Low cost house construction

Adequate shelter for all people is one of the pressing challenges faced by the developing countries. India is currently facing a shortage of about 17.6 million houses. The dream of owning a house particularly for low income and middle-income families is becoming a difficult reality. Hence, it has become a necessity to adopt cost effective, innovative and environment-friendly housing technologies for the construction of houses and buildings for enabling the common people to construct houses at affordable cost. Strength and durability of the structure, stability, safety and mental satisfaction are factors that assume top priority during cost reduction. It is found that about 26.11% and 22.68% of the construction cost can be saved by using low cost housing technologies in comparison with the traditional construction methods in the case studies for walling and roofing respectively. This proves that using low cost housing technologies is a cost effective construction approach for the industry.

Importance of low construction

Low cost housing is a new concept which deals with effective budgeting and following of techniques which help in reducing the cost construction through the use of locally available materials along with improved skills and technology without sacrificing the strength, performance and life of structure.

In developing countries such as India, only 20% of the populations are high-income earners, who are able to afford normal housing units. The low-income groups in developing countries are generally unable to access the housing market. As housing demand in India is continuously growing, different government schemes are being implemented to cater to the need of mass housing for the poor and lower income group people. So that mass housing can be done in a low budget through appropriate Cost effective Eco-friendly Construction Technologies (CECT). The reduced cost of building, enhancement of comfort level and non-compromise on safety may establish appropriateness of CECT, which will also act as a market force and demand for such technologies is expected to grow up.

It should be noted that low cost housings are not houses which are constructed by cheap building materials of substandard quality.
A low cost house is designed and constructed as any other house with regard to foundation, structure and strength.
The reduction in cost is achieved through effective utilization of locally available building materials and techniques that are durable, economical, accepted by users and not requiring costly maintenance.
Economy is also achieved by postponing finishing and implementing low cost housing technologies in phases. High efficiency of workers, minimize waste in design and apply good management practices, can also be achieved.
Low cost housing technologies aim to cut down construction cost by using alternatives to the conventional methods and inputs. It is about the usage of local and indigenous building materials, local skills, energy saver and environment-friendly options.

Low cost building technologies

The general economy in the construction of a house can be achieved by:

Proper layout
Proper selection of materials
Better structural designs and
Speedier and economical construction methods Before presenting the new techniques in building construction, it may not be out of place here to give a brief account of the conventional methods of construction adopted in this country.

Traditional construction methods

The traditional construction methods are used in the case study. The detail procedures of each step used for the case study are as follow:

Foundation: Foundation is the lowest part of the structure which is provided to distribute loads to the soil thus providing base for the superstructure. Excavation work is first carried out, then earth-work is filled with available earth and ends with watering and compaction in a 6” thick layer.
Cement concrete: Plain cement concrete is used to form a levelled surface on the excavated soil. The volumetric concrete mix proportion of 1:4:8 (cement: sand: aggregate), with a 6” thick layer for masonry foundation and column footings is used. Plain cement concrete is finished on the excavated soil strata and mixed by manual process.
Wall construction: Size stone masonry for foundation is constructed for outer walls and burnt brick masonry of a 9” thick layer for main walls and a 4 ½” thick layer for all internal walls. Good quality table-moulded bricks are used for the construction.
Reinforced cement concrete slab and beam: The normal procedure to cast reinforced cement concrete slab is to make shuttering and provide reinforcement and concreting. Good steel or plywood formwork is used, with proper cover blocks between bars. Both aggregate and sand used are clean, with aggregate being ¾” graded. After the concrete is poured, it is properly consolidated.
Plastering: Plastering is used for the ceiling, inside and outside walls. Joints are raked before plastering and proper curing is ensured.
Flooring: For the flooring purpose, the earth is properly filled and consolidated in the ratio of 1:4:8 (cement: sand: aggregate) concrete.
Plumbing: Good quality plumbing materials are used and passed hydraulic test before using it.
Painting and finishing: Before the painting process, surface is prepared with putty and primer and readymade paint is used.

Low cost construction technologies:

It is found that cost-effective and alternative construction technologies, which apart from reducing construction cost by the reduction of quantity of building materials through improved and innovative techniques, can play a great role in providing better housing methods and protecting the environment. It should be noted that cost-effective construction technologies do not compromise with safety and security of the buildings and mostly follow the prevailing building codes. The detail procedures of each step used for the case study are as follow:

Foundation: Arch foundation is used in which walls are supported on the brick or stone masonry. For the construction of the foundation, the use of available materials such as brick or concrete blocks can be made to resist lateral forces buttresses at the corner.
Walling: Rat trap bond technology is used in the case study. It is an alternative brick bonding system for English and Flemish Bond. The reduced number of joints can reduce mortar consumption. No plastering of the outside face is required and the wall usually is quite aesthetically pleasing and air gaps created within the wall help making the house thermally comfortable. In summer, the temperature inside the house is usually at least 5 degrees lower that the outside ambient temperature and vice versa in winter. Also locally available and green materials can be used for walling.
Roofing: A filler slab roofing system is used which based on the principle that for roofs which are simply supported, the upper part of the slab is subjected to compressive forces and the lower part of the slab experience tensile forces. Concrete is very good in withstanding compressive forces and steel bears the load due to tensile forces. Thus the low tensile region of the slab does not need any concrete except for holding steel reinforcements together.
Flooring: Flooring is generally made of terracotta tiles or colour oxides. Bedding is made out of broken brick bats. Various patterns and designs are used, depending on shape, size of tiles, span of flooring, and client’s personal preference.
Plastering: Plastering can be avoided on the walls, frequent expenditure on finishes and its maintenance is avoided. Properly protected brick wall will never lose its colour or finish.
Doors and windows: As door and window frames are responsible for almost half the cost of timber used, avoiding frames can considerably reduce timber cost. Door planks are screwed together with strap iron hinges to form doors, and this can be carried by ‘holdfast’ carried into the wall. The simplest and cost effective door can be made of vertical planks held together with horizontal or diagonal battens. A simplest frameless window consists of a vertical plank of about 9” wide set into two holes, one at the top and one at the bottom. This forms a simple pivotal window. Wide span windows can be partially framed and fixed to walls or can have rows of pivotal plank

Cost effective and eco-friendly construction practices

methods of construction for low-cost housing: –

Analysis of Applicability and Availability

In recent years, prefabrication of components of houses or complete houses has proved to be the most satisfactory method for reducing the consumption of structural and centering materials, construction time and skilled labour required at the site of work. Prefabrication does not necessarily mean mass-production, mechanization 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 the 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 a few men or a small mobile crane.

The manufacture 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.

Forms of foundation:

Random rubble masonry
Stones are sustainable and reuse in later stage life expectancy of building. Foundations are the lowest part of building, so below ground level dry pack is provided unless it is not a water logged area. Otherwise RR with CM 1:6 is provided for foundation and basement.
Solid block masonry
Solid block with CM 1:6 is provided for foundation and basement.
Strip beam foundation
Made up of reinforced cement concrete in 1:2:4 or brick masonry with CM 1:6. It consists of footing and pedestal.
Arch foundation
Inverted arch foundations are provided in places where SBC of soil is low. Inverted arches are constructed between the walls.

Forms of walls:

Rammed stabilized mud
For a single-storey 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 25 cm long. The usual thickness of wall is 25 cm. The wall can be improved by plastering or white washing. Strength largely depends in stabilization process and degree of stabilization. So not trustworthy.
Solid block masonry
These blocks are used in walls varying in thickness from 6″ to 12″ upto a height of 12′. Soil-cement blocks are made by hand or power-operated machines 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 optimum moisture content are selected to give a minimum compressive strength of 250 lbs/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- storeyed houses as bearing walls or for multi-storeyed houses as partitions. Blocks of nominal size 8″ x 8″ x 16″, also three-quarter and half-length blocks are produced using wooden or steel moulds by hand or machine. The walls are laid in the conventional way using composite cement lime mortar (1:1:10).
Pillars and panels
IThe 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 1/2″ to 2″ thick and 12″ wide. The length varies with the spacing of “the pillars. The concrete mix used is (1:2 1/2: 3 1/2) and the reinforcement is 1/4″ bars longitudinally and 1/8″ bars transversely at 8” centers. These units are made in simple wooden or steel moulds.
Precast panels (UCOPAN)
These panels have been designed and standardized by the Calcutta Metropolitan Planning Organization. The panels are 1 1/2″ thick and have two sizes 3′ x 9′ for walls and 3′ x 10′ for floors and roofs. Different types of wall panels with voids for doors, windows, ventilators or solid ones can be manufactured in a single-type universal form by using replaceable inserts wherever necessary. The panels have a mesh reinforcement consisting of steel bars of diameters 1/8″, 3/16″, 1/4″ and 5/16″. They have ribs 8″ in depth which serve to provide the rigidity needed. It is suitable for house colonies as well as places where transportation is easier i.e. access for cranes to the site.

Forms of roofs:

Precast T-beam type
This roof system is very simple and easy to construct and has been successfully used on a number of constructions in India. It is of two types – ordinary and hollow. For all spans, these units have a uniform flange width of 12″. The depth of the rib and the reinforcement are adjusted to suit the span. After units are set in position, the joints are grouted to make them water-proof, with cement mortar (1:2), mixed with 10 % of (by weight of cement) crude oil. The hollow type of roof, although more expensive, provides better heat insulation and also has the added advantage of better appearance due to flat ceiling. The T-beam units are cast in simple moulds either of wood or steel. If the number of units required is small, an adjustable mould can be made to make T-beams of different depths. Some of the disadvantages of such forms of roofs are they are heavy members which results in difficulty in connecting the members as well as weak in resisting lateral forces.

Composite T-beam type

Composite I-joist-slab type

Forms of Stairs:

The conventional method of constructing a staircase is cast-in-situ which is constructed by providing formwork and concreting during the initial stages of construction. However this type of construction has proved to be expensive when compared with precast stairs. The riser and tread of such stairs will be 15cm and 25cm for residences. Precast stairs are cheaper and quicker to construct. It does not require any formwork thus reducing the labour charges as well as shuttering expenses. Such stairs can be cantilever or simply supported. Cantilever is more suitable for low cost construction but simply supported is more durable.

Forms of door and window frames:

Since good seasoned wood is not easily available except at exorbitant prices, substantial savings in cost can be affected by replacing the timber frames of doors and windows by those of reinforced concrete. They cost about half the price of country teakwood and are becoming increasingly popular, especially for low-cost houses.

The other types of window and door are given below:

Aluminium window frame and shutter
Steel window frames and shutter
Readymade skin door
Steel door
Fibre door
PVC door