Alternatives of any kind are sought after when there are choices offered and also when a special need arises which cannot be satisfied by the available conventional means. In building construction too there need to be choices of techniques and materials. Architect Chitra Vishwanath, Biome Environmental Solutions Pvt Ltd, takes a look at alternative sustainable roofing options.
To take the issue of alternatives forward let us compare the proliferation of use of Polyester fabric in place of “cotton”. Polyester got accepted because it did not need ironing, was easy to wash and also was cheap. Then the market came up with cotton and polyester mix which brought in a larger degree of comfort along with the ease and less crumples. Similarly, the kind of roofing decision largely goes by either cost or looks both being highly subjective. Surely, there is need for a larger set of parameters -objective ones – to choose from going beyond cost and looks. Thus in this article we will explore as to what those objective parameters ought to be in the scenario of resource and energy constraint without shortchanging cost and looks but formulating a set of modalities to arrive at informed decision.
Currently, in India, the construction practice largely follows use of RCC for roofing. The use of RCC has proliferated because of the ease with which it can be executed and a warped sense of it being stronger and cheap. Government categorization of RCC roofs being Pucca structures has also added to the sad demise of other forms of construction methods and materials which were prevalent from long time in India. At no point it is discussed that these roofs when not properly insulated, heat up, radiate back the heat in the night times to the interior, require heavy structure and are high in embodied energy.
Embodied energy in construction brings together the embodied energy of the materials by themselves and in combinations to make the system. Since embodied energy also takes in account transportation costs, the lower the embodied energy, the lower will be the pollution and GHG emissions. Construction materials are either quarried like stones and soil or are manufactured from the quarried materials like steel and bricks. Use of the former entails lower embodied energy than the manufactured materials.
Soil has been a building material from time immemorial but mostly for the walling purpose. As roofing its use was limited to a leveling surface over a timber and grass roof. It also was limited to being a floor and not a final roof. Bricks have been used for roofing as vaults, domes and thin bricks in Madras terracing and jack arch roofs. “Madras Terracing” is constructed with very well burnt thin bricks bonded with lime and supported on Palmyra or teak wood beams.
Gradually, stones replaced bricks and I-sections replaced wooden beams depending upon the available material, skill levels and the loads the floors/ roofs had to carry. Sadly, today the material of choice is mostly RCC whether it is in high rainfall area like Kerala of hot dry climate like Rajasthan.
Brick though a very versatile material is not very sustainable with respect to its need of burning. Brick burning leads to depleting forests as well is a large contributor to GHG emission. Cement and steel in RCC too are pollutants with large ecological footprints. This leaves a burning question as to what material should one use with a shortage of 0.2 billion homes in the country (Indian Housing Census of 2011).
When materials are transported long distances they add to pollution and costs. Indian Institute of Science Bangalore, Civil Engineering Department and Auroville Earth Institute, Puducherry have done extensive works in use of soil for construction. Soil is one of the most readily available material and best when sourced from below one’s plinth. The soil sourced from foundation or basement excavation can be turned into blocks with a minimum stabilization of 5-7%. These blocks can be used for making panels for roofing, as units for vaults and domes. These are best suited to be the most ecological choice for roofs and floors. These are also very pleasing to the eye and can be combined to create very stunning spac.
Madras Terrace Flat Roofs: Wooden beams are placed upon opposite walls across the width of the room, 18 to 24 inches apart. In case room spans are wider, steel sections are placed dividing the room into shorter spans, along which teak beams run. High density and high strength clay bricks, made to special thin size measuring 1”x3”x6”, are used in Madras terracing. Properly mixed and matured lime mortar is used for bonding the flat tiles that are placed at an angle of 45o to the wall, or diagonally across the room width. These terrace tiles, placed on the edge, ensured tensile strength. The roof is cured for a minimum of one week to achieve early setting. Thereafter, a three-inch thick layer of broken bricks or brick bats would be laid. This layer provides the compressive strength and load bearing capacity to the roof. The final layer depends upon the slab being an intermediate one or the final roof. If intermediate, a floor finish like red oxide or lime mortar is applied and if final, there will be courses of flat weather-proof tiles topped by thick mortar to slope.
Vaults and Domes: These are made with similar sized blocks as used for walls. The units vary from 100mmm to 150 mm thick and use of the various thicknesses is dependent upon the span. Both vaults and domes can be filled with light building debris like Styrofoam and mixed with clinkers to get a leveled floor above. This way the intermediate floor also takes care of the waste generated around a building.
Pre-cast Panel Roofs: Developed in Indian Institute of Science, Bangalore, it is a pre-cast system of making a roof and is newer and better version of the old system known as “Jack Arch “roof. Jack arch roofs were not precast. Precasting aids in making the construction faster and also employs women since heights need not be negotiated. There is lower use of steel and cement thereby reducing the overall embodied energy as can be seen in the table.
These are but few examples but they all contribute positively to our future in the sense that while they use less materials for construction are also treading lightly on the earth.