Vernacularity of Thanjavur – Traditional Architecture

Thanjavur is a traditional town that dates back to the 3^rd century AD. It is located in the South-East part of India at 10°46′ N latitude and 79°7’E longitude with an elevation of 88m MSL. It is located in almost the geographical centre of Tamil Nadu and possesses rich culture and tradition. Due to its geographical location, the vernacular architecture of this region could be considered a representative style whose influence is seen in all the vernacular traditions that prevail in other parts of Tamilnadu.

Vernacularity

Rural vernacular settlements in the Thanjavur region could be divided into two groups. One is the consciously planned settlements, which are community-based, and the other one is the organically grown settlements which are occupation-based. Vernacular houses in this region had their origin in a humble single-spaced rural hut, built by the locals with the available knowledge of materials and techniques. Later on, due to the increasing needs and requirements, and also the exposure to various applications of the material resources and technical skills, the residences have undergone various changes and transformations at different stages of development. So, the study was conducted in a selected sample at Melatur village and is analyzed to identify the solar passive techniques adopted in the design.

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Construction Details and Materials of Building Components

Walls

The external walls of the houses are completely shaded on all four sides, which is an essential pre-requisite, in warm humid climatic conditions. In a strict row housing pattern, the wall surface exposed to the atmosphere is reduced to the maximum extent, protects the structure from radiation, and avoids heat gain considerably. The walls are heavy and solid with varying thickness and construction techniques, which ensure high thermal insulation for buildings. Flat bricks, mud, and lime mortar are the predominant materials used for the construction of the foundation and walls. The variation in wall thickness makes a significant difference in the comfort performance of houses. There are a minimum number of openings in the walls, which are comparatively smaller in size and look plain and austere. The flat brick walls are plastered and smoothly finished with lime mortar, which reflects a considerable amount of incident heat.

Flat Bricks: High-density and high-strength flat bricks (8.5cm x 11cm x 4cm,) made of sediment soil, are used in the entire construction. They possess high compressive strength compared to modern country bricks and are used both in exterior and interior walls.

Mortar: The sediment soil is mixed with sand, water, and herbal juices (jaggery or molasses, nutmeg (kadukkai), and amla), and ground manually to a consistency of a nice paste, which is nothing but mud mortar which was used as the main binding mortar in the selected sample.

Lime: Kankar lime is available in plenty in this region, which is the main source of lime production. At the time of construction, jaggery or molasses,  nutmeg (kadukkai) juice, and amla juice were mixed with the fermented lime which increases the binding nature of the mortar.

Roof

A sloping roof with tile covering is the skyline of almost all the vernacular settlements in this region. The sloping roof is made of country wood (such as Enn, Poovarasu and Pillai Maruthu consist of more fibre content) or bamboo rafters and battens, covered with two to three layers of pan tiles (15cm x 10cm x 1.5cm in size, with a special locking projection at its top). As treated materials, these bamboo rafters exist without any damage for more than 250 years. The sloping roof is one of the major climate-responsive elements in the vernacular setting. It plays a significant role in reducing the incident heat on the surface, due to its angle of slope (300-350), and in reflecting the maximum amount of heat back. The roof height near the ridges is 5m, which acts as a major insulation space and facilitates good airflow inside. The eaves project 0.7m beyond the wall surface so that it protects the wall from direct sunlight. As the roof height near the courtyard is very low, it allows filtered light and dissipated heat into the spaces around.

Wherever the wooden beams come into contact with a mud wall, the wooden members were wrapped with lotus leaves and tied with threads and ropes made of fibres from the stem of the lotus flowers. This never allowed the oil content in the wood to be absorbed by the mud walls.

LATERITE BLOCKS

Laterite is a residual ferruginous rock, commonly found in tropical regions and has a close genetic association with bauxite. It is a highly weathered material, rich in secondary oxides of iron, aluminium, or both. It is either hard or capable of hardening on exposure to moisture and drying. Aluminous laterites and ferruginous laterite are quite common. Lateritic soils are formed in the tropics through weathering processes that favour the formation of iron, aluminium, manganese and titanium oxides. Laterite is found in the region with a mean annual temperature of 23 to 26- degrees C and rainfall of 1200 to 4000 mm and with a number of rainy months of 8 to 10. Laterite can occur at every altitude from sea level to about 2500 m. A considerable area of the formerly cultivated land is covered by laterite.

These soils have served for a long time as major and sub-base materials for constructing most highways and walls of residential houses in tropical and sub-tropical countries of the world. Laterite is a building material which can be used in construction from flooring to roof construction.

Laterites are formed from the leaching of parent sedimentary rocks. They belong to the Non-transported sedimentary rock category. They are formed in in-situ conditions. The mechanism of leaching involves acid dissolving the host mineral lattice, followed by hydrolysis and precipitation of insoluble oxides and sulphates of iron, aluminium and silica under the high-temperature conditions of a humid subtropical monsoon climate.

CHARACTERISTICS

The laterite of Beder, generally speaking, is a purplish or brick-red, porous rock, passing into brown perforated by numerous sinuous and tortuous tubular cavities either empty, filled, or partially filled with a greyish-white clay passing into an ochreous, reddish and yellow-brown dust. The sides of the cavities are usually ferruginous and often of deep brown or chocolate colour. The most complex varieties of the rock are the darkest coloured, and most ferruginous. The softness of this rock is such that it may be cut with a spade; hardening by exposure to the sun and air.

STRUCTURE

Laterites are greatly in structure, but can be reduced to the following three structural patterns:

1. The indurated elements form a continuous, coherent skeleton;
2. The indurated elements are free concretions or nodules in an earthy matrix;
3. The indurated elements cement pre-existing materials.

TYPES OF LATERITE

Laterite can be differentiated into two types: Aluminous Laterites and Ferruginous Laterites. The laterite in which the content of Alumina is more is known as Aluminous laterite and in which the content of iron is more is known as Ferruginous laterite. Ferruginous laterites are higher in density, are dark than aluminous and can be considered a good building material.

USE OF LATERITE AS BUILDING MATERIAL

Laterite stones have traditionally been used after direct extraction from naturally occurring laterite sources, after which they are cut into bricklike shapes for use as walling units. Laterite stone is ground and filtered using a sieve, which is then mixed with a 5% cement mixture and a chemical setting agent. This mixture is then machine compressed to form high-density interlocking bricks. They are manufactured in two widths of 6 inches and 8 inches and are also available in varying lengths. Each interlocking brick has grooves and locks on its sides which can be fitted with each other to form a block wall that does not need cement mortar for bonding. They have lower embodied energy due to the use of natural locally available materials- stone and wood. The only energy spent is on the transportation of materials. The high recyclability factor – especially in the case of interlocking blocks which don’t use connecting mortar is a bonus.

ANALYSIS

• The use of laterite is cost-effective as compared to concrete blocks.
• Reduces the cost of plastering and painting.
• Reduces heat within the house.
• Soft when quarried hardens on exposure.
• Requires skilled workmanship.
• The porosity of laterite stones is more than bricks. Thus the load-bearing structure of laterite masonry cannot be more than double storey.
• The darker the laterite, the harder, heavier and more resistant to moisture.

NATURAL HYDRAULIC LIME

Hydraulic limes are traditional construction materials and were the primary hydraulic binders used in mortars prior to the development of ordinary Portland cement (OPC) in 1824. The term ‘hydraulic’ describes a material that will set and harden under water. The process by which limes set is due to chemical hydration(reaction to form strength-developing compounds), with additional strength being gained by the carbonation (absorbing atmospheric CO2) of the free calcium hydroxide present.

In the last 100 years, the terminology that describes lime products used in building and restoration has become confusing. Hydraulic limes as defined in BS EN 459-1:2001 the current British Standard Building lime – Part 1: Definitions, specifications and conformity criteria, fall into two types, ‘Natural Hydraulic Limes’ and ‘Hydraulic Limes’. This factsheet covers the production of Natural Hydraulic Limes. Natural Hydraulic Lime (NHL) is produced from a naturally-occurring raw material rather than by blending Calcium Lime (CL) with a pozzolanic material as used in the pro- duction of Hydraulic Limes (HL). Pozzolanic materials (or pozzolans) consist mainly of reactive silica (SiO2) and alumina (Al2O3). When finely ground and mixed with lime, and in the presence of water, they react with the dissolved calcium hydroxide [(Ca)OHl2] derived from the lime to form strength-giving calcium silicate and calcium aluminate compounds.

Definitions

The use of lime and lime mortars, being traditional construction materials since Roman times, has over the years resulted in a diverse and sometimes confusing vocabulary. To assist with the understanding of this document, the following terms and definitions are used:

Natural Hydraulic Limes are used as an alternative to cement-based binders in mortars and renders, either in new buildings or in the repair and maintenance of historic buildings. NHL mortars combine some of the benefits of a cement-based mortar (setting time and strength development) with those of hydrated lime mortars.

Both NHL and HL are now classified on the development of strength attained at 28 days, in the same way as cement-based materials. There are a number of reasons why the demand for NHL-based mortars has increased recently:

Environmental Issues

NHL is seen as a more environmentally-friendly hydraulic binder. This is because the energy required to produce this material is significantly less than that for OPC and other cement. This is because the raw materials are calcined at much lower temperatures.

Technical Issues

NH Ls allow the masonry to ‘breathe’ by permitting the free movement of water vapour through the mortar, as well as the masonry unit. They attain strengths, that, though weaker than cement-based mortars, are acceptable for modern construction methods.

Structural Issues

The weaker nature of the mortars made from NH Ls allows for the accommodation of minor settlements and avoids the formation of mortar cracking. Any cracks formed tend to seal themselves by the process of autogenous healing where cracks are sealed by the deposition of calcium hydroxide, which then subsequently carbonates. Some architects prefer NHL and HL mortars, which preclude the need for expansion joints in long runs of brickwork. Irreversible moisture expansion of bricks set in OPC mortar results in a detachment of the brick and mortar (due to the strong/ brittle nature of OPC mortars). HL and NHL mortars are weak enough to plastically deform and allow for minor movement, and thus avoid the need for expansion joints every 15 m of brickwork.

Heritage Issues

For the last 10-15 years, most heritage repair work has been based on the use of either hydrated lime or NHL-based mortars. This sector tends to avoid the use of incompatible, strong OPC-based mortars. Work by conservation bodies has shown the benefits of this approach, and currently, the majority of this type of work will only specify NHL (rather than HL) if a hydraulic lime is required. NHL is considerably more expensive than cement, because of small-scale production, and currently supplies only a small specialist market. However, the Building Limes Forum consider that there will be an increase in demand for all types of NHL in the future.

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