Today everyone is chanting the mantra of green – in environment, agriculture, architecture or products. However knowing how subjective we can be on our opinions and argue in favour of our personal ideas, how do we ensure that we all agree on what green means? Without a commonly understood and agreed upon criteria for identifying the green, say in building materials, we will not be able to converge on a larger agenda of sustainable buildings.
Many institutions have strived towards defining the characteristics of materials, mainly Bureau of Indian Standards (BIS), The Energy and Resource Institute (TERI), Indian Green Building Council (IGBC) to name a few. Considering that many experts have worked for years to arrive at the norms for assessing building materials, the standards stated by these have come to stay as yardsticks for today. In an over simplified manner, the following are the major parameters.
The value point Among the important criteria is the R value, a figure that suggests the thermal resistance of a material to conduction of heat from outside to inside through the material. Naturally, the thicker it is lesser heat gets transferred, keeping the indoors cooler by passive means. Here lies the secret of traditional buildings being cool, with massive walls and thick roof! Also, if the material is hollow inside or low density, it offers greater resistance. However, if it the material is dense and heavy, more heat gets transmitted.
The next criteria U value is directly related to the R value, a number that refers to the rate of heat transmitted in a unit area. The figure may from 0 to 1, depending upon the quantity of heat transmitted. Of course the extreme figures refer to none of heat or all of heat getting conducted may be rare, with most cases reporting in the mid range.
A related term is thermal mass – the nature of the material to act like a store house of temperature, in a way balancing the outside and inside variations in temperature. All masonry walls have good thermal mass behaviour keeping cool summers and warm winters, while transparent materials like glass are of low efficiency.
Raw material saved is an important criterion, mostly ignored at present. It could be in the manufacture of a material or its usage in construction. Nowadays many alternate options for producing cement is being discussed to make the process more effective. Reference construction, if thicker bricks are used reducing the mortar joints, there will be saving in mortar for the joints. Interlocking joints with no mortar have also proved to be possible. Like wise, how much waste the material generates either during manufacture or during construction is also a major consideration in assessing a green material. To illustrate, glass has high waste production, so reusing broken glasses is being encouraged in the production of new glass itself. There are more criteria to assess the materials that could be looked into.
