Monthly Archives: September 2014
It is an irony to realise that the problem of modern roofing is often the problem of erecting the centering too. The more complex the roof with curves and fluid shapes, equally complex will be the temporary support.
Incidentally, even with the ordinary flat RCC roofs, the centering cost could be anywhere around 25% of the total cost of roof, excluding the finishing cost.
This happens partly because the concrete roof has to be cast by pouring the mix on a flat pre-set surface; hence the surface has to be created before hand. Traditional buildings most often had stone slabs, wooden beams, clay tiles, thatch and such individual components to be lifted up and placed, hence required part support only. Even today, by reverting to the old practice, we can save on the centering cost.
In this direction, pioneering research has been done by Jagadish, Reddy and Yogananda, civil engineers of the Indian Institute of Science, who formed a group called ASTRA. They suggested alternative roofs using masonry and found curved roofs called vaults to be strong and economical. Instead of placing a full surface centering, they suggested we can provide part support to erect the roof and keep moving this support to complete the roofing.
Once the walls of the room, preferably square or rectangular, reach the roof level, a wall beam is placed in L shape along the lower ends of the vault. This shape houses the two ends of the specially fabricated steel truss, two of them placed adjacent with just enough gaps where masonry blocks can be kept on top and the roof built using rich mortar. The two pieces are tied to avoid them falling apart. Once the blocks are placed, the formwork is moved the next day to repeat the process.
Though stabilised blocks have been popularly used in Bangalore, clay or cement blocks can also be used, as long as it is all done under supervision.
Where the upper floor has to be useable, vaults can be done fairly flat with the sides filled up to get another floor. Normally these are used for the last roof and top surface finished with joint water proofing.
This system does not immediately suit barrel vaults, but works well with segmental vaults with catenary curve. Profiling the catenary curve is important to achieve best results. The wall beams are necessary to balance the side thrusts.
In traditional buildings, thick walls or side buttressing were used to get the structural stability, which we can not afford to do today. Up to 12 ft. span, this system makes ecological and economical sense. For wider spans, thicker base and thinner top can be provided. The thickness of vault itself can be altered based on the room sizes.
Building vaults with moving supports has been around Bangalore for over 20 years now, the early models still going strong. Unfortunately, such radical ideas are not known to too many owners and builders, as such continue to be ignored.
Ask any one with experience in construction about formwork and shuttering, they are likely to say how it is time consuming, expensive and often a headache. More so in urban centres where it is difficult to get skilled people who can erect the formwork to precision. To cast a flat concrete roof, we need to create the flat surface in advance, complete with supports and capacity to take the load of the roof. If it is complicated with levels, curves, varied thicknesses, different geometries and such others, that’s then a prescription for errors.
Incidentally, our traditional buildings escaped this burden – most often they lifted the wooden beams and masonry materials one by one to assemble at roof level. Flat or sloping roof profiles made no difference to this simple technology. Of course, they would have erected temporary supports for some kind of forms like domes, but most common buildings were built without formwork.
Would it not be wonderful to build roofs without or with minimum formwork? After all, what we finally need is the final roof and not this temporary roof support. This thought led our modern engineers to discover methods that would use components made ready on floor to be lifted up. The initial ideas explored pre-cast beams to replace wood and then place smaller segments of roof elements made in site, which led to the arch panel roof which uses no formwork at all. Everything is assembled on top.
Considering they are multiple elements, ensuring a water-proof surface has been a challenge in this technique. To that end, some prior experience is required to do the arch panel roofs. What if the roofs are homogenous? We can avoid many irritants like cracking joints, water proofing the roof and such others. The scientists at Indian Institute of Science, mainly Dr. Jagadish and Dr. Reddy, focused on the traditionally popular domes and vaults, to know how to re-introduce them as a cost cutting measure.
The main inspiration came from roof forms in historical buildings, primarily revolving around domes and vaults, i.e. curved roof forms. Architect Hassan Fathy had demonstrated an ancient technique to build them without any formwork and slowly the idea percolated to India also. These ideas are generally cheaper, appear more unique and make the job much simpler. Accordingly, we see them at the Development Alternatives building in Delhi and the building centre in Auroville. Slowly many architects practising alternative design ideas took these ideas and tried spreading it.
While the pre-condition for the research was to reduce cement joints, it also led to newer architectural forms and challenges. Coupled with further alternative materials like stabilised mud block, the roofs without shuttering met the expectations of many clients.
These alternative roofs create larger volumes inside, in case of hot regions, increasing the indoor thermal comfort. Mostly they are made of natural materials, thus reducing the embodied energy of the structure as a whole, becoming green.
The Indian construction industry operates on a long delegation chain stretching from owner, manager and designer at the starting point to the helper at the other end. In between we have the builders, supervisors, sub-contractors, skilled personal, assistants, vendors, installation team and such others mostly operating on no singular set of guidelines. In such a rather complex system, maintaining inter-personal communication, reaching the right drawing to the right person in time and ensuring execution as per prescribed standards is a tough task.
Given this context, it is commendable that The Energy and Resources Institute (TERI) has been attempting to set out an agenda for green buildings through GRIHA (Green Rating for Integrated Habitat Assessment). While most of the internationally devised rating systems have been tailored to suit the building industry of the country where they were developed,
GRIHA considers many local issues, besides critical ideas such as embodied energy, minimising ozone depleting materials, adapting efficient construction technology and accepting non-air conditioned buildings. TERI states that ‘by its qualitative and quantitative assessment criteria’, it would be able to ‘rate’ a building on the degree of its ‘greenness’.
GRIHA has 34 criteria listed under varied sub-headings such as site selection and planning, building envelope design, building system design, selection of ecologically sustainable materials, integration of renewable energy, indoor environmental quality, conservation and efficient utilisation of resources, building maintenance and innovation points. There also are provisions for large developments, prequalification and such others.
TERI accepts that “It is a known fact that it costs more to design and construct a green building. However, it is also a proven fact that it costs less to operate a green building that has tremendous environmental benefits and provides a better place for the occupants to live and work in.” Given this understanding, ‘the challenge of a green building is to achieve all its benefits at an affordable cost’.
To this end, ADaRSH (Association for Development and Research of Sustainable Habitats) is joining hands with TERI and together they have launched SVAGRIHA (Small Versatile Affordable GRIHA) ratings. It is a significantly simplified, faster, easier and more affordable rating system, especially for small projects.
The present approach to identifying green buildings by TERI and IGBC are not based on proven performances, in which case the rating should be given five or ten years after they are built. Instead, during construction itself assessment begins and ratings are issued by the occupation time, largely based on an imagined future performance. Besides this lack of logic, setting of standards poses both problems and potentials.
Rating systems in general make the design and construction of buildings even more procedural than the prevailing, thereby increasing the problems. Of course, there is a huge potential also in this tool helping organise the building industry, thereby raising the standards. TERI GRIHA rating system is focused on achieving the latter.
(The author acknowledges TERI sources for the contents in this essay).
Residential units and homes are arguably the single largest category of building types in India today, going by the square foot area built. While the mega buildings in a few cities and industrial units may appear large in size, they are few and far in the larger land mass of India. If the residential sector, including individual houses, hotels, hostels, guest houses and such others could be turned green, we can equate a major counter balance to the energy guzzling urban public buildings.
Unfortunately most such buildings are small, excepting a few apartments, factories and hotels. As such, the owners tend to ignore the power hidden in their own spaces. For those who are interested, adequate information base is lacking. In this direction, IGBC and TERI are doing pioneering efforts, reaching out the ideas of eco-friendly homes.
The Green Building Movement in India has been spearheaded by IGBC since 2001 and today is known for its rating systems, though it has other activities outside rating also. In 2008 it introduced the Green Homes Rating System, which is based on accepted energy and environmental principles and strikes a balance between known established practices and emerging concepts.
The rating system is a voluntary and consensus-based programme. It is designed to be comprehensive in scope, yet simple in operation. It evaluates certain mandatory requirements and credit points using a prescriptive approach and others on a performance-based approach. The project teams interested in the certification first register with IGBC, submit supporting documents at the preliminary stage and again during the final construction stages. These reports get reviewed by third-party assessors with review comments. IGBC will consider these documents and recognise homes that achieve respective rating levels with a formal letter of certification and a mountable plaque.
The rating system addresses green features under the following six categories:
Site selection and planning
Materials and resources
Indoor environmental quality
Innovation and design process.
Each section has many sub-headings suggesting actions towards varied topics such as land topography, facilities for the workers, rainwater harvesting, efficient plumbing and electrical fixtures, generating and handling waste, local materials, recycled materials, day lighting, fresh air ventilation, cross ventilation, low VOC materials, exhausts, and innovative ideas.
Green homes, the criteria for which are listed by IGBC, can have tremendous benefits, both tangible and intangible. While tangible ones are reduction in energy and water consumption, the intangible benefits include enhanced air quality, excellent day lighting, health, well-being of the residents, safety benefits and conservation of scarce national resources.
However, it is not mandatory that every house project has to seek ratings – it is purely a choice of the owner. Yet, referring to the rating dossier gives us a checklist of options to choose from, thereby assisting every house project to adopt better practices.
P.S.: The author acknowledges IGBC sources for the contents in this essay.