Low - Cost Housing
 

Conventional Methods of Construction
A house, basically, consists of two main structural elements – walls and floors of roofs. Thus, two items including doors and windows, in a conventional house, account for more than 70% of the total expenditure on it.

1. Conventional types of walls
• Mud walls with or without bamboo reinforcement
• Brick masonry walls
• Stone masonry walls

2. Conventional types of floor or roofs
• Thatched roof
• Tiled, asbestos cement or Galvanized Iron sheet roof
• Madras terrace and the allied floors or roofs
• Reinforced concrete or roof

The above types of walls and floors or roofs are not very advantageous on account of one or more of the following reasons:
• Heavy increase in the price of building materials
• Slow and laborious process of construction
• Short span of life
• Expensive maintenance

Various attempts are now being made to devise new methods of construction, which can reduce building costs and also speed up construction, without affecting either the strength or the durability of the building

New Methods of Construction for Low-cost Housing

In recent years, prefabrication of components of houses or complete houses has proved to be the most satisfactory method for reducing the structural and centering materials, construction time and skilled labor required at the site of work. Prefabrication does not necessarily mean mass production, mechanisation or installation of expensive equipment.
Large scale mechanized prefabrication industry will be premature at the present stage of housing efforts in India because India does not have a strong industrial base and the great majority of people live in rural areas which lack good transport facilities. A simple style of prefabrication without the use of expensive equipment or mechanization is the need of the day. It would be possible to affect overall economy in low-cost housing if prefabrication is adopted for the components which are light enough to be handled by few men or a small mobile crane. The manufacturer of the components should be located near the site of the housing project to reduce the transport charges. Also the locally available materials such as soil, stone, lime, fly ash, coal ash, etc. should be used as freely as possible without sacrificing the quality and the strength of the products.

Rammed stabilized mud: For a single storied house, the cheapest wall one can think of is a rammed in-situ stabilized mud wall. It can be built by laying mixture of mud with water and crushed straw into a sliding form and ramming it. Next layer is done after hardening of the previous one. For stabilization it is advisable to add cement or clay. Sliding form is made of timber as a unit about 10’ long. The usual thickness of wall is 10”. The wall can be improved by plastering or white washing.

Soil - cement blocks: These blocks are used in walls varying in thickness from 6” to 12” up to a height of 12’. Soil-cement blocks are made by hand or power-operated machine in a standard unit size of 4” x 8” x 12” and also in three quarter unit and half unit sizes. Soil cement mixtures with minimum compressive strength of 220 lb / in2 and a flexural strength of 50 lb / in2 after 28 days.

Concrete hollow blocks: Prefabricated concrete hollow blocks are made from heavy or light weight concrete can be used for one or two storied houses as bearing walls or multi – storied houses as partitions. Blocks of nominal size 8” x 8” x 16”, also three quarter and half length blocks re produced using wooden or steel moulds by hand or machine. The walls are laid in composite cement lime mortar (1:1:10).

Pillars and panels: The pillar units can be of any suitable size but the most convenient one is 8” x 8” x 12”. Such units can be solid or hollow and are provided with a groove on the sides to receive the panel slabs. They are made in cement mortar (1:6) in the same manner as concrete hollow blocks. The panel slabs are 1 ½” to 2” thick and 12” wide. The length varies with the spacing of the pillars.

Sand Lime/Calcium silicate bricks: Bricks shall be made of finely ground sand/siliceous rock with clay and silt content less than 5% and lime.

Burnt clay-Flyash Bricks: Bricks made of admixture of suitable soils and flyash in optimum proportions. They may be hand or machine moulded.

Pre-cast channel unit for floors and roofs: These are full span pre-cast RCC units-trough shaped in section. These can be used for intermediate floors and roof on suitable supporting structures. They do not require any in-situ concrete over them, nor any intermediate props or supports. The units are strong enough for the full span for which they are designed.

Precast RC planks and joists for floors and roofs: Precast reinforces concrete planks are partially precast rectangular slab elements. These are supported over partially precast RC joists side by side and then joined together and also to the joint by pouring in-situ concrete over the haunches provided in the planks and the gaps between the planks over the joists. Monolithic action of the slab elements is ensured by leaving hooks projecting out of joists and providing reinforcement across the joists over haunched portions of planks, tying them together and pouring in-situ concrete over them.

Thin RC ribbed slab for floors and roofs: Thin RC ribbed slab consists of precast RC ribs 110mmx200mm spaced equidistant at 1200mm centre to centre and 50mm thick cast-in-situ RC flanges. It can be used for floors as well as roofs in buildings. Conventional floor/roof finish can be used above the ribbed slab, as the case may be. Ceiling plaster could be avoided in case of exposed concrete is desired.

Precast concrete waffle units for floors and roofs: The scheme consists of nominally precast open box type concrete units called waffle units laid in a grid pattern and cast in-situ concrete is laid in the joints in the units with the reinforcement provided in the joints. Minimum thickness of top screed is provided depending upon structural and functional requirements. The finished scheme has a pleasant grid pattern in the ceiling. The scheme is suitable for floors/roofs spanning in two directions.

Precast doubly curved shell units for floors/roofs: Pre cast doubly curved or funicular shells in conjunction with precast joists or battens or planks or by providing in-situ ribs in two directions are suitable for floors/roofs in buildings, workshop floors and loading platforms carrying heavy uniform loads.

Precast reinforced prestressed concrete ribbed or cored slab units for floors/roofs: Pre cast ribbed slab units have a thin flange stiffened by longitudinal and/or transverse ribs. Cored slab units are panels in which voids are created in manufacturing process to reduce the cross-section without appreciably decreasing the stiffness or strength. These ribbed or cored slabs are lighter than them normal cast in-situ solid slabs or slab and beam. These units can be used for floors, roofs as well as for wall panels, in residential, public and industrial buildings. These units can be advantageously used for spans up to 9 metres in case of reinforced concrete units and up to 30metres in case of prestressed concrete units with mechanical handling equipment.

Reinforced brick and reinforced brick concrete slabs for floors/roofs: Reinforced brick slab consists of bricks, steel and mortar while reinforced brick concrete slab comprise of bricks, steel and concrete. In case of reinforced brick, the compression is taken by brick while in Reinforced brick concrete, the compression is taken by cement concrete, thus in RB, good quality bricks are required. In later case, the slab can be laid even with low strength bricks. In both cases bricks can be placed either flat or on-edge. RB slab can be constructed with two layers of bricks depending upon the load and span.

Reinforced brick work is practically the same as reinforced concrete in all its essential features except that brick work in cement mortar is substituted for cement concrete.

Prefabricated brick panels for floors/roofs: Prefabricated brick panels are made by a combination of concrete, bricks and reinforcement. These prefab brick panels are placed on partially precast RC joists. The precast joists are supported on walls or beams. Concrete is used in the zone of maximum compressive stresses thus bricks of lower compressive strength may also be used. Further the in-situ concrete, provide over the pre fabricated brick panels helps in designing the supporting partially precast RC joists as T beam. The floor/roof consists of prefab brick panel and partially precast RC joists and in situ concrete.

Ferrocement roofing channels: Ferrocement is thin walled concrete, reinforced with closely spaced layers of galvanized wire mesh. Ferrocement roofing channels are prefabricated, lightweight, slender element shell structures. The standardization of these roofing channesl is based on optimized concrete mix, controlled vibration and dimensional regularity in shape and size.

Precast concrete stone masonry blocks: Concrete stone masonry blocks are made of large size stone spalls bonded together with lean cement concrete mix. q

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