cobwall_13mar15

Building with earth, Building the earth

Towards a safe and sustainable future

People in Centre Consulting, Ahmedabad

Why People are Abandoning Traditional Building Practices?

- Classified as a ‘Kutcha’ and gets lesser compensation as compared to a ‘pukka’ house - Government schemes like Indira Awaas Yojana and other schemes do not encourage these traditional building practices. - Status of a ‘pukka’ house is preferred encouraging owners to build with brick and RC slab, despite their poor construction quality, poor climatic performance and high cost. - Lack of practice results into loss of knowledge about the soil and technique leading to poor construction quality. - very few practicing mud artisans left.


Why People are Abandoning Traditional Building Practices?

• Weathering effects require frequent maintenance. Labour intensive and time consuming, hence not preferred.

• Salinity is a major issue causing erosion especially at the base, leading to structural damage.

• Harder to find good quality soil for construction. • Wood for construction is not easily available and is expensive.


• Truly environment friendly options, using local materials • Easily available and accessible material • Low cost option as compared to brick and RC

• Excellent thermal properties to ensure comfortable living conditions. • Less energy and water intensive and has low carbon footprint. • Can be constructed/repaired/maintained within the local socio-economic

system, does not depend on external and inaccessible system. • Greater control of the house owner in material procurement, design,

construction and cost management.

Why it still makes sense to use the Earth Based Technologies?


• Some of the constraints already addressed by good traditional practices

• Others can be resolved through further research or learning from other building practices.

Rationale


• Three Predominant Technologies Using Earth in Gujarat:

• Cob Walls: Banaskatha district, Coastal Bhal in Bhavnagar, Ahmedabad and Anand district, Kutch

• Adobe Block Walls: Kutch, Bhal (not in practice much)

• Wattle & Daub Walls: South Gujarat regions including Narmada, Bharuch, Valsad and Vadodara district, Kutch.

People in Centre is currently engaged with CRD to identify appropriate technical options for rural construction in different parts of Gujarat

Earth Based Technologies in Gujarat

Map showing Areas Visited for Case Studies in Gujarat


Cob Wall Houses

• Cob walls are constructed in layers with lumps of mud prepared by mixing water with earh and pugging the mix.

• Traditionally constructed by artisans from Oad community, who traveled from village to village to build cob walls.


Cob Wall Houses Types of Houses found in the studied regions: • rectangular house with sloping tiled roof • circular house with conical thatched roof.

There are further variations to the typology including two-three story houses, combination of circular and rectangle plan etc.


Cob Wall Houses

• A rectangular plan house with a sloping tiled roof

• A semi-open veranda and a series of parallel rectangular covered spaces/rooms. Mangalore or country tiled sloping roof with wooden under-structure

• A single or double semi-open front veranda and a back veranda in some cases.

• Otlas/raised plinths in front as well as on sides where possible.

• Occasionally, a separate cattle shed located within the same compound.


Cob Wall Houses

Protection against Rain


Combination of circular and rectangular elements

Examples of various cob wall houses

Cob wall House with a grain storage

Cob Wall Houses

Protection against Rain


Cob Wall Houses

• Longest cob wall span found 20 ft

• Cob wall thickness range 1 ft – 2.2 ft

• Tallest cob wall found (in two floor house) 14 ft

• Average Gable height (Highest point) 4.5 mts

• Roof under-structure: simple truss support or ridge beam, purlins and rafters system

• Internal floor: Out of bamboo and mud supported on wooden beams supported by the cob wall


Various protection mechanisms including grass mats, double verandah and plinths to protect the walls

Cob Wall Houses

• Circular plan house with conical thatched roof with wooden under-structure. • Circular units can function as a house in itself but sometimes function as units

of a larger household.


Cob Wall Houses

• A well integrated system of wooden members with the cob wall provides enough stability to the structure, if well constructed.

• In case of structural failures (including due to natural disasters), cob walls do not collapse instantly but rather disintegrate resulting in low impact collapse, which is less life-threatening.

• Require protection from exposure to rain/water.


Cob Wall Construction, Pandad Village • In order to understand the traditional cob wall construction process, an

extension of the existing house at Pandad village in Anand district was built by Lakhabhai Oad and his family.

• Three walls were constructed to add one more room to the existing house which consists of a room and a verandah.


Cob Wall Construction, Pandad Village

•Six steps of construction process: •Soil Selection

•Water Procuring

•Preparation of the Foundation and Base Layer of the Wall •Preparation of Soil Mix for Construction

•Preparation and Handling of Lumps for Construction

•Construction of the Wall •Soil Selection:

•Needs to be free from salinity (In areas facing salinity issues, soil is procured after rain from village ponds) •Sand content in soil should be around 40-50% (Depends on site conditions and exposure to flow of water etc. – more than required clay will result in large shrinkage cracks in the wall, more than required sand will result in washing away of the walls exposed to water)

•Water Procurement •Water for construction also needs to be free from salinity. Saline water and/or soil will result in erosion of the walls, thus needs to be avoided



Preparation of Foundation and Base Layer of the Wall: • Traditionally unstabilised cob foundations are found

• 2-3 ft deep and 2 ft wide foundation is dug and then the soil excavated from the foundation itself is mixed with water and poured back in the foundation and compacted

• A first layer of 6 inches is constructed on top of the foundation which demarcates where the wall should be constructed.

• This layer is not plinth band and the plinth may go higher than this first layer. The plinth hight depends on the usual water level during the monsoon.


Cob Wall Construction, Pandad Village Preparation of Soil Mix for Construction:

• Mud is mixed and prepared on a levelled earth surface. Preparing and mixing on the earth surface makes it easier to manipulate the water content.

• Water is added in batches during the mixing process and soil is mixed with shovel. Approximate soil to water volume proportion for mixing is 3:1, however this slightly varies based on different soil types.

• After initial mixing, pugging by feet (approx. 20 minutes) and buffalo (approx. 20 minutes) continues until there are no dry lumps of earth remaining and the mix gains desired consistency.

Cob Wall Construction, Pandad Village Preparation and Handling of Lumps for Construction:

• Small part of prepared mud is lightly pressed with foot and compacted and then separated with the help of a shovel. It is then lifted and carried to the builder.

• In the beginning, the size of the lumps is roughly 1 ft.*0.75 ft.*0.5 ft. As the height of the wall increases and the required wall thickness reduces due to the tapering of the wall. With this, the size of the mud lumps also reduces.


Cob Wall Construction, Pandad Village Construction of the Wall:

• Wall constructed in layers roughly of 1.5 ft high at a time by moulding the the mud by hand ensuring compaction

• Each layer dried for roughly about a week before the next layer is constructed. The drying period ensures that all the shrinking takes place before the next layer is constructed.

• Each layer is slightly rounded from the top, so the next layer fits on the curve of the previous layer providing better stability.

• Connection between existing and new wall or two parts of a layer can be done by inserting piece of wood in the wall. This creates a bond and ensures that the new and the old parts of walls do not separate.. Woods used for the connector piece need to resist rotting or impact by white ants.


• Identifying and understanding material properties in a cob wall construction • Structural analysis of traditional cob construction particularly its behaviour

under seismic stresses • Analysis of proposed design options developed by People in Centre • Recommendations for improving the details and the systems • Shake table test of cob wall construction – traditional as well as improvised

(if required)

Taking the Cob Construction Practice Forward


Proposed Design Options for Improving Seismic Resistance of Cob Construction


cobwall_13mar15

Documents

centre consulting

gujarat people

rationale people

traditional building

sustainable future people

rectangular house

poor construction quality

good traditional practices