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Any building necessarily consists of
components like foundation is required; the cost of the
foundation will be 20-25% of the total cost. If it is
residential the proportion will be 8-12%.
In general, for a residential building of 700
Sq. ft. floor area, with conventional construction
techniques, walling and roofing would account for half of
the total expenditure of the entire building, So, it is
obvious that, in order to reduce the cost of a building and
to have a Cost Effective Shelter, efforts should begin with
examining alternatives for walling and roofing.
We can also bring down the cost by proper
planning and scheduling of construction activities, but the
conventional techniques prevalent for walling and roofing
suffer from the following inherent drawbacks:
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They are not cost effective
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They are not easily affordable by major
population of rural India. |
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They use materials which have limited
access. |
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They use large quantities of materials
with a high energy during their manufacture. |
Techniques
for Wall Construction
There are many prevalent systems of walling.
In practice these vary from place to place depending upon a
number of factors like raw materials availability. There
widely adopted conventional forms of walling are fired brick
masonry in cement mortar and stone masonry in cement mortar.
Now let us look into the alternatives for
walling.
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Random rubble masonry in mud mortar
with cement pointing
This reduces the consumption of recent, as it is
limited to surface pointing only; where as most of the
mortar for the masonry uses mud. |
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Fired brickwork in cement mortar with
rat trap bond |
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This bond is executed by using the
brick on edge. It allows a cavity between the outer
and inner face with every alternate brick binding the
two faces. It enables savings in brick and mortar to
the extent of 30%. |
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Adobe block masonry
In this system in-situ soil is mixed with water and
hand moulded blocks are made on wooden formwork (Adobe
blocks). The blocks after being sun dried, are used
in masonry. |
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Rammed Earth Walling
In case, the soil is mixed with water into semisolid
form, and poured in between form works for walling and
rammed. |
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Compressed Earth block masonry
Compressed earth block are made by compacting the soil
mix at optimum moisture content in block press. The
“BALRAM” is one example of a manual block press. This
walling system uses compressed earth blocks and mud
mortar. Sometimes, small quantities of lime, cement
or other binder are missed with soil to improve the
performance of compressed earth blacks during exposure
to atmosphere. |
Techniques
for Roof Construction
A Variety of Roofing systems are in vogue.
But the most commonly used systems are reinforced cement
concrete roofing, asbestos sheet roofing and galvanised iron
sheet roofing.
Some of the cost effective options for
roofing include:
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Jack arch roofing using
stabilised compressed earth blocks in stabilised mud
mortar.
This is basically a flat roofing
system, formed of shallow segmented arches built over
pre-cast R.C. beams or rolled steel sections. This
system uses reusable sliding formwork which not only
facilitates speedy construction but also reduces cost. |
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Sandstone slab
This system is suitable for short spans of up to 8
feet. This is also a flat roofing system with panels
of sand stone slabs, paced on built over Tee
sections. This enables speedy construction and
involves almost no curing unlike Reinforced Cement
Concrete roofing. |
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Micro Concrete tile Roofing (MCR) this
is a pitched roofing system developed by Development
Alternatives. Micro concrete product made by vibrating
cement, sand, aggregate and a measured quantity of
water in specific proportions in an electrically or
manually operated table vibrator. There tiles can be
manufactured locally by village based micro
enterprises. This pitched roofing system can be
combined with low grade under-structure like ballies
and wooden poles. |
|
Component |
Techniques |
Rate /
Unit (Rs.) |
Water
Resistance |
Level
of skill required |
|
Walling |
Fired
brickwork in cement mortar 1:6 (M3) |
946 |
High |
Medium |
|
Fired
brickwork in cement mortar 1:6, in rat trap bond
(M3) |
712 |
High |
High |
|
Unstabilised CEB Masonary (M3) |
387 |
Low |
Low |
|
Stabilised
(4%) cement CEB Masonary (M3) |
590 |
Medium |
Medium |
|
Flat
Roofing |
Reinforced
cement concrete roofing (M3) |
337 |
High |
Medium |
|
Jack Arch
roofing (M3) |
200 |
Medium |
High |
|
Pitched |
Asbestos
(ACC) roofing (M3) |
200 |
High |
Low |
|
Micro-Concrete Roofing tile (M3) |
140 |
Medium |
Medium |
Form the above table, it is obvious that by
adopting cost effective combinations like compressed earth
blocks for walling and Jack arch roofing and micro concrete
roofing, one can substantially bring down the total cost of
a building. These have special relevance to rural housing
because all these techniques are labour intensive and not
only use local material, but also help promote micro
enterprises.
The author
is a Civil Engeener
working
with the Shelter Grouop,
Technology
Systems Branch
Development Alternatives
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