Orangi Housing Primer

3. Construction Process

The stone houses in Orangi are mostly self-made whereas the wooden ones are constructed by skilled, hired labour. Stone houses, therefore, are included in the 5 – 7% of houses that are self built in Orangi. In cases where these stone houses are located on the hills, levelling of land is also done by the residents themselves. The construction of a 2 room house takes about a year and is built incrementally over a period of time. If the land is to be levelled as well, then in the absence of hired labour, construction may be completed anywhere between 1 to 2 years. The cost is very little since labour and material are not paid for. In most cases bonding between the stones and plastering either by mud or mortar, is missing. Houses which have walls bonded and plastered, even by mud, have a longer life and withstand higher climatic pressures.
Wooden houses mostly fall in the category of 55 – 60% of houses which are built with the help of skilled labour. The material of construction is obtained from scavengers and junk yards that sell scrap wood. These houses comprises of a single 8’ x 12’ room with an open kitchen, bathroom and courtyard around it. (See photograph 26). The cost is usually between Rs 3,500 – Rs 4,000 and it takes about a week to construct such a house. This does not include the time required for levelling land. If land is also leveled by hired labour then the cost can be as high as Rs.7000 per house and it can take as long as a month to complete.

4. Problems in Construction

4.1 Technical Problems

4.1.1 Stone Houses

The un-bonded foundations and walls of the stone houses are essentially weak and offer no resistance to wind forces. In the recent dust storm of May 31, 1986 these houses suffered from severe damage and in many cases had to be reconstructed by the owners. The uneven settlement of the foundation stones also causes cracks in the walls. The mortar used for bonding of the stone is weak as better quality mortar is usually too expensive for the owner. The locally available mud has almost no clay content and as such is easily washed away by rains. This added to the unevenness of the stones, renders the walls weak.

The galvanized iron sheet roofs leak and rust due to:

• Incorrect longitudinal and transversal overlapping;
• Inappropriate slope given to the roof which results in collection of rain water and eventual seepage into the walls. Due to the absence of eaves water flows over the walls and washes off the mud used for bonding and plaster.

In addition, the sheets are not tied to the girders and the weight of the blocks placed to hold down the roof is insufficient. This results in roofs being blown off by strong winds. Similarly, the reed matts are not tied properly to the trusses and also result in leakage and vulnerability to storms.

4.1.2 Wooden Houses

The construction of wooden houses is done by “mistris” (builders). The quality of wood used is very poor due to economic reasons. The wood is untreated scrap wood obtained from scavengers and junk yards. The houses are therefore, subject to attack by termites, water and fire.

In cases where tiled roofs are used, the roof trusses are too weak to bear the weight of the tiles arid often sag. The problem in this case is primarily poor construction and joinery. The only joinery detail used is nailing with no other use of steel connections or joints.(See photograph 27 & 28).

5. Sociological Problems

The major problem that the inhabitants of stone houses reported, was difficulty in procurement of stones as a building material. In the absence of proper tools and hired skilled labour, owners of the houses have to rely on themselves to quarry and transport stone from the nearby hills. This results not only in a long construction period but also limits the location of the houses to the foot hills of Orangi. (See photograph 29).

The owners are usually not familiar with the art of constructing wooden houses. This results in inadequate management of the mistri’s work by the owners and therefore, poor construction. In addition, wooden construction is not very common in Karachi, with the result that well trained personnel are not available.

6. Economic Problems

A large part of the problems of construction in wooden and stone houses is a function of the economic conditions of the owners. Quality of wood, absence of bonding and plaster between stones etc are a few examples. However, remaining within the economic constraints of the situation technical solutions can be proposed which can greatly improve the technical quality of stone and wooden houses.

III. Pucca Houses

1. Description

Pucca houses are the most permanent structures in Orangi, capable of resisting the forces of climate. However, their construction can be greatly improved through better use of materials and improved construction technique.

1.1 Foundation

Pucca houses, as they are presently constructed, have three types of foundations:

• Stone Foundations.
• Cement Block Foundations.
• RCC Foundations.

1.1.1 Stone Foundation

Stone work in the foundations of pucca houses is similar to the stone used in katcha and semi-pucca houses. The most common way of constructing a stone foundation is to dig a ditch 2½’ deep and 1’ to 1½’ wide. This ditch is filled with stones and compacted, over which the wall is erected. Where digging is not possible, a stone foundation is construction on top of the ground 8” – 12” high. In some cases the stones are held together by mortar whereas in others mortar is altogether absent (see photograph 30 & 31).

1.1.2 Cement Block Foundation

In this type of foundation the ground is dug 1’ to 1½’ deep and 1½’ wide. A bed of stones ballast is laid in the excavation followed by a bed of mortar. Cement blocks are placed on this mortar bed which form the foundation, over which a cement block wall is constructed.

1.1.3 RCC Foundation

RCC foundation is the most stable form of construction which is able to support two or more stories.
For a RCC foundation, ground is dug, usually 3’ deep and a concrete pad of 1:4:8 ratio poured over it. Shuttering is then placed along with horizontal and vertical reinforcement and concrete poured in. After the concrete is set, shuttering is removed and the structure cured for 2 to 3 days. If load bearing walls are used then the foundation is continuous, whereas, in certain wall construction RCC foundation is placed only under columns (see photograph 32).

1.2 Walls

Walls of pucca houses are made of cement blocks. The walls are of two kinds, namely:

• Load Bearing Walls.
• Non-load Bearing Walls.

1.2.1 Load Bearing Walls

Load bearing walls bear the entire weight of the structure. The cement blocks are available at the “thallawalas” in two sizes viz 4”x6”xlO and 6”x8”xl2”. The size of the actual blocks is usually slightly smaller, in an effort to economise on the use of material by “thallawalas”. Load bearing walls are characteristic of non-RCC construction and are usually left un-plastered (see photograph 33).

1.2.2 Non-Load Bearing Walls / Curtain Walls

Curtain walls are a characteristic of framed structures. The walls do not bear any load. The entire load is borne by beams and columns, which are made of reinforcement concrete (see photograph 34). Almost always a RCC construction is of a frame structure and walls are plastered. Size of the column and beam is dependent upon the span of the structural members. The sizes of the concrete blocks are the same as described above and procured from the “thallawalas”. If the economic condition of the owner allows, then blocks can be also constructed at the site.

1.2 Roofing

Two types of roofing material are used in pucca houses

• Corrugated Asbestos/G.I. Sheets.
• RCC Roofing.

1.3.1 Corrugated Asbestos / G.I. Sheets

Asbestos/G.I. sheets are usually used in houses which do not have RCC construction, but make use of stone or cement block foundation. Reason for this is the economic constraint of the owner. Method of construction of asbestos roofing is similar to that of semi-pucca and katcha houses. Ends of the sheets are overlapped 3’ – 6’ and placed over beams made of either concrete, steel or wood. The sheets are held down with the help of concrete blocks placed at the perimeter of the roof (see photograph 35). Choice of material for the beam is also dependent upon the economic condition of the resident.

1.3.2 RCC Roofing

Reinforced concrete roofing is mostly used in frame structures, where the load of the structure is borne by columns and beams after the columns have been erected and reinforced concrete beams placed on the columns, shuttering is placed to provide temporary support to the roofing. A net of reinforcement is placed over the shuttering on the beams and columns before concrete is poured to form the roof slab. After the concrete roof slab has set, shuttering is removed. Load of the roof is borne by beams and transferred to the columns. These roofs are flat and if the foundation is appropriate, a second storey can also be built (see photograph 36).