What’s good insulation?

Many architects use imported, expensive and environmentally inappropriate material

By Avikal Somvanshi
Last Updated: Sunday 28 June 2015

WhatÔÇÖs good insulation?

Cavities in the walls insulate an apartment in Bellary, Karnataka (Photo by:Ashok B Lall)

Walls and roofs of a building should be built in a way that its indoor temperature is not disturbed and the extreme heat or cold outside does not intrude, say architects. But this basic wisdom is now on a market overdrive as a large number of insulation products have flooded the market. This market, expected to be worth Rs 3,550 crore ($670 million) by 2015, is booming at an unprecedented rate of 20 per cent a year, states a report by the Tata Strategy Management Group and FICCI released in October this year.

Poorly insulated buildings are difficult to air-condition and lead to high energy loss. The market is, therefore, abuzz with products that can be padded to the walls to improve buildings’ thermal insulation. These include hazardous materials like mineral wool, rock wool, vermiculite, foams, expanded polystyrene and extruded polystyrene. Market is also agog with technologies like vacuum and gas insulations. But this pushes for more air-conditioners when the need is to improve the design and make the buildings naturally comfortable.

The push mostly comes from energy regulations for buildings. The energy conservation building code of Bureau of Energy Efficiency (BEE) has prescribed the minimum thermal resistance, called R-value, for walls and roofs. "Although the R-values are much higher than anything you can get with traditional solutions, they make eminent sense for air conditioned buildings” says Kolkata- based architect Laurent Fournier. He finds fixed values justified only for big luxury air conditioned buildings.

imageHigh R-value, he says, does not mean high comfort. In non-air-conditioned buildings, techniques like shading and ventilation play a major role in improving a building’s comfort value.

But R-value has become the new mantra, with green rating agencies like LEED, GRIHA and BEE’s star rating vouching for higher insulation. India finds itself disadvantaged because imported, expensive and environmentally inappropriate material is being shoved in.

Worse, dependence on them has deflected the market’s attention from creative cooling designs. “For high-level insulation efficiency, inner walls must be separated from the exterior surface, which is exposed to weather conditions, just like a Thermos flask,” says Richa Joshi, architect planner.

Traditionally, in hot-dry and composite climates of north India, building had thick mud or stone walls with roofs of mud and grass sandwiched between timber and terracotta tiles to keep the heat out. These are still effective in the cool interiors of the havelis of Rajasthan. In hot and humid climates, architects make use of natural ventilation with light construction and high roof of organic material like thatch, keeth (interwoven coconut leaves) or plain terracotta tiles. These can be seen in the houses of Kerala and Tamil Nadu.

Thermal performance of modern buildings can be improved with intelligent architecture. Replacing conventional material like brick and concrete with autoclaved aerated concrete blocks, hollow blocks or other material with inherent higher R-values can also improve buildings’ insulation. Designs like filler slabs, double roof, cavity walls, composite walls and shadings also help insulate houses.

“Some of our traditional insulation systems like cavity wall may be low on R-value but have lesser embodied energy and are long-lasting compared to high- performance insulation products,” says Deependra Prasad, an architect based in Delhi.

Synthetic insulation products like glass wool and rockwool are carcinogens, says Fournier. “Thermocol (polystyrene) is worse as it is less stable than glass and other wools, and releases gases. I prefer to keep these out of my and my client’s houses,” he says. The US Department of Health and Human Services admits that enough research on health hazards from synthetic insulation products has not been done yet.

“Dependence on import and expensive technology transfer should be minimised,” says Delhi-based architect Ashok B Lall. “Efforts are required to reduce the use of resource-guzzling air-conditioners through good insulation, and not use insulation as an excuse to increase the numbers of air-conditioners,” he adds.

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  • Is there any option to use

    Is there any option to use traditional method in modern building like highrise..???

    Posted by: Anonymous | 8 years ago | Reply
  • Dear Prashant, Thank you for

    Dear Prashant,

    Thank you for asking such a wonderfully relevant question. Let me attempt answering it. First of all we need to define high rise building since the insulation solution will be largely dependent on this. Options available for a 10 storied building will be different from a 50 storied building. Further insulation solutions for letÔÇÖs say a 163 storied Burj Khalifa in Dubai would be very different from other high rises. But we are not discussing Burj Khalifa here.

    In fact most of our current high rise buildings are in range of 10-40 stories. Traditional techniques cannot possibly be employed in their original schemes for such evolved architecture as the high rise. And this is a range where a curious and creative mix of our traditional and low cost technologies can be very well applied. It is also dependent on the kind of building envelop i.e. glazed, metal clad or brick/concrete. If the building envelop is a mix of windows and walls, by replacing convention burnt bricks or poured concrete with AAC blocks or hollow blocks or even cavity wall will improve the insulation of the envelop. (A 9 inch thick AAC block will have R-value of 9 while a similar brick wall is 4 R-value.) My advice is that the high embodied energy sheet insulation should be the last option, after you have exhausted your design palate.

    Glass or metal clad buildings are anyway not prescribed for Indian climate. And if you insist on using them it would be comparable to something like breaking ones spinal cord and then looking for the best wheel-chair to make oneself mobile. (by the way there are many energy efficient wheel chairs in market, if you can afford them) I understand the market dynamics and thick envelops for buildings are looked as wastage of sale-able floor area. So what is the way out?

    Now letÔÇÖs talk about something interesting brought to my notice by Fournier, everyone especially architects and builders know this clause in building codes which allows structural overhangs less than 2 feet in all buildings and this space is free of FSI. Thanks to Hafeez Contractor, who understood the tolerance in the building code for protruding decorative elements (like columns, etc.) that are not included into the floor area, allowing him to design his buildings like a sculpture, without wasting any sale-able floor area for his client. And what we get is finally a come-back to the thick building envelope of the past, but in a very different fashion: The envelope is now hollow and the hollow part is considered as outside the official, legal floor area. This has now become the standard practice all over India. The advantage, if utilized cleverly, is that this can effectively add a great deal to the insulation of buildings including the high rise.

    If an architect wants there are a zillion options, we just need to stop being lazy and start thinking.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Thank u so much Avikal for

    Thank u so much Avikal for this quick reply I was looking forward to it. It answered my query.
    Thank u so much once again for such a nice article.
    Good Work ... KEEP IT UP...!!!
    plzz do some research on water proofing too...!!!

    Posted by: Anonymous | 8 years ago | Reply
  • Dear Prashant, Thank you for

    Dear Prashant,

    Thank you for your kind words.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Nice information and

    Nice information and interpretation, there are many materials which are already banned by many European nations. We are against the heavy use of Glass and ACP on facades but due to the amateur regulations of government it is too difficult for us to control.

    What I suggest for the insulation is different from the rest. Every house in Indian sub-continent(except in the coastal areas) should go below the ground, at least 1/3rd of the total height. I had suggested it in most of my designs and I think that it can be promoted in a better way. Hope you come up with a new article on this method too.

    Moreover, its our ill fate that we have not carried forward our vernacular architecture, we are superimposed by the technologies, irrespective of climatic conditions. Lets move back to past and learn the indigenous methods of insulation.

    Posted by: Anonymous | 8 years ago | Reply
  • Dear Madhav, It is good to

    Dear Madhav,

    It is good to know that you are exploring traditional ways of insulation in modern context. Your idea of 'going underground' to insulate buildings seems very interesting, in fact the thermal significance of having a portion of ones building inside the earth is massive and I was just talking about the same with architect Chitra Vishwanath. You can read what she has to say about this concept in our next issue. Meanwhile, do share more information about such innovations with us, post pictures of the project where you implemented such insulation measures.

    As for use of glass and ACP in building envelop, I believe it is still a choice which an architect has to make in consultation with his client. Government regulations have little role to play as most of them are still voluntary and don't promote glass or ACP. But yes they do very little in deterring people from using such resource wasting trend. Can you specify which regulation are you talking about, so that I can answer your question better.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Avikal, I find this

    Dear Avikal,

    I find this sentence is not entirely correct:

    "fixing one value (is) wrong because weather conditions across the country are different."

    It should be very clear that,

    1. From the copy I got hold of, there is no "one value" prescribed in the energy efficiency code, in fact the R-values are slightly differentiated for different climatic zones in India. So one can't say
    "fixing one value is wrong" because this seems to imply that the code has prescribed "one value" only.

    2. The high R-values prescribed make, as far as I know from my limited knowledge and experience, eminent ecological and economic sense for AC
    buildings. Since the energy-efficiency code is exclusively concerned with AC buildings I don't see any problem with the code.

    Now, to enter into more details of the discussion:

    While it is true that the R-values are so high and so close to each other that they are, in practice, as good as one single value, this is perfectly rational and sensible for AC buildings, because as a matter
    of fact, the local climate has less relevance for AC buildings than the insulation value. In fact, one can say that mechanical cooling has the effect of shifting the balance of the relative weight of comfort parameters, to increase the dependence on insulation only. Therefore the emphasis on insulation can't be criticised in isolation. This emphasis is perfectly rational and justified in an AC environment. If you want to change the paradigm you have to first turn off the AC and make bio-climatic buildings. In these buildings, the thermal insulation is only one of many parameters. This is famously illustrated by thick mud walls, which people believe have a high R-value whereas they have in fact a poor R-value, but the houses made of thick mud walls are so comfortable because of their high thermal mass (in hot and dry climates like Rajasthan, or cold to temperate climates like the some parts of the US, the UK or France) or high moisture-regulation capacity (in hot and humid climates like Medinipur in West Bengal).

    I would like to mention the following references for more details, theoretical as well as practical:

    1. Baruch Givoni (any of his books, and more particularly "man climate and architecture" and "passive low energy cooling in buildings")

    2. Jean-Louis Izard (several books in French, and also this great series of articles entirely available online:

    (Its in French but it is a truly exceptional, and free, series of articles)

    3. Tim Padfield and his incredibly rich website on "conservation physics" for everything related to moisture regulation:


    4. John Morony and his experimental study on adobe and mud plaster as moisture regulation material (although I am not convinced by Morony's claim that there is a phase change in mud walls):


    5. Areemit and Sakamoto, "Feasibility study of the passive solar room dehumidifying system using the sorption property of a wooden attic space through field measurement"


    (This rather specialised and technical study, is the most scientific I came across which is of direct interest for the issue of natural cooling in hot and humid climates, and I believe the effect evidenced
    by Areemit and Sakamoto is also active in vernacular architecture, like most traditional bengali houses with solid mud walls and a loft on a heavy floor creating a ventilated attic, similar to Areemit and Sakamoto's experimental set-up)

    Laurent Fournier

    Posted by: Anonymous | 8 years ago | Reply
  • sir i read ur down to earth

    sir i read ur down to earth article i really found it intresting... but do let me knw y we cant use glass wool as not good insulating material does it really harm the health.. who's staying the glass insulated building.so then acc to research onlycavity wall is the favourable materiall..........do let me knw abt dis ??and how we can remove the use of brick nd concrete in construction of modern building...except bamboo and alll.........nd hw we can insulate from the foundation......nd water proofing building material also..

    Posted by: Anonymous | 8 years ago | Reply
  • Here is some other



    Controlling humidity is as important, if not more, as controlling temperature for a comfortable and hygienic environment. I've seen several luxury AC homes were mould and fungus were happily growing...

    Posted by: Anonymous | 8 years ago | Reply
  • Thank you Laurent for

    Thank you Laurent for explaining the issue further.

    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Sid, LetÔÇÖs start by

    Dear Sid,

    LetÔÇÖs start by clarifying that glasswool insulated wall is not same as a curtain/structural glass wall. Glasswool is a compacted mat of really tiny glass fiber strains. This mat is normally padded upon the wall surface then plastered or covered by some cladding material. Thickness of the mat determines the insulation capacity or R-value of the wall. As this product is just a compacted mat of fine glass fiber, it readily releases these fibers into the air if disturbed in any fashion like drilling holes in wall, cracks in wall or even tapping on the wall among many others. These fibers are found to be carcinogenic if inhaled, thus raising health concern. In fact this problem is with all the mineral fiber products available for insulation, including rockwool and celluloidwool. Argument which most of the insulation companies give in favour of these products is that if properly installed and tightly sandwiched in-between layers of masonry they pose no health hazard. But quality of skill and seriousness exhibited by majority of our building sector in handling such complicated installation is matter of concern. Further during the occupancy of the building there is no way of controlling the damages or alterations to the wall which can release these fibers into the indoor air.

    Cavity walls are a low-tech solution and hold great possibility for better insulation, there surely should be more research in this direction. But they are not the only solution. Thermal comfort inside a building is governed by many factors and insulation is just one of the factors. In fact ventilation, shading among others play a very vital role, and in non-air-conditioned building are more vital factor affecting thermal comfort than insulation.

    Moving back to issue of glasswool, kind of insulation level required to make an air-condition building energy efficient cannot solely be achieved by cavity walls (at least by current technology). Thus options having lesser health hazard are available in market but they are not only really expensive but are more energy intensive and environment unfriendly petrochemical based sheets (polystyrene and polyurethane). So there is no magic solution. But if you plan to completely air-condition your building it make eminent sense to invest in these technologies, and more importantly in good quality workmanship for correct installation and maintenance. As it is logical if you spend millions on a good HVAC system a little extra expense on improving the efficiency of it in form of better insulation is good business.

    That being said an architect has means and ability to reduce dependency on such products by innovative and creative design interventions.

    I donÔÇÖt understand why you want to get rid of bricks and concrete from modern buildings. I understand they are not the best of building materials when it comes to overall environmental impact of them, but they are better option compared to glass clad buildings by any measure economic, environmental and comfort. In addition there are interesting new kind of bricks and block are coming in the market, something worth exploring.

    That brings me to issue of glass buildings which have caught the fancy of popular imagination. Glass envelop is not prescribed for hot tropical climate like we have here in India. A more detailed study on glass in building will be taken up in the next classroom, kindly wait for that.

    As for insulation of foundation, it is not recommended to insulate foundation in hot climatic zones, as foundation works as heat sinks and helps maintain the thermal balance of the building. In cold climate, where the major requirement is to keep the heat inside the building, one needs to insulate the foundation and floors.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Kindly send further details,

    Kindly send further details, if available, on your remark: "Thermocol (Polystyrene) is worse as it is less stable....and releases gases.."
    What kind of gases, under what conditions (only when burning?) If available I would appreciate any details on fire resistance, flame spread.
    Thanking you

    Posted by: Anonymous | 8 years ago | Reply
  • Hi Dorothee, Expanded

    Hi Dorothee,

    Expanded polystyrene, polyurethane, etc. are organic polymers (large molecules made by "polymerisation" from petroleum by-products), or "plastic". These organic polymers are not stable, their durability varies but is counted in years or in decades, not in centuries. Their decomposition is accelerated by heat, sunlight, acidic vapours, etc. and in the process of break-down of their molecules they release various gases which are generally harmful, carcinogenic, etc. The most simple evidence of these gases is the smell of plastics, which is obvious in many modern buildings when not sufficiently ventilated. It is well-known that modern buildings have more pollutants inside than outside. This is mostly because of all these gases released by the slow decomposition of plastics (including flooring, cladding, laminates, paints, glues, etc.). Plastics are also a liability from the fire safety point of view, as they not only fuel the fire but also release deathly gases by burning (as happened last year in a disastrous fire in a Kolkata hospital, where nearly 100 people died from poisonous gases but not from burns). As an alternative, natural fibers like rice husk or jute (or hemp in coutries like France where it is grown in large quantities), mixed with lime, make excellent, durable and healthy insulating materials. I used a 50% lime - 50% rice husk mix in my false ceiling in my own flat. I also used a 30% lime - 70% saw dust mix in a commercial project as roof insulation below the roofing tiles. Lime-hemp (or "hemcrete") is now a mainstream insulation material in France and the UK. Lime, rice husk, hemp, are insect-repellent and rodent-repellent, contrary to glasswool and polystyrene, which rodents use for their nests and is often found scattered by these animals all around the house when not properly sealed. These natural materials are also hygrophobic, they are water-repellent and do not attract moisture, thereby have no condensation problems unlike products like expanded polystyrene or glasswool. Natural fibers mixed with lime are also fire-retardant, they help protect the structure from fire instead of fuel the fire like polystyrene.

    Posted by: Anonymous | 8 years ago | Reply
  • Great article.. we also have

    Great article..
    we also have see an increasing demand of our 100% recycled plastics sheets which are used for roofing or insulation...
    they are great and reduce temperatures by over5Deg in hot/dry weather. esp good for cattle shed and poultry. also now being used in upmarket roof insulation.

    Posted by: Anonymous | 8 years ago | Reply
  • Laurent thank you for

    Laurent thank you for explaining the issue with polystyrene to Dorothee.

    Dear Dorothee, hopefully all your queries have been satisfactorily addressed by Laurent. Only thing I would like to add is that apart from health hazard polystyrene has very high environmental cost. Being a petrochemical based product, its production and disposal is highly polluting and resource intensive. Kindly refer the table and graph in the info-graphic to see how it compares to other insulation products.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Tushar, Thank you for

    Dear Tushar,

    Thank you for your kind words. I am a big fan of your recycled roofing sheets. In fact I lived under one for almost seven months in Auroville (Pondicherry) and found them very comfortable. So they are equally good for human in-habitation as for cattle and poultry in my personal opinion. Though I'm not aware how are these being used in upmarket roof insulation. Kindly share more information regarding these.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Dear Avikal, Thanks for your

    Dear Avikal,
    Thanks for your and Laurent Fournier's reply.
    I am aware of the high environmental cost because of high embodied energy of polystyrene.
    But I have been using waste packages of this material,crushed and mixed with cement so as to reduce the amount of waste which would here in Auroville otherwise have to go into a landfill.(The quantity of this material generated in this small community is staggering!)
    I have used it for roof insulation, and now also for walls. It has a high insulation factor in addition to being a very light weight filler, thus reducing structural requirements. Mixed with cement and plastered, I do not think there will normally be any evaporation of toxic gases. My main concern, as I have put into my query is the fire hazard. If you can help in any way to get some reliable info on this , or suggest a way to test and measure, I would greatly appreciate it.
    Thanks again, Dorothee

    Posted by: Anonymous | 8 years ago | Reply
  • Dear Dorothee, although I

    Dear Dorothee, although I don't know about the plastic-cement mix that you are using, I have mixed feelings about it. I understand that we have to choose between NOT using plastic AT ALL, which is very difficult, and accepting to bear the personal consequences of recycling, but I find it difficult to mix plastic with the building material of my (or other's) house! Frankly, I won't do that!

    Now about fire safety I think that is a genuine concern.

    I believe it is very technical and very costly to make a testing. It's done in large laboratories where special furnaces can subject the building element to be tested to accurate temperature curves, such as these:


    But you can also apply a coat of plaster on your wall to retard the action of fire. There are different values for different plasters. Gypsum is the best, lime-sand or lime-sand-gypsum a second best, clay and cement-sand are also good.

    I can't find the values now but you can find them on the net. I remember that 12mm of gypsum (POP or gypboard) is roughly equivalent to 1/2 hour fire resistance, so you have 1h for 25mm, 2h for 50mm, etc. It's not so good for other types of plaster. For 4 hours (a proper "fire wall") you need 0.5m of stone or brick masonry. But in practice in most building codes 1/2h is good enough for a ground floor building with no sleeping at night, and then the requirement increases with the number of storeys and whether people sleep at night or not, whether the building is open to the general public or is only open to staff, etc. See the National Building Code.

    Posted by: Anonymous | 8 years ago | Reply
  • I am working with farmers in

    I am working with farmers in rural areas to create low cost cold rooms to store vegetables.

    We are looking to construct these cold rooms in existing concrete structures. The cold rooms will be cooled to a temperature of 4-6 C and also need to retain high humidity levels. For insulation that we are being recommended range from Polyurethane foam to thermocol.

    The objective is to keep the cost low as well as try and use traditional material that is easily available, but the primary objective remains to maintain the low temperature and high humidity levels.

    What would be the right materials to use for insulation. Would the clay & lime mix mentioned above work.

    Appreciate your guidance.

    Posted by: Anonymous | 8 years ago | Reply
  • Hi Sriram, your question is

    Hi Sriram, your question is complex and exceeds my competence. I think with such a low temperature and such a high humidity level you have to be very careful with risks of condensation within the insulation. Condensation is to be avoided at all costs. I suggest you consult an expert. You can also try the WUFI-ORNL software, which simulates the heat and moisture transfer through composite wall assemblies. The simplified version is free, and you can maybe approach your assembly with similar materials/environmental conditions (like taking a cold and humid climate in the US for your interior ambiance, and a heated interior for your exterior ambiance). You can also check if you get any relevant information in the website of TIM PADFIELD on Eco-friendly conservation.

    Posted by: Anonymous | 8 years ago | Reply
  • In the item No.4 above I

    In the item No.4 above I doubted the claim by Moroni that mud/earth is a "phase-change material".

    However, I read recently several articles where the authors say they have evidence and measured phase change in lime-hemp concrete. That means that water evaporates and condenses within lime-hemp concrete as the temperature varies, and this contributes to the good thermal properties of this material. The authors say more research is needed to find out the effects of phase-change in other porous materials, like mud, straw, etc.

    Therefore John Moroni could be right after all!





    L. Arnaud, D. Samri (2005). Hygro-thermal behaviour of building porous materials, in Proc. Third Int.
    Biot Conference, Oklahoma (USA)

    D. Samri, L. Arnaud (2006). Assessment of heat and mass transfers in building porous materials.,
    Proceedings of the 4th European Conference on Energy Performance & Indoor Climate in Buildings,
    November 2006, Lyon.

    Posted by: Anonymous | 8 years ago | Reply
  • Hi Laurent, I live on the top

    Hi Laurent,

    I live on the top floor of a building in Mumbai, the sun rays hit my rooftop for the first half of the day only. I am currently using thermacol sheets as a rudimentary form of insulation between my ceiling and false ceiling. Reading about the carcinogenic effects that it might have has alarmed me. The terrace on my building has recently been water proofed with broken tiles. I plan to get the sheets removed and have 3 questions:-

    1. Do I need insulation between the ceiling and false ceiling?
    2. In what form is lime and husk mixture insulation available?
    3. How much would this cost?


    Posted by: Anonymous | 7 years ago | Reply
  • Dear Karan, We prepared the

    Dear Karan,

    We prepared the lime-rice husk mixture ourselves (me and my family). It was a 50% lime putty (matured under water for more than a week) and 50% rice husk. We ordered the rice husk from villagers in the Sundarbans, and we purchased the lime (unslaked lime, or quick lime) in a local construction shop. We made a temporary tank on the roof top of our buildings, using dry bricks and a plastic sheet, for slaking the lime. I have also used a lime - saw dust mixture in another project, and the ratio was 30% lime and 70% saw dust, so it was cheaper and lighter, for a mechanical resistance approximately equal to thermocol. But rice husk needs to be used in 50%-50% ratio to get the same strength.

    We then hanged a lattice made of bamboo strip ('durma') from the concrete slab, with gaps of about 1 inch between the strips, with hooks every 1 foot on a square grid, using the same hooks that serve for false ceilings.

    Then the really hard work started: pushing by hand small "saussages" of lime-rice husk mixture, between the gaps of the bamboo lattice, forming a 2-inches-thick layer above the lattice.

    We left an air gap of 2 inches between the RC slab and the lime-rice husk mix. (that means 4 inches between RC slab and bamboo lattice).

    The last step was plastering the whole thing from below with a 70% lime - 30% rice husk mix, and after a few days, white washing with lime.

    In the light of this experience, I would now create ventilators above the false ceiling, so that the very hot air that is forming in this space can be evacuated.

    However it works, the room is noticeably cooler, particularly at the head level, where the heat radiated from the bare RC ceilings of the other rooms of my flat create a sensation of 'pressure' during summer afternoons and evenings.

    Posted by: Anonymous | 7 years ago | Reply
  • Interesting article this. I

    Interesting article this. I will soon move to a top floor appartment in Bangalore. Any opinions on how to keep it cool during summers in an eco friendly and easy to implement way?

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Soubhik, Nice to hear

    Dear Soubhik,

    Nice to hear from you. To reduce the heat in your top floor you can employ any of the cool roof technology (explore http://www.downtoearth.org.in/content/cool-idea ) or you can opt for some really good techniques developed by Laurent which he has described in his responses in the comment section of this story itself.

    Feel free to contact me if you have further doubts.

    Thank you.


    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • I'm seeing builders install

    I'm seeing builders install 2-3 inch of thermocol and then 4 inch of mud/sand on top for residential flat roofs. Is this a good idea ?

    Posted by: Anonymous | 7 years ago | Reply
  • I've never seen that! Where

    I've never seen that! Where have you seen that?

    As far as I know, there are several tough technical issues with what you describe:

    1. Mud can be used only if it is protected by an additional layer, to prevent the mud from getting liquid and flow away. Mud is often used with just a mud plaster protection in regions where the rain is either scarce, or doesn't last for too many days in a stretch (even in some villages in Uttar Pradesh, for example in Agra district, where flat roofs covered with mud are still being used) but that entails a very susbtantial, serious, annual maintenance!

    2. I don't think sand can be used at all in this manner, because it will just flow away in an uncontrolable manner.

    3. Thermocol can be used, either above of below the waterproofing. If used above the waterproofing, it will protect the waterproofing and the supporting structure from large thermal stress, which is good. But the thermocol will absolutely need a good protection. This protection is generally a layer of 3''-thick PCC (plain concrete) with joints every 6 feet, and that entails using a very strong, high-density thermocal, capable of supporting permanently the load of the PCC. Ordinary thermocal won't do. Also you will need evacuation of water at 2 levels: 1. at the top of the PCC (for most of the water), and 2. below the thermocol (for whatever little water will seep through the joints). So it's a relatively complicated solution.

    4. Thermocol is often used as "underdeck insulation" as a low-cost solution for commercial projects. This solution can be justified economically for A.C. banquet halls or similar spaces where AC is needed but which are not used continuously. The advantage of underdeck insulation in these cases is that you don't have to cool the entire structure for a 4-hour programme, but just the air below the insulation. But in housing or spaces occupied continuously it doesn't make sense. "Overdeck" insulation is preferable. There are many solutions for that, thermocol is probably not the best.

    Posted by: Anonymous | 7 years ago | Reply
  • "Poorly insulated buildings

    "Poorly insulated buildings are difficult to air-condition and lead to high energy loss".
    Dear Avikal
    I am still searching for a theoretical basis that correlates building envelope insulation with energy consumed for space cooling (and heating).If we consider a building envelope which is poorly insulated but it is 'air-tight' would it always lead to high energy loss?

    Posted by: Anonymous | 7 years ago | Reply
  • Dear Seema, the first thing

    Dear Seema,

    the first thing to answer in your question is, "what do we want to achieve exactly?".

    I suggest you first look at the scientific basis of comfort by Nicol and Humphreys.

    The lecture below is a good point to start:


    After you have an idea of the kind of "gap" between comfort and discomfort that your building will have to bridge, depending of the season and time of the day, you can start looking for broad directions for solutions.

    For that, the "Mahoney Tables" can provide a starting point. They have been re-published recently in an old but still relevant, and very affordable book:

    Manual of Tropical Housing by Koenigsberg et al. Orient Longman

    Yet another, and generally better, starting point is a critical study of local vernacular architecture. It has always achieved a highly optimised balance between resources and needs in a particular context.

    Whenever I have checked, there was no difference between the recommendations of the Mahoney Tables and local vernacular architecture. The mechanical process of the Mahoney Tables can't of course be as accurate as an actual observation of vernacular architecture! But they provide a glimpse to the logic of it.

    And to refine further, you can get guidance from the research of Baruch Givoni for example.

    So you see that your question is dependant on many parameters and can't have a straight answer.

    But one thing is sure: NO air-tight building can be comfortable in ANY climate!

    The extremely rich website below, by Tim Padfield, has an observation on the abject failure of modern buildings when they are "designed like submarines":


    Posted by: Anonymous | 7 years ago | Reply
  • please see our new video on

    please see our new video on roof sheets made from post consumer recycled mixed plastics: https://www.youtube.com/watch?v=qYceNBStHnY

    Posted by: Anonymous | 7 years ago | Reply

    REDUCE ENERGY consumption by 20% BETTER THAN painting the ROOF WHITE
    abc Weather Proof SRI Tiles
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    Posted by: Anonymous | 7 years ago | Reply
  • Due to the humid condition,

    Due to the humid condition, many germs get stick to the human skin.
    As the warmer indoor air is passed through the ducts,
    the compounds inside absorb heat as they changes from liquid to gas. With the fan you could suffer from headache, but your body goes through its normal process of excreting while you are asleep.

    Posted by: Anonymous | 6 years ago | Reply
  • What would be best for roof

    What would be best for roof insulation of an 8-storied residential apartment building in Kolkata. Floor area 2400 sq ft (approx).

    Posted by: Anonymous | 6 years ago | Reply
  • I live in a first floor

    I live in a first floor apartment, have two floors above mine.
    My bedroom walls are east/southeast exposed.
    Adding to my trouble is the transformer of our housing society. Its located on the ground floor below us!
    What's the best insulation solution for my east/southeast facing walls? The wall are window less and approximately 250sqft area.

    My options for internal wall insulation:
    1. XPS on inner walls (check out www.insuboard.com)
    2. Another brick wall with a 1inch gap from the existing.
    3. Hemp create (unfortunately my research did not turn up any commercially available solutions)
    Note that I cannot remove the existing brick structure or change the outer wall finishing due to the housing society rules. My walls form the external facade of the building.
    Your opinion matters. Please share.


    PS: for the floor I chose regular wooden tiles, commercially available at a price upward of 100Rs per swift.

    Posted by: Anonymous | 6 years ago | Reply
  • hai, I am Dr.Satish and


    I am Dr.Satish and loooking for the best option for the terrrace for weather proofing it including water proofing. Just became a fan of yours after going through your blog. I reside in Bangalore and we as a whole family are very environmental conscious.


    Posted by: Anonymous | 5 years ago | Reply
  • Avikal, I am buying a


    I am buying a property on second floor in chennai.

    I am suspecting lot of heat in summer being top floor.

    My builder has told me that they will use white reflective tiles and it would be okay.

    I am not sure how much % of heat will be reflected and how much releif I will have due to these reflective tiles.

    Please help.

    Abhijeet K.

    Posted by: Anonymous | 5 years ago | Reply
  • Is there any economical method of thermal insulation below corrugated asbestos cement sheet. I ve also installed Everest grid ceiling with thermocole between ac sheets and grid ceiling but of no use in summer. Please suggest.

    Posted by: Rohan Sawant | 4 years ago | Reply
  • May I know about the sheet which is used before plastering the roof for insulation from the heat and making the room cool.
    After spreading the thermocol or other sheet, what type of tiles are used ? please advice.

    Posted by: Sunil Kumar | 3 years ago | Reply
  • Is there any research done or method to know which insulation to use on the basis of the Climate zone that area?

    Thank You
    Ratan Kuber

    Posted by: Ratan | 2 years ago | Reply
  • Thank you Avikal for this very informative article.

    I am into the food and catering business. Currently I am modifying an old cargo Van into a food truck. I am very keen on using safe materials in the food truck build.

    I will be doing Stainless steel sheet paneling for the interiors of the van. what kind of insulation material can i use in between the outer body and inner SS panel so that the van stays cooler inside.

    Right now i dont see much option here other than glass wool or Thermocol, PU foam etc.

    The material has to be as light as possible, as my vehicle has max payload capacity of 1200kg. I need to accomodate everything including heavy kitchen equipment within the payload capacity.

    please guide me.

    Thanks n regards,

    Posted by: Sumant | 2 years ago | Reply