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Property plus articles Property plus articles Document Transcript

  • Date:28/08/2004 URL:http://www.thehindu.com/thehindu/pp/2004/08/28/stories/2004082800430100.htm Heat-proof your houseIs your building equipped to handle those scorching rays of the sun? A. C. RAVIRANGASWAMI elaborates on the subject of thermal insulation.WE ALL know that the temperature inside and outside a building is different. Heat isallowed to pass rapidly through some building materials but some other materials do notallow heat to pass. The term `thermal insulation is used to indicate the techniques bywhich transmission of heat through the building is reduced.Besides enormous savings in electricity cost, an external thermal insulation enhances in asignificant way the comfort in a building, provides a healthier environment and helps inminimising damage to buildings.The effectiveness of thermal insulation is directly proportional to the type of material andits thickness, measured in terms of thermal conductivity.Thermal conductivity is the amount of heat in kilocalories that will flow through a givenmaterial in a given period of time. Thermal conductivity of a material depends on itsdensity, porosity, moisture content and temperature.The choice of the insulating material depends on the area to be covered and the cost ofheating or cooling. There are various types of insulation materials (see table).In the case of building protection, the following methods of thermal insulation arenormally used:Surkhi or brick bat cobaSurkhi is an artificial pozzolana made by powdering burnt bricks. In older times, in ourold structures, a very special lime surkhi was used, which was successful, but it neededvery skilled and experienced people.In fact, they belonged to the families practising such crafts and we do not have that kindof trained craftsmen now.
  • Brick jelly concreteWhile brick bat coba was common in the north of India, Brick Jelly Concrete, made withbroken bricks, lime, kadukkai, jaggery and so on, was preferred in the south. Like thelime surkhi, this was also successful because of the sincere labour and plenty of timeavailable.But due to lack of quality labour, materials and paucity of time, this system is notsuccessful.The surkhi and brick jelly concrete were used to provide slopes on the flat terraces foreasy draining of rainwater and also some sort of poor insulation.In India, sometimes it is accepted as a standard waterproofing system. It is very commonthat the screen provided over the brick concrete cracks because of non-compatibility ofsurkhi / brick jelly concrete with cement. These cracks allow ingress of water, whichtravels through the brickbat (which is so porous) to the RCC slab. This whole processresults in the failure of the waterproofing system and the slab starts leaking.It is found that generally, bitumen felt is applied on roof surfaces, which have a failedsurkhi or brick jelly concrete system.Bitumen or bitumen felt is no solution as the bitumen tends to crack due to theoxidation/UV radiation in a couple of seasons and in fact worsens the situation.ThermocolThe problems with thermocol are not very different from those in using surkhi / brickjelly concrete. In fact, once the water enters through thermocol, it starts absorbing water,ultimately rots and affects the reinforcement and the slab.Vermiculite or perlite concrete roof decksThese products are lightweight materials and are good for thermal insulation. But thesematerials when used for roof decks do pose some problems. Since they are soft materials,they need to be covered by tiles or some other hard material to make the surfacetrafficable. Vermiculite is very porous and needs effective waterproofing.Ceramic coatingsThe unusual insulating and corrosion-resistance properties of these products areexcellent. The ceramic compound with a high quality acrylic binder provides elasticityand a strong adhesion. The reflective ability of the ceramic compound will reflect asmuch as 96 per cent of heat wave reaching the surface where applied, thus lowering theconductive transfer of radiant heat to the inside.
  • Latest developmentsExperts are convinced that a typical thermal insulation product which is to be applied onthe flat terrace must possess the following qualities: Other than providing good thermalinsulation, it should be non-toxic, fire-resistant, have the ability to bond with almost anysurface, act as a barrier against early water penetration, reflect harmful UV rays and beable to take durable, anti-skidding coatings as the final component.A product has been developed based on these requirements. This product is acombination of lightweight materials along with redispersable polymer powders thatworks as a binding agent in cement-based dry mix mortar.The mortar consists of cement, fillers, additives, admixtures and polymer binding agents.A few companies in the weatherproofing business are presently testing the product inIndia.(The author is a Chennai-based weatherproofing consultant)© Copyright 2000 - 2008 The Hindu
  • Date:29/05/2004 URL:http://www.thehindu.com/thehindu/pp/2004/05/29/stories/2004052900010100.htm Is your house water-proof?Buildings incorporate latest scientific methods to ensure perfection in appearance whilewaterproofing is done by methods that are centuries or possibly millennia-old. Freneticspeed, non-availability of quality construction materials and lack of sincere labour arereasons for poor structures coming up of late, says A. C. RAVI RANGASWAMI Laying of tiles on a waterproofed terraceCONSIDER a house that you are visiting. It is less than a year old. Its façade isimpressive. Its design is ornate and available space has been skilfully exploited. Youadmire the beautiful and apt colours used too. But as you look up, at the ceiling, you finda damp patch in a corner, spoiling the whole appearance of the room. No expense hasbeen spared to make the house look grand but have the architect and builder been remissin bestowing attention on the durability of the structure?The small patch in the ceilingdoes not mean that water has leaked through that spot alone. It means rather, that waterspreading over a longer area and through various channels behind and below the surface,has, for the present, been able to escape to the surface at that point only. Obviously, stop-gap repair work to clear that blemish will not help, for, over a period of time, perhapsafter the very next shower, the moisture will find other portals of entry to the surface ofthe walls and ceilings.What then, is the source of this evil? Why is this leakage of water, even in new buildings,a ubiquitous problem in Chennai? The answer is that waterproofing of buildings receivesscant, if any, attention at the time of construction. While other aspects of the building
  • incorporate latest scientific methods to ensure perfection in appearance and quality,waterproofing is done following methods that are centuries, possibly millennia old.In those days, construction was done at a leisurely pace. Curing of concrete/mortar wasgiven great importance. Curing is one of the most important factors determining thestrength and water tightness of concrete. But nowadays, we witness huge buildingscropping up within a few months.The main reason for waterproofing being accorded step-motherly treatment is lack ofawareness of its long-term benefits.Waterproofing is an integral part of the construction activity and its critical role must beappreciated. We fail to realise that all the money we spend on aesthetics will go down thedrain if we do not ensure that the house is waterproofed. This is confirmed by the absenceof waterproofing details in the advertisements released by construction companies thatprovide all other details, which are physically visible.Water seepage is just not an inconvenience but also damages your concrete, causingcorrosion of steel reinforcement. Durability of the finished structure relates to concretesability to preserve the alkaline environment around the reinforcement during its servicelife and to maintain its structural capacity. The protection of the reinforcement is lost ifharmful substances like chlorides or carbon-dioxide and other toxic gases like nitrogenoxide and sulphuric oxides penetrate the cover layer along with moisture and oxygencausing corrosion of the re-bars.Frenetic speed of construction, non-availability of quality construction materials and lackof sincere labour are reasons for poor structures coming up of late.Although `Envelope Waterproofing of a structure is very much advisable, the mostvulnerable or important areas from the waterproofing angle are the roof and the sunkenportions of the toilets/bathrooms. The conventional method adopted is the brick-jellyconcrete or the brick bat coba. The brick-jelly concrete is very much suited for theMadras terrace, which has been forgotten with the development of concrete technology.
  • Slope-making (with concrete) towards downtake pipesWith the advent of practice of providing RCC roof slab on which brick-jelly concrete orbrick bat coba is provided, leaking roofs have become very common. A commonmisconception is that brick bat coba with the cement finishing of IPS is an adequatewaterproofing cover/treatment to terrace slabs.As a matter of fact, brick bat coba is a highly absorbent material and when water startsentering, it only works as a reservoir of water because of the absorbency of bricks. As aresult of stagnation of water in the brick bat coba, there is a heavy strain on the roof slab.Moreover, the trapped water finds its way to the slab below and seeps through weakareas. This is due to the fact that the roof slab has not been waterproofed. Waterproofingof sunken portions requires considerable expertise. If the waterproofing content of astructure is entrusted to a specialised agency or technician, better results ensue.Chemical Waterproofing: Chemical admixtures are ingredients in the form of powderor liquid, added to the concrete matrix during mixing. Admixtures are actually nosubstitute to waterproofing of buildings but definitely provide many beneficial effects.Coatings/Membranes: The advent of coating membranes followed admixtures butunfortunately they are not found suitable for Indian conditions. In surface coating, thepores and capillaries are blocked, hampering the natural breathing of the building. Theimpermeable surface coating allows water to build up behind the surface coating with therisk of disruption to the coating and possibility of damage. In fact, trapped water wouldbe moving behind surface coating and wherever it finds weaker segments, it would comeout resulting in cracks and blisters on the surface.Bitumen or asphalt is widely used as a coating. Bitumen, on attaining high temperature,particularly in summer, undergoes photo-oxidation, initiated by UV radiation. Thisresults in the formation of cancer-causing and toxic polyaromatic compounds including
  • Benzopyrene (B) (a harmful toxic constituent as in cigarette smoke) which have led to thebanning of bitumen in several countries.Polymer Flexible Slurries/Membranes: The proportion of polymer in these is at least40 per cent, expressed in terms of cement. As a result, the cement no longer forms a firmframework. In fact, the polymer bonds the mixture of sand and cement to yield a soft andflexible structure.Elastomeric Coatings/Membranes: The entry of recent generation of elastomericcoatings/membranes has revolutionised the waterproofing industry. These elastomers arespecial class of materials that are flexible and breathable, with high elongation andweatherability and crack bridging membranes.Impregnants: Solvent-based impregnants have several problems — Toxicity, hazardous,environmental pollution, odour and so on. In various countries, there is now legislation inplace limiting the use of organic solvents in the coating and impregnant industries.In the West, experts recommend solvent-free acqueous silicone ester emulsion forwaterproofing of external brick walls and exteriors without leaving any patch. At present,this product is manufactured as well as imported into our country.A majority of the products available in India are based on the coating technique, whilethe latest impregnation technique is offered by only a few companies. Some of the majorplayers in the waterproofing industry are Fosroc, Roffe, Mc Bauchemie, Pidilite, STP,Don, Xypex, Tech-Dry etc. As far as Chennai is concerned, the coating technique ispreferred since it is a one-step treatment and less time-consuming. Application of polymer modified coating helps to avoid water penetrationThe impregnation technique, which is becoming popular worldwide, is a multi-steptreatment and several civil engineering professionals are really impressed by the results
  • of this technique and recommend it to their clients. But, it must be borne in mind thatapplication skills play a very important role in the success of any waterproofing system.It calls for considerable expertise and specialised labour.The cost of waterproofing, compared to the spread over entire cost of the project, doesnot come to even 2.5 per cent.If you add the cost of interiors to the basic cost of the structures, then possibly thisadditional cost will be further lowered down to 1 per cent or 1.5 per cent.Further, as the number of floors increase, the cost per sq.ft. goes is further down to almosta negligible percentage. Thus, wise is the builder who acknowledges and implements theeffective safety measures for waterproofing right at the concept stage itself.(The author is a waterproofing consultant based in Chennai)© Copyright 2000 - 2008 The Hindu
  • Date:26/03/2005 URL:http://www.thehindu.com/thehindu/pp/2005/03/26/stories/2005032600080100.htm Cool your roof this summerAs the mercury levels rise, its time to look upwards at your roof for keeping your housecool. A. C. RAVI RANGASWAMI discusses ways to beat the impact of the scorchingsun on your roof.IT IS well known that Chennai has but one season extending through most of the year.The old joke among foreigners visiting Chennai that the city has three seasons, namelyhot, hotter and hottest, is in fact a fair representation of the weather conditions here.And we are now entering the hottest — which is also the longest — phase of the year.During this period, the heat outside is oppressive and the heat and stuffiness inside thehouse reach intolerable limits. The roof above our heads seems to magnify the effects ofthe suns radiation significantly. How, and why is this so?Ever since construction of houses on modern lines began, buildings have beenconstructed without using any material that will reduce the heating up of the interior ofthe house. The simple reason for this is that there has been no such material available tillnow.In a hot city like Chennai, a portion of the suns incident energy inevitably finds its wayinto the buildings on which its rays fall. In the summer time, this unwanted heat energycauses discomfort and requires the use of extra energy for air-conditioning. As thesummertime sun rises high in the sky, the suns radiant energy falls mainly on the roof,with east and west walls of buildings also receiving a significant share.
  • On warm summer days, the air in urban areas can be 5 degrees centigrade hotter than itssurrounding areas. Scientists call these cities `urban heat islands. The causes of the `heatisland effect include (a) dark surfaces — that absorbs more heat from the sun — asanyone who has worn a black t-shirt on a sunny day knows and (b) less vegetation thatwould provide shade and cool the air.Thus, the higher temperature in `urban heat islands increases air-conditioning costs andraises pollution levels. According to scientists in the U.S., dark roofs are heated by thesummer sun and raise the summertime cooling demand of buildings.For untreated normal roofs, the surface temperature is up to 25 degrees centigrade higherthan the ambient peak temperature. In roofs that have been heat-proofed, the differencebetween the roof and ambient temperatures can fall to as low as 10 degrees centigrade. Inother words, the room temperature can be effectively lowered by as much as 15 degreescentigrade.For this reason, `cool roofs are effective in reducing cooling energy use. Individualenergy savings depend on many factors, including geographic location and climate,existing insulation levels in the building, the type of roof installed and its upkeep.The Environmental Protection Agency in the USA says that in the right situations,cooling energy savings can be as high as 50 per cent. There is lot of research going on inthe USA in this direction and it is estimated that cool roofs can reduce the heat islandeffect and result in national energy savings to the tune of $750 million per year.Awareness of `cool roofs is very much less in India. Being a developing country, it ishigh time planners and individuals started thinking on the lines of Americans. As a firststep, planners and architects should focus on increasing the albedo (solar reflectivity) ofroofs which can limit or reverse an `urban heat island effectively and inexpensively.
  • These practices, when widely used in a community, can decrease air temperature andcooling demands, which also reduces the amount of smog in the air and result insignificant reduction in ozone concentration.In Chennai, the most common roof surface is the red clay tile (laid on brick jelly concreteused for creating slopes) which has a solar reflectance of 20 - 30 per cent. Instead, if awhite tile is used, solar reflectance will go up to 70 per cent which will definitelyimprove the convenience levels. This will result in a drop in peak cooling demand by 15per cent, meaning that the capacity of a buildings HVAC system can be downsized.Hence, it is evident that energy-efficient roofing systems can reduce roof temperaturessignificantly during the summer and thus reduce the energy requirements for air-conditioning.Roofs undergo significant expansion and contraction as they heat and cool throughout theday. Heat absorbed by the roof can also accelerate degradation by ultraviolet rays andwater. A reflective roof can reduce the amount of thermal shock that occurs on the roofsurface and make the roof last longer.Various materials have been tried in the past as thermal insulators with varying efficacy.Examples include thermocol, PUF and certain minerals such as Vermiculite and Perlite.These materials are all uniformly porous and structurally weak. Their effectiveness asthermal insulators get eroded as the pores get blocked over time. Moreover, theseproducts have to be installed at places where there is no load on the materials, e.g., falseceiling. Some of these materials also carry the hazard of being inflammable.To come to terms with the severity of the Indian summer, lot of research has been carriedout and scientists are of the view that the roof tile, in addition to being white in colour(which will absorb less sunlight than the conventional red clay tile), should retard theheat flow and be non-porous, strong and inflammable.New productRecently, a product — white tiles made of some specific minerals, metals and clay —which comes the closest yet to being the ideal thermal insulator for Indian conditions hasbeen developed after painstaking research. The trials were carried out in Morvi, Gujarat,where the temperature in summer often goes above 45 degrees centigrade. During thetrials, the following facts emerged: More than 70 per cent of heat enters the buildingthrough the roof; about 15 per cent enters through the windows facing the direct sunlight;about 10 per cent enters through the walls, and the top surface of the slab gets heated upto 65 Deg. C in summer.The conclusions were based on temperatures of the slab, walls and the windows takenduring various times during the day and night.After the newly developed tiles were installed, the temperature of the top surface did notexceed 50 Deg. C. In addition to the tile, the study team also developed a system of
  • ventilation, which, when supplemented would enhance the comfort levels inside to suchan extent that there is almost no need for air-conditioning.By logically applying design principles that capture natural breezes and the suns energy,electricity used in buildings can be reduced considerably which will result inimprovement of the environment and strengthening of the economy by drastically cuttingdown the need for nuclear energy and fossil fuels.(The author is a weatherproofing consultant)© Copyright 2000 - 2008 The Hindu