LOW COST CONSTRUCTION

TECHNIQUES
Low cost construction is not always low cost
housing for poor but it is cost effective
construction techniques.

Cost effectiveness
Economics are dependent on very diverse factors, some of which
are not within local control. But certain factors can be controlled
by the local area for the enhancement of the local economy.
•Less outflow of money and other resources by the adoption of
certain technologies and materials
•Creation of employment by up-gradation of local skills
•Innovative use of the available building materials
•Direct market and supply connection - elimination of the
middleman
•Labour intensive approaches
Sustainable technologies, use of renewable energy sources is
also very much part of low cost construction.

It includes-
Traditional construction technologies like-Earth construction
-compressed earth blocks
-Rammed earth technology
-Rat trap bond wall
-Filler slabs
-Brick arches and vaulted structures.

Advanced technologies include-

Ferro cement technology.
Earth construction-
Raw earth for building has been used worldwide for millennia but during the 20th
century most of the skills of earth builders were lost and building with earth became
marginal.
Most of the projects are built with compressed stabilised earth blocks (CSEB), as this
technology benefits of more than half a century of research and development
worldwide. Stabilised rammed earth is also used
extensively for foundations and to a lesser extent for walls. In Auroville, CSEB present
several advantages compared to the local country fired bricks:
• Walls made of CSEB and stabilised rammed earth are always cheaper than fired bricks.
• The initial embodied energy of CSEB produced on site with 5 % cement is ~ 4 times
less than the local country fired bricks.
• The strength of these blocks is most of the time higher than the local country fired
bricks.
There are also three other earth techniques used in Auroville. These techniques are very
marginally used as only about 10 buildings have been built with them:
• Raw rammed earth
• Adobe blocks, the traditional sun dried mud brick
• Wattle and daub which is mud plastered on a wattle made of split bamboo or palmyra
tree
APPROPRIATE BUILDING TECHNOLOGIES BASED ON
EARTH
The main research and development is focussed on minimising the use of steel,
cement and reinforced cement concrete (RCC). Most of the technologies
developed have now been mastered and the present
The building is constructed entirely with stabilised earth, from the foundations to
the waterproofing:
• Stabilised rammed earth foundations (with 5 % cement)
• Stabilised rammed earth walls (with 5 % cement and a “homeopathic” milk of
lime and alum)
• Composite columns (round and hollow CSEB with reinforced concrete)
• Composite beams (U shape CSEB with reinforced concrete)
• Stabilized earth mortars and plasters
• Wide variety of compressed stabilised earth blocks (17 moulds are presently
available for producing about 75 different types of blocks)
• Various vaults with compressed stabilised earth blocks
• Alternative stabilizers to cement (“homeopathic” milk of lime and alum)
• Alternative waterproofing with stabilized earth (various mixes of soil, sand,
cement, lime, alum and juice of a local seed)
COMPRESSED STABILISED EARTH BLOCKS
CSEB is nowadays the earth technology, which is the most used
worldwide, as well as in Auroville, because it represents a synthesis
between traditional practices and a modern technology.
In Auroville, CSEB are stabilised with 5% cement and have an average
dry compressive crushing strength of 50 kg/cm2 (5 Mpa) and a wet
compressive crushing strength of 25 kg/cm2. The water absorption is
around 10%. Country fired bricks have resist at around 35 kg/cm² for
the dry compressive strength and have a 12% water absorption rate.
The Auroville Earth Institute has designed manual presses for CSEB

.
Building constructed using compressed earth block.
STABILISED RAMMED EARTH
In Auroville, the earth is rammed by hand. Until 1994, Auroville had only one
house made of raw rammed earth. Stabilised rammed earth was promoted
since 1995, after the construction of Mirramukhi School
(presently named Deepanam). Stabilised rammed earth presents the advantage
of being cheaper than compressed stabilised earth blocks.

Stabilized rammed earth foundations-

The soil is excavated from the trench foundation. It is sieved and then measured
at the same time on the side ofthe trench. Sand always needs to be added. In
Auroville, we use always 5 % by weight of cement and the mix is as follow: 500
litres soil + 200 litres sand = 1 bag cement (50 Kg).
Stabilized rammed earth foundations-
Stabilized rammed earth walls-
A slipping type formwork has been designed and developed. The panels are lifted up and the
walls are built like piers walls. Our process is similar to the modern rammed earth system
practiced in USA or Australia, but adapted to the local context of a developing
country. We ram by hand and we have developed also some peripheral equipment.
Some sand is always added: 25 to 30 % according to the soil quality, so as to reduce shrinkage.
Cement percentage will vary with the soil quality, but in Auroville, we always use 5 % by
weight of cement.
VALUTED STRUCTURES
This R&D seeks to increase the span of the roof, decrease its thickness, and
create new shapes. Note that all vaults and domes are built with compressed
stabilised earth blocks which are laid in “Free spanning”
mode, meaning without formwork. This was previously called the Nubian
technique, from Egypt, but the Auroville Earth Institute developed it and found
new ways to build arches and vaults.
COST EFFECTIVENESS OF EARTHEN BUILDINGS
Earthen buildings have the advantage of using local resources and being labor intensive.
Therefore, most of the time, they cost less than conventional materials and
technologies. The final cost of a building will depend mainly on the design, the type of
finishes and the project management. In all cases, the technologies implemented are
cost effective.

In Auroville, a finished m3 of CSEB masonry is always cheaper than fired bricks: 15 to 20

% cheaper than country fired bricks. Walls made of compressed stabilized earth blocks
are already cheaper than fired bricks

but stabilized rammed earth walls are even cheaper than CSEB masonry. The material
for CSEB or stabilized rammed earth is the same, but the difference comes from the fact
that the blocks have to be cured on the ground, lifted and built by masons later on.

In the case of stabilized rammed earth, the walls are made by semi skilled labor and
they stand in place at the end of the day. Therefore, a finished m3 of rammed
earth wall is 20 to 30 % cheaper than CSEB wall and 30 to 50 % cheaper than fired
bricks.
Rat-trap bond in wall construction:
There are several types of bonds developed in
different countries from time to time. They are
called as stretcher bond ,English bond, Flemish
bond and rat-trap bond. The rat-trap bond is laid
by placing the bricks on their sides having a cavity
of 4″ (100 mm), with alternate course of
stretchers and headers. The headers and
stretchers are staggerd in subsequent layers to
give more strength to the walls. The main
advantage of this bond is the economy in use of
bricks, giving a wall of one brick thickness with
fewer bricks than a solid bond. Rat-trap bond was
commonly used in England for building houses of
fewer than three stories
The main features of rat-trap bond wall are:
• Strength is equal to the standard 10″ (250 mm) brick wall, but consumes 20% less
bricks.
• The overall saving on cost of materials used for construction compared to the
traditional 10″ wall is about 26%.
The air medium created between the brick layers helps in maintaining a
good thermal comfort inside the building. This phenomenon is particularly
helpful for the tropical climate of South Asian and other countries.
• As construction is done by aligning the bricks from both sides with the
plain surface facing outwards, plastering is not necessary except in a few
places. The finished surface is appealing to the eye.
• Buildings up to two stories can easily be constructed with this technique
(Figure 2). Baker has pioneered this type of construction and had built
such houses more than 40 years ago, without showing any signs of distress
till now.
• In RCC framed structures, the filler walls can be made of rat-trap bond.
FILLER SLAB IN ROOF: This is a normal RCC slab where the bottom half
(tension) concrete portions are replaced by filler materials such as bricks, tiles,
cellular concrete blocks, etc. These filler materials are so placed as not to
compromise the structural strength, result in replacing unwanted and non-
functional tension concrete, thus resulting in economy. These are safe, sound and
provide aesthetically pleasing pattern ceilings and also need no plaster

The main features of the filler slab are:

• Consumes less concrete and steel due to reduced weight of slab by the
introduction of a less heavy, lowcost filler material like two layers of burnt clay tiles.
Slab thickness minimum 112.5 mm

• Enhances thermal comfort inside the building due to heat-resistant qualities of

filler materials and the gap between two burnt clay tiles.

• Makes saving on cost of this slab compared to the traditional slab by about 23%.

• Reduces use of concrete and saves cement and steel by about 40%.
FERRO CEMENT TECHNOLOGY
Although ferrocement is not strictly a 'sustainable' technology as it uses cement
and steel, it nevertheless employs them in a highly efficient and cost-effective
manner. Ferrocement is a thin cement mortar laid over wire mesh, which acts as
a reinforcement. It is relatively cheap, strong and durable, and the basic
technique is easily acquired. Ferrocement in Auroville is used, among other
things, in the construction of roof channels, doors, water tanks, latrines, slabs,
various form works and biogas plants
FERRO CEMENT TECHNOLOGY
•A ferrocement is a thin wall of reinforced cement, where layers of continuous
mesh are covered on both sides with mortar n
•Ferrocement elements are durable, versatile, light and waterproof n
•A ferrocement channel (FC) is a longitudinal element of a curved section
(often semi-cylindrical). It is precast using moulds
•A ferrocement channel uses less cement and steel while having the same
strength as the same RCC
•FC are used for floors or roofs, but are bad thermal insulators
•A major cost reduction is achieved compared to RCC
•A simple and cheap manufacturing set up is needed but the areas for
prefabricating and curing need to be quite large It is easy to acquire the skill
and easy to manufacture
•A constant quality control is needed during the manufacturing process and a
proper curing is needed for one month
•If the channels are not manufactured on site, transportation has to
be organized while taking care against damage
•Ferrocement channels are lifted into place and can immediately be
joined together in order to provide a shelter
•No need of scaffoldings, shuttering, concrete mixer or vibrator