Monthly Archives: October 2011
If you think Madras terrace roofs are forgotten, just visit Auroville to see a few of them standing high
If we pull out any textbook on flat roofing written during the last century, it’s possible that the most prominent chapter would be on Madras terrace roofing. Those were the days when flat roofs were becoming popular, where vernacular flat roof forms had one or the other problems. The Madras terrace method of construction, in many ways, incorporated the best of all known roof forms, avoiding their pitfalls. Thatch roofs were not fireproof, roofs with twigs and branches had termite problem, and mud floor roofs were thick and heavy.
Also, there was a desire to move from the kutchha or seemingly short life approach to pucca , long-term methods. The role played by the British engineers in the evolution of Madras terrace needs to be mentioned here.
Wooden beams, normally teak wood in those days, would be first placed upon opposite walls across the width of the room, 18 to 24 inches apart. In case room spans are wider, steel sections would be first 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 45 degrees 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 where nearly half the volume would be made up of lime mortar, three parts brick, one part gravel and one part sand. This layer provided the compressive strength and load bearing capacity to the roof. This layer needs to be well compacted, cured and levelled. The final layer would depend upon the slab being an intermediate one or the final roof. If intermediate, a floor finish like red oxide or lime mortar would be applied and if final, there would be courses of flat weather-proof tiles topped by thick mortar to slope.
In case we believe Madras terrace roofs have already been written off, we need to rethink. There have been attempts in a few cases, including at Auroville, to revive this technology.
We may not get the same old terrace tiles, but get thin perforated WPC tiles, cladding tiles and such others that can be used to build up the roof, supported by steel sections.
The roof would be thicker than our RCC slabs that should be considered in ensuring required floor heights.
Incidentally, the roof type was termed as Madras roof due to its widespread use in Tamil Nadu, though it became popular all over south India.
Even today, we occasionally meet people who can recollect having got their houses done with Madras roof.
This system with wooden cross beams does not need centering, allows faster construction and demands less structural skills.
Can the way generations before us lived for thousands of years be continued today? If some ideas are extinct today, where did they err? Do they have any future at all, or are they better forgotten? Before we go into this debate, let us look at some of the past practices, now less used and on the decline.
If we walk into any typical village, we routinely see houses where the roofs have closely placed wooden beams, often as close as six inches, which have wooden twigs and short branches above them, running in the opposite direction. There could be some dried leaves visible above them, or it could directly be a layer of mud mix. These houses were built with minimal cost, often termed as kutcha and face fire, rodents and such other problems. Alternatively the wooden cross beams could be topped with a piece of burnt flat clay tile. The tile layer gets a mud layer on top with the final floor finish.
Where ample quantity of construction timber is available, we see wooden cross beams at a wider span, say 1 to 2 ft. wide, which support a layer of min. 1.5 inch thick wood plank on top. In most houses, a thin layer of lime concrete could be seen above this, finally finished with red oxide floor. Mud flooring mix could also be used above the mud planks, in low termite prone areas. This wood beam concept comes with different variations, among the popular ones in many Sates being stone slabs replacing wood planks as the base of floor material. Any good local stone could be used for this purpose, though stone slabs have defect lines depending upon their material composition, hence are liable for cracking.
This system with wooden cross beams does not need centering, allows a faster construction and demands less of structural skills. These roofs are local by nature, hence more eco-friendly and sustainable. On the negative side, we may list the difficulties of electrification, and feasibility of base materials such as wood or cuddapah. However, this system could be revised by replacing wooden cross beams with steel joists and the sub-floor base by flat hollow clay hourdi blocks or granite or RCC slab precast at site.
When a construction idea popular for centuries loses out, mostly it happens for no mistake of the idea. People may make a mistake in implementing a construction element, but that does not mean the idea is wrong and needs to be discarded. However, if seemingly better ideas get introduced, the earlier systems become less desirable. Most traditional vernacular roofing ideas are still valid and in case newer, better ideas are not possible in the given site, can be replicated.
To that extent, it is advisable to do research on our past architecture and ready them for modern applications.
Why are seemingly unsustainable practices of today more dominating, while the eco-friendly practices of yesterday are forgotten?
Those who have commissioned a building project possess a special knowledge that the others do not. Simply stated, it is the awareness that getting a building, specially a house built, is easier said than done! More importantly, it is learning about the need to simplify every construction procedure, of course without compromising on design or quality. To this end, roof being among the more complex part of building construction, has seen more research than other component parts, with much that could be written about roofs.
Yet, nearly everywhere we see flat RCC plastered and painted roof slabs today. Quite naturally, there are reader enquiries wondering why discuss domes or vaults and who can build them after all! Every alternative idea has limitations in terms of quantity or popularity, lest it too would have been the mainstream activity. Some of the roof alternatives we are discussing are actually not mere alternatives, but time-tested ideas practised for thousands of years.
The only challenge then is to simply revive them. May be, as much as discussing the idea, we also need to discuss why these proven ideas have lost their edge, to understand why seemingly unsustainable practices of today are dominating, while the eco-friendly practices of yesterday are forgotten.
Among the major issues that we are confronting today is lowering skill levels. It is not so much because people are no more capable, but because people are not being employed for specific tasks, hence lose out on the practice so essentially required in construction industry. We the professionals then blame the construction scene saying we no more get good carpenters! If prefabricated windows replace wooden windows; if steel shuttering replaces wood plank shuttering; if ready-made kitchens replace hand-made kitchens; and then if carpenters cannot get a full month earning, who is to be blamed?
With reduced employment opportunities, the younger generations ignore specific tasks such as carpentry. In masonry category, building arches and domes are among the major casualties, but more dangerously, nowadays we keep hearing about bad brick walls because the young masons do not know how to build a wall. If these rumours become a reality someday, that will be the end of good buildings in Indian cities.
What are the implications of this impending doom? Quality assurance by factory manufacturing overrides quality by human skill perfection. Manufacturing, despite benefits including economics, speed, delivery and good finish, leads to many traps such as energy consumption, low recyclability, and unequal wealth distribution. While a certain degree of manufacturing is essential towards a basic building, construction industry mainly relying upon produced, branded, transported and site supplied chain of materials could be disastrous.
It may not lead to a sustainable future with the construction sector already adding more than one-third of greenhouse gas emissions, and specifically in Indian contexts, where we need to employ and feed millions of people. As such, all alternative and eco-friendly ideas need to be welcomed today.
Masonry vaulted roofs, despite being a common historic factor, lost their popularity primarily due to centering efforts and costs.
Different style: Alternative architecture has successfully explored curved elements in a building.
Nature is not made up of straight lines, while buildings are made up of only straight lines. Accordingly, nature can never build the Taj Mahal and we can never construct a banyan tree. Somewhere have we missed out of creator’s wisdom or are we destined to be the opposites? Is there a process difference between the two, where nature grows slowly, while humans build fast?
Growing body of literature, research and experimental buildings have told us that we cannot emulate nature fully yet, but are slowly inching closer. Of course, mainstream architecture still continues with straight constructions, but the alternative architecture has successfully explored curved elements in a building. We need the floor beneath us to be flat, hence curved slabs are not possible for intermediate floors, but a curved final roof may be considered to get the benefits of a different skyline for the building.
Masonry vaulted roofs, despite being a common historic factor, lost their popularity primarily due to centering efforts and costs. Their load bearing capacity, however, is surprisingly large, as such we see vaults covering halls as wide as 100 ft. in the Roman Empire. Being both curved like a semi-circular arch and oblong like a half-barrel or tunnel, these roof forms make the site work complex. What if we can avoid centering? Nubian vaults on moveable centering and hourdi vaults offer this choice.
Vaulted hourdi roof is comparable to Mangalore tiled roofs. Flat hollow clay hourdi tiles measuring between 3x9x16 inches and 3x10x24 inches are placed over M.S. sections, where inverted T-sections take the tiles on top. While such hourdi roofs are possible in straight slopes like Mangalore tiled roof, gently curving they give additional strength, attraction and better water proof quality. Both full-curved vaults and half-curved profiles are possible with hourdi roofs, where curve shape can be worked out to avoid trusses up to certain long spans. Surface being curved, we get wedge-shaped joints between two flat tiles, which can be easily packed with water-proof mortar mix to make them water tight. Except for this pointing of joints, rest of the top clay tile surface is left natural, looking earthy red.
A few sample pieces of hourdi tiles should be ready at site, whose dimensions should decide the precise spacing of steel members in the roof fabrication. Curving the steel T-sections need to be carefully done, all to the same curvature, otherwise the tiles may not fit properly. While laying the hourdi tiles, temporary support may be provided to the steel fabrication.
These roofs cost more than Mangalore tiled ones, but are secure, hence can be used for indoors. Incidentally, they are cheaper and much faster than RCC roofs, and can be fabricated to fit even after the walls are done. Tiles can be reused if dismantled and provide the different look that people may be seeking!
When time-tested ideas get fogged, revalidating them demands fresh efforts. Take domed roofs for instance.
A simple question: besides the flat and sloped roofs, what roof types do we commonly see in historic buildings? The answer from a majority of us would be: domes. Until about 100 years ago when steel entered the construction industry followed by RCC applications, domes and vaults (long roofs semi-circular in shape) were among the most common approaches for large buildings all over the world. Even today, in areas where only mud is available as the local material, the smallest of houses also has domed roofs.
If masonry roof structures ruled the world for thousands of years, they cannot be invalid now just because RCC is in vogue today. When time-tested ideas get fogged, re-validating them demands fresh and new efforts. This is what Hassan Fathy, an Egyptian architect did, about 70 years ago, in re-discovering the Nubian methods of making brick domes and vaults. While designers had written off masonry domes as an obsolete idea, Fathy sought masons who knew about the dying art of building them and went ahead with the projects. In India, Auroville and ASTRA group at IISc. played a pivotal role in making them once again popular.
Built in short time
Natural semi-circular domes can be built in a short time without formwork using Nubian methods. The centre pint of the dome is marked on the ground where a pipe is pivoted, which could be rotated to ensure the designed distance and radius of each course. Bricks are applied with stabilised mud mortar and placed along the radius. Since they are guided by the pivoted radius rod, as the courses rise, dome shape automatically evolves. Being a curved surface, one face will have wider joints, which can be tightly wedged. The mortar should be paste-like with high water content, such that each brick gets stuck to the other. Thinner the bricks the better, because lesser the masonry block weight, lesser the downward thrust.
RCC domes are equally well possible, but will cost more and have greater construction complications; hence the alternative modes of dome construction could be considered. Corbelling is another option to get either the vault or the dome. Here every subsequent course of brick projects out of the previous by few inches, resulting in a circular form, finally to close in on the top. The oldest surviving corbelled dome found in Greece is now over 3,500 years old!
In recent times, masonry domes have resurfaced with hundreds of buildings already built around us. They work out cheaper, appear unique and above all highlight the feasibility of the alternative ideas. Of course, domes have never been a regular part of our traditional residential architecture, though many masonry domes and vaults are found in traditional public buildings designed for a cultural image or for large gatherings. Anyway, in many parts of India, local masonry materials still being available and skilled labour possible, masonry constructions continue as a viable option.