We would be standing in a very ordinary street in a very ordinary village.


Of all architectural features, only the roof is essential. The need for shelter, being the most basic need in building, is expressed most clearly by the roof. In relief programs after disasters, provisional shelter is created with tents. A tent is by far the best temporary building as it is purely and essentially: a roof.

For whatever motivation people are migrating, making a roof is the start of settlement. Whether we go out from a luxurious villa to spend the weekend on a campsite, or we go from the countryside to whatever scrap of land available in the big city to build up a living, our putting up a settlement starts with making a roof.

The purpose of a roof is to protect us from the weather. Sun, rain, wind, and cold can all be kept at bay with a roof. A miniature version is the umbrella. If big enough, it will keep us dry as it makes the rain fall in a circle around us. In a crowded situation, the water of our neighbour’s umbrella may fall upon us. Likewise buildings that are directly built to each other, have to deal with rainwater in a collective way.

A proven technique to keep the water out is roof tiling. A roof tile in a sloped position drains the water to one side: the lower. As long as the next tile is below the first, it will do the same and with many roof tiles together, a long path is created to drain the water to the side of the building. Thus, the individual structure of each roof tile is contributing to the accreted structure, the roof. The same principal is used for corrugated asbestos-cement sheeting.

In dense built-up area, such as the informal settlements in Dharavi, an incredible phenomenon can be seen. Not only are individual buildings protected by roofs, made up with the overlapping tile principle. The roofs themselves are in a similar cohesion with the neighbouring structures. Actually, a whole area is protected by putting the roofs in an order that drains the rainwater all the way down to the outside rim. The incredible thing here is that we think such an intricate system can only be achieved through meticulous planning. The informal settlement, considered unplanned, is nevertheless capable of generating such accreted structures.