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Expert Speaks

The BEEP Team engages Prof. Claude Alain Roulet in a conversation on ‘insulation’

Claude Alain Roulet is a building physicist with almost 50 years of experience in the building sector, dealing essentially with building materials and energy in buildings. He has been a researcher and Professor at the Institute of Technology in Lausanne since 1974, and has worked not only on thermall insulation materials, but also on ventilation systems and indoor environmental air quality. Prof. Roulet assisted the Swiss Federal Government in enforcing testing and quality assurance mechanisms for building materials, particularly thermal insulation materials. In the 1980s, he took part in the national training programme on energy-efficient building design for architects and engineers. He has published several books and manuals on energy-efficient building design. Today, Prof. Roulet is an active player in the development of norms and standards for sustainable buildings.

Why is insulation needed in buildings?

Thermal insulation reduces the heat flow through the building envelope. This has two main effects.
Gives thermal comfort indoors: Thermal insulation helps in keeping a comfortable temperature inside despite strong temperature variations outside and solar radiation falling on the roof and exposed walls. It also improves comfort by reducing the unpleasant effects of cold or warm surfaces. 
Reduces the quantum of energy needed for heating or cooling the living spaces inside: Depending on the weather, the effect may be very important. In harsh climates, reduction in yearly energy use by a factor of four or more can be obtained. In mild climates, together with passive heating or cooling strategies, it may even avoid the need of a heating or cooling system.
Note that thermal insulation is not just limited to opaque elements, but also windows and doors.

What are the common insulation materials available and their suitability for application?

Temperature is physically the degree of agitation of atoms and molecules. The heat flows from hot to cold areas using three main ways: by conduction, where agitated molecules transmitting their movement by direct contact to others; convection, where heat is transported by moving hot matter; and radiation, where agitated molecules emit electromagnetic ra­diation (infrared light, or visible when very hot) that heat the matter receiving it. An insulating material should hinder these three ways, and hence have no matter (or be very light) to hinder conduction, avoid air movement, and be opaque to radiation. Indeed, thermal insulating ma­terials are mainly made of air, immobilised in a fibre network or in small bubbles, the fibre or bubble walls being opaque to radiation. Most common thermal insulation materials are mineral fibres (glass or rock wool) and plastic foams (e.g. expanded or extruded polystyrene and polyure­thane). Other materials such as organic fibres (cellu­lose, wool, hemp, hay, etc.) or foams (cork), glass foam, expanded clay or aerated concrete are also used. The main reason for this variety is that no material is suit­able for all applications but there are materials that are suitable for each application. A material that is good for one application may have a poor behaviour in others. The answer is then: there are no best mate­rials, but there are best choices for each application.

What are the different ways of installing thermal insulation?

Thermal insulation should be installed in every en­velope element: roof, walls, and even ground in cold climates. As most insulating materials cannot resist weather and stand to loads, they should be protected by an appropriate material layer. Within the envelope element, the thermal insulating layer could be basically put on the outside or inside of the loaded structure. The easiest way is to add thermal insulation from inside when the building fabric is built, and to protect this material with a thin wall. This has however several disadvantages: Thermal insulation does not go through decks and partition walls, and thermal bridges remain, which may lead not only to energy losses but also to mould growth hazards. The thermal inertia inside the building is reduced. The external building fabric remains exposed to outdoor temperature variations and resulting damages. Therefore, it is recommended to place the ther­mal insulation outside the building structure, and to protect it by an appropriate layer or additional wall. This avoids most thermal bridges, keeps the build­ing structure at a nearly constant temperature and increases the internal thermal mass of the building, thus naturally stabilising its temperature.

What are your views on use of insulation in India?

India is now strongly increasing its building stock, and new or renovated buildings will last for long. They will see the energy evolution (or revolution) from fossil to renewable sources. A sustainable building cannot spill energy, and thermal insulation is one of the most efficient ways to reduce energy spills in buildings. In my opinion, every new or retrofitted building should have a well insulated envelope, and this idea should become common. In Switzerland, before the first oil crisis, the habit was to install 2–4 cm internal thermal insulation, just to ensure thermal comfort during the cold season. During the eighties, with the people slowly becom­ing aware of energy problems, architects asked me: ‘how thick should be a thermal insulation layer?’, and I answered: ‘as thick as you can, but no less than 10 cm’. They immediately replied ‘but this is technically impossible!’. Now, 30 years later, the common habit is to install 20 cm, and everybody agrees that this is a minimum. The optimal thermal insulation depends on climate, and varies from one place to the other in India. The im­portant thing, for the future of India, is that this opti­mum should become of common use.

What are the latest trends in building insulation in Switzerland / Europe?

I would first state that the Swiss climate is closer to that of Kashmir than that of Uttar Pradesh. The Swiss rules now limit the energy need for heating in buildings, and submit cooling to specific authorisation. There is no strict rule on building insulation thickness or U-value, but a strong thermal insulation (about 15 cm of typical insulating material) is needed to comply to today’s comfort and energy requirements. New residential buildings that fulfil today the en­ergy requirements would still need about 150 kWh/ m² gross floor area of primary energy annually for all the needs. The general trend, however, is to reduce the energy use, aiming to the 2000 W society,1 while closing our nuclear power plants within the next 20 years. Therefore, the latest trends are similar to those of the European community, i.e., the new buildings aim a zero non-renewable annual energy balance.

Conducting Integrated Design Charrettes

Andreas studied at Federal Institute of Technology of Zurich in 1979. He has over 30 years of architectural and teaching experience in Switzerland, USA and Canada. He is a partner and Senior Vice President at Nüesch Development and manager of its Zurich and Lucerne offices. His recent work includes the planning and development of EbiSquare, the lifestyle mall to be built in Lucerne, Switzerland.

You’ve been part of charrettes in India and elsewhere. What has been your experience of these charrettes? Are there different challenges in India and elsewhere?

Charrettes always come with a big adrenalin boost. The clients have high expectations and all participants are under pressure for success. The challenge is to find the trigger points in the project where a substantial improvement (i.e., energy savings) can be achieved with minimal effort. That is true in India as elsewhere. But in India, the clients tend to expect energy savings with very short pay-back periods rather than calculating life-cycle costs.

What role does the architect play in these charrettes? Any special skills required?

The architect is the generalist. He does not have the specialized skills of a mechanical engineer or a green energy specialist. But he can bring these special skills to fruition by combining the knowledge of active and passive measures to multiply their effect for the client. And he must be a good communicator who can translate specialists’ lingo into the client’s language to be understood – and hopefully accepted and implemented.

What are the architectural design issues that are important to make a building energy efficient?

All architecture is local. Macro factors such as climate, latitude, local building methods, and culture must be taken into consideration. The micro factors such as orientation of the structure, building mass versus envelope, insulation versus cross ventilation, openings and shading devices are also key to energy efficiency.

For commercial buildings often the mechanical systems are emphasised for energy efficiency,which leads to the misconception that glass boxes are okay. Why is the architectural design equally important and how can we promote this?

Efficient mechanical systems are very important when attempting to reduce the energy consumption of a building. They can correct the ‘design mistakes’ to a certain degree, which will help conserve energy.However, these systems still require energy to function in the daily life of a building! Much more efficient therefore would be a smart architectural design that avoids entirely or at least greatly reduces the need for such mechanical systems. We must promote energy efficient design and weigh its potential extra costs against the reduced installation costs of mechanical equipment and the minimised energy consumption during the life cycle of the building.

From your experience as an architect as well as a developer, how is the integrated design process advantageous?

When a client signs up for an integrated design process, he already has made the most important step: He has enabled all specialists involved in the development of his building to talk to each other, learn about each other’s needs, hopes, and limitations and to start acting as a team rather than as uncoordinated separate entities. The advantages of integrated design process lay not only in a better product but also in an accelerated learning curve of all parties involved.

What are your suggestions to improve the charrette process?

In the past, we used to be satisfied if we were able to show the client a variety of methods for energy reduction. Now we begin to include approximated cost implications as well. By doing so, the client is not only made aware of the life-cycle costs of the proposed energy reduction measures but will be eased into a position where he can choose from different alternatives. He will also start to understand the importance of offering a high comfort level within the building. Higher comfort for the tenants will result in more efficiency and a greater output. I suggest looking at the broader spectrum of factors impacting energy efficiency – for the benefit of the client and the inhabitants of the building.

Prof. Ashok B Lall on Shading

Prof. Lall is an eminent architect and principal of Ashok B Lall Architects in Delhi. The firm has executed several well-known projects in India, including the headquarters of Development Alternatives in New Delhi. Prof. Lall is a strong advocate of low energy sustainable architecture. He is also engaged in architectural education and is a visiting professor at Guru Gobind Singh Indraprastha University, New Delhi.

Why is shading required in buildings?

When the weather is hot outside you want it to be cooler inside your home. If sunlight happens to enter your house, all its heat gets absorbed by the structure of the building, trapping the heat and making the house uncomfortable.That’s the reason why, through the ages in all parts of the world, people living in warm and hot climates protect themselves from the sun – like carrying an umbrella. It’s as common sense as that. Shading is absolutely essential in hot and warm climates.

What are your views on the current use of shading practices in India?

People are forgetting to shade the openings of buildings or even create shaded spaces outside the building. This is entirely the fault of the current culture of architectural design. The building is seen as an object, which is to be composed, etc. and not something that is designed in response to the climate or how the sun moves around it. This is just forgotten. This gets worse when some people start saying that to have an external shade on an opening is inviting trouble because pigeons will sit on projections and that it’s difficult to maintain. Well, I would say this is a design problem. Whatever you design ought to be maintainable and take care of problems such as birds, etc. Nevertheless you must have shading. If you retreat from the design problem, it does not mean that you have solved it. And if you fall back on the promises of the glass industry saying that you don’t have to do any shading and only darkening the glass can solve the problem, then let me tell you then the glass man is totally misinforming you.The darkened glass is picking up heat and converting the glass into a high temperature surface. It cuts down the light but not the heat transmission. And if you then ask him ‘Look we want to stop the heat transmission, so what’s to be done’, then he tells that ‘We will do a double glazing, put a low-e coating on the inside and the glass used is spectrally selective so that only the visible light comes in and the rest of the light is reflected. But it will cost you three times as much, but then that is the latest technology after all.’ As we can’t afford the latest technology, we settle for the worst of it because we want to look modern. So this is where the problem lies. I’m afraid that people have forgotten how to shade the building and they are trying to convince themselves that they are alright. This is drastically wrong.

Does the shading differ for different typology of buildings?

That’s a very good question. If you look at the problem of ‘designing a shading system’ a little more scientifically, it’s got to do with how you do get the daylight that you want, without getting the sun directly. Or, when you are getting excessive diffused lighting/radiation from outside, how you can filter it. So there is a contradiction here: you want the light to come in but you want it spread nicely in your space. And at the same time you don’t want to let in any more light than what is necessary, and also not let in any heat. Now it depends on what you are lighting up. If it is your home, then the illumination inside your home in all the rooms is not a critical requirement. If you need to do some work by the daylight, you can go closer to the window. But in an office space or an industrial space, where every part needs to have good light so that you can occupy any part of it and work there in good light, it becomes different. So depending on the type of building, how you let the light in and how you shade from excess light is a different design problem. So for residential buildings, it will be one type of solution; for commercial buildings, it will tend to be a different type of solution; and for industrial buildings, yet an another kind of solution. That’s one aspect of the differentiation for the typology of building. There is another important thing. The sun moves on a particular trajectory across the sky depending on where you are located on the globe and it shifts its trajectory during different times and seasons of the year. Hence the shading has to respond to where the sun primarily travels along. It also has to respond to the sky/horizon, especially in the hot-humid climate when the horizon is extremely bright and you get a lot of radiation. What it means is that you have to design the shade for the way your building is oriented. As the sun moves or as its intensity changes, depending on the seasons or the time of day, you end up responding to it with something variable. A kind of universal solution is a variable or movable shading system that is outside the opening or window. If you can design that then you can take care of any orientation, any time of the day, at any location

What are the different kinds of shading that can be installed in buildings? According to you, what is a better option, static shading or movable shading?

From the point of view of being able to respond to the variations in the sky and position of the sun outside or the variation in how the radiation reaches the window – that is, whether one is in a dense urban environment or out in the open – something that is movable is the right option. But, generally, something that is movable will be a more complicated device as it has to be adjusted, whether manually or automatically, and will tend to be a bit more expensive. And when you make something movable, it is more difficult to make it robust.So my general recommendation is to see what you can achieve with a fixed shading first and then add the variable component as required. So you might get a happy balance between the two things. Theoretically, a movable/adjustable device is the universal solution. But, practically, a combination may be better because of cost, durability, maintenance, and many other issues.. For example, if you have a chajja on a west-facing window, it will protect you till about 2.00–2:30 in the afternoon. And when the sun goes down and if you don’t have a building or tree opposite, the heat will start coming in. So may be you can hang a chik under the chajja and tie it down after 2.00 p.m. This chik will be cheap and will last you 3–4 years, after which you can change it. So here is a low-cost response to the idea of a combination of fixed shading – to do quite a bit of the work – and variable shading to shade the remaining part. So the options that are available are very broad. It depends on the ingenuity of the people designing.

What options does the Indian market offer for shading solutions? Or is the Indian market prepared to offer adequate shading solutions?

Are there external shading products in the market? NO, there are none. The only kind of products that are available today is a perforated or cut screen in various materials. These are fixed and they are light filtering screens. These are available. But external movable/variable shading systems that are clever in the sense that they modulate light and bring it in the way that you want and also cut out the sun the way you want are not available.

What should be done to make the market more friendly for buyers to buy such shading systems?

It’s the chicken and egg story. I live in a house and I am troubled by the heat and the sun so I draw the curtains and still the air conditioner does not work properly. Nobody has come to tell me that ‘I can do something else for you. I can put a shade on the outside, which you can adjust from time to time and suddenly the air conditioning works better.’ There hasn’t been any demonstration of external shading systems as to how they improve the condition of a poorly oriented or designed building. The first thing that needs to be done is to develop a retrofit model for existing residential buildings. It needs to be something that can be installed on your 4–5 storey building while standing inside the house. It should be robust and reasonably economical. If somebody comes up with that product and people see its benefit, it will catch on just like the plastic bucket. It’s just a question of the development of a product, its demonstration, and then its marketing. It’s bound to happen. Once that happens, the principle of external shading will be understood by the consumer. And once the principle gets understood by the consumer, then the consumer begins to demand. That’s the next thing to happen. At the moment, we tell ourselves that we need to draw curtains if there is excessive sunshine coming inside the building and that’s all we think needs to be done. We haven’t understood that heat comes in nevertheless. So the principle of external shading needs to be communicated clearly, through some popular means – whether by using a popular actor or other means. Once that is understood, and you have this alternative product on the shelf, then the market will simply pick up. That’s for the residential sector. In Australia, I saw sliding screens on the rails of balconies in a block of flats. It is common place there and people use them conveniently. It’s become the expected norm. In Greece, 8–10 storey residential buildings have balconies surrounding the rooms and every balcony has an awning. People bring down the awning during day-time and lift it at night. This is standard as people know that external shading works. Here we have not understood that.

Can you give examples of how you have incorporated shading in your buildings?

We have incorporated shading in nearly all of our projects and we have tried different strategies. The first strategy we tried was to have a window that has two layers of glass, where the inner side of the glass opens inside and the outer side of the glass opens outside and between the two glass layers we have put venetian blinds. So what it did was it became an insulating window with a break for the sun falling directly and reflecting much light and heat outside. This was a pragmatic solution of a sandwiched venetian blindbetween two sheets of a glazed window. This is in the Transport Corporation of India Ltd (TCI) headquarters in Gurgaon. It works very well but the owners have to be reminded to adjust it seasonally to get its benefit. This is for an office building. For residential buildings, typically what we are now doing is to give a fixed shading device outside the window and then building a frame attached to that fixed shade where you can attach a movable/adjustable shade like a venetian blind, roll-up chik, louvers, etc. Basically giving the user the option to attach it later. May be this way there will be different types of such options that will become available in the market, once people start seeing that it can be done. For other office and institutional buildings, we have usually used fixed shading systems and not used movable shading. Here the principle that we have followed is that the shading system should be very light-weight, should be minimally attached to the building, and it should be perforated. Its geometry should be such that it intercepts the sun during certain seasons and certain times of the day, but as it picks up the heat it loses it to the surrounding air quickly and doesn’t transfer it to the building structure. That is the heat transfer building science behind designing a shading system: the shading system will pick up the sun’s heat. You don’t want that heat to be transmitted into the building, you want to lose that heat quickly to the outside. That imposes a technical discipline. In the last project that we did, we have a combination of a fixed shading and a movable screen, which has to be moved only twice a year. When we want a bit more of the sun to come in, like in the winter months, we turn it one way. And in the summer months, we turn it the other way and cut out the late afternoon and early morning sun. So part of it is movable and it has to be adjusted manually; it has to be adjusted 3–4 times a year.

Dr. Sameer Maithel, an expert in the area of sustainable buildings and building materials.

Masonry construction using bricks is the dominant form of construction for both rural and urban housing in India. Given that India has plans to provide housing to all by 2022, a large increase in demand for bricks for housing construction is foreseen in near future. What are the energy and environment impact of bricks ? How does the bricks currently in use fare on resource efficiency parameters? and what can be done to improve their resource efficiency?

What are the different types of bricks used in India ?

Solid burnt clay bricks are the dominant types of bricks. As per the Indian census 2011, burnt clay bricks were the predominant material for wall construction in almost 65% of the existing urban households. During the period 1991 to 2011, the number of households that live in houses made from burnt clay bricks doubled (an addition of 5.5 crore new households). In addition to solid burnt clay bricks, solid and hollow concrete blocks, solid fly ash bricks, Autoclaved Aerated Concrete Blocks are some of the other types of bricks/blocks which are popular in housing construction.

What are the key energy and environmental concerns related with bricks?

Almost 1 billion tonnes of primary raw material in the form of brick earth, sand, stone aggregates, etc. are used for the manufacturing of different types of bricks and blocks. Most of the mining of raw materials for brick production is unorganized and unplanned, whether it is extraction of top-soil from the agriculture fields or mining of river sand from river beds. This results in the degradation of land and rivers. The other key concern is the large amount of fuel (coal or biomass), estimated to be more than 30 million tonnes/year, that is used for the manufacturing of burnt clay bricks. Burning of this large amount of fuel results in CO2 emissions (in the excess of 60 million tonnes/ year) as well as emissions of suspended particulate matter and other air pollutants due to inefficient combustion. Fugitive dust emissions during handling and processing of raw materials (e.g. fly ash, clay, etc) as well as from the unpaved surfaces of the brick manufacturing facilities is also an area of concern. As the brick production is likely to double from the current production level of around 250-300 billion bricks/year by the year 2030, there is an immediate need to move to resource efficient bricks.

What is meant by resource efficient bricks?

Resource efficiency is defined as “using the earth’s limited resources in a sustainable manner while minimizing impacts on the environment”. Bricks that cause less environmental impact during their life cycle may be called as resource-efficient bricks (REBs). Some of the key features of resource efficient bricks are:

  • Bricks that consume less primary material (e.g. clay, sand, limestone, etc.) for production
  • Bricks that utilizes waste materials for production
  • Bricks that requires less energy during manufacturing and result in less CO2 emissions and air pollution
  • Bricks that are produced using local raw materials and are consumed locally and in the process the transport requirement are minimized.
  • Bricks that have good thermal insulating properties which helps in reducing heat gains or loss from the wall thus improving thermal comfort and reduce the energy use in heating or cooling of buildings
  • Bricks which after the demolition of the building can be recycled or reused.


Figure 1 Key features of resource efficient bricks
Figure 1 Key features of resource efficient bricks

Can you provide some examples of resource efficient bricks ?

Burnt clay hollow and perforated bricks, compressed stabilized earth blocks, hollow concrete blocks, AAC and CLC blocks and fly ash bricks are some of the examples of resource efficient bricks. Most of these materials results in 20-60% reduction in energy consumption and CO2 emissions compared to the solid burnt clay bricks. AAC and hollow burnt clay bricks are light- weight and have good thermal insulation properties. AAC blocks and fly-ash bricks can use up to 60-80 % of industrial waste like fly ash, thus reducing the requirement for primary raw material to a great extent.

What is the status of resource efficient brick production and utilization in India?

The total production of resource efficient bricks in India is estimated to range between 30-40 billion bricks/ year and make up for 10-15% of the total market for bricks.

  • AAC blocks find main applications in medium/high rise housing in all major cities. Pune, Surat, NCR and Hyderabad are the main hubs to manufacture AAC blocks.
  • Hollow burnt clay blocks are used both for medium/high rise housing as well as individual houses Their production and application of these is concentrated in the southern states of Karnataka, Kerala and Tamil Nadu.
  • Fly ash bricks are used in all types of housing projects, particularly in the housing constructed by the government and public sector. Andhra Pradesh, Telangana, Maharashtra, Odisha are some of the main hubs to produce fly ash bricks.
  • The application of CSEB is mainly confined to low rise housing and individual houses. The know-how for the production and application of CSEB is confined to certain places, such as, Puducherry, Bengaluru, Kutch, etc.

What can be done to increase the utilization of resource efficient bricks in housing in India ?

The application of resource efficient bricks has been well demonstrated in the country. The utilization of resource efficient bricks is essential for reducing the carbon intensity in housing. In general, up to 20-30% reduction in embodied energy and carbon are possible using resource efficient bricks. An integrated action plan is needed to promote both the production and utilization of resource efficient bricks in housing. The selection of resource efficient bricks will vary from region to region as well as will also depend on the type of construction. While fly ash bricks, burnt clay perforated bricks and CSEB are more suited for low-rise load bearing or framed masonry construction to be undertaken in rural areas and small towns; AAC blocks and burnt clay hollow blocks are more suitable for mid and high-rise housing construction in metro cities and large urban centres. Indo-gangetic plains which has good availability of brick earth, is the main region where the production of burnt clay hollow blocks needs to be promoted. The production of the AAC blocks needs to be promoted in regions which are near to the power plants where fly ash is available. While actions like providing assured access to raw materials and financing are needed to promote production of resource efficient bricks. Awareness generation amongst architects and builders about the advantages of resource efficient bricks along with the training of civil engineers and masons is needed to increase the demand. Regulatory interventions in which the building bye-laws are amended to make the utilization of resource efficient bricks mandatory in housing would also go a long way in promoting these materials for housing.