1. Date:28/08/2004 URL:
http://www.thehindu.com/thehindu/pp/2004/08/28/stories/2004082800430100.htm
Heat-proof your house
Is your building equipped to handle those scorching rays of the sun? A. C. RAVI
RANGASWAMI elaborates on the subject of thermal insulation.
WE ALL know that the temperature inside and outside a building is different. Heat is
allowed to pass rapidly through some building materials but some other materials do not
allow heat to pass. The term `thermal insulation' is used to indicate the techniques by
which transmission of heat through the building is reduced.
Besides enormous savings in electricity cost, an external thermal insulation enhances in a
significant way the comfort in a building, provides a healthier environment and helps in
minimising damage to buildings.
The effectiveness of thermal insulation is directly proportional to the type of material and
its thickness, measured in terms of thermal conductivity.
Thermal conductivity is the amount of heat in kilocalories that will flow through a given
material in a given period of time. Thermal conductivity of a material depends on its
density, porosity, moisture content and temperature.
The choice of the insulating material depends on the area to be covered and the cost of
heating or cooling. There are various types of insulation materials (see table).
In the case of building protection, the following methods of thermal insulation are
normally used:
Surkhi or brick bat coba
Surkhi is an artificial pozzolana made by powdering burnt bricks. In older times, in our
old structures, a very special lime surkhi was used, which was successful, but it needed
very skilled and experienced people.
In fact, they belonged to the families practising such crafts and we do not have that kind
of trained craftsmen now.
2. Brick jelly concrete
While brick bat coba was common in the north of India, Brick Jelly Concrete, made with
broken bricks, lime, kadukkai, jaggery and so on, was preferred in the south. Like the
lime surkhi, this was also successful because of the sincere labour and plenty of time
available.
But due to lack of quality labour, materials and paucity of time, this system is not
successful.
The surkhi and brick jelly concrete were used to provide slopes on the flat terraces for
easy draining of rainwater and also some sort of poor insulation.
In India, sometimes it is accepted as a standard waterproofing system. It is very common
that the screen provided over the brick concrete cracks because of non-compatibility of
surkhi / brick jelly concrete with cement. These cracks allow ingress of water, which
travels through the brickbat (which is so porous) to the RCC slab. This whole process
results 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 failed
surkhi or brick jelly concrete system.
Bitumen or bitumen felt is no solution as the bitumen tends to crack due to the
oxidation/UV radiation in a couple of seasons and in fact worsens the situation.
Thermocol
The problems with thermocol are not very different from those in using surkhi / brick
jelly 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 decks
These products are lightweight materials and are good for thermal insulation. But these
materials 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 surface
trafficable. Vermiculite is very porous and needs effective waterproofing.
Ceramic coatings
The unusual insulating and corrosion-resistance properties of these products are
excellent. The ceramic compound with a high quality acrylic binder provides elasticity
and a strong adhesion. The reflective ability of the ceramic compound will reflect as
much as 96 per cent of heat wave reaching the surface where applied, thus lowering the
conductive transfer of radiant heat to the inside.
4. 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 while
waterproofing is done by methods that are centuries or possibly millennia-old. Frenetic
speed, non-availability of quality construction materials and lack of sincere labour are
reasons for poor structures coming up of late, says A. C. RAVI RANGASWAMI
Laying of tiles on a waterproofed terrace
CONSIDER a house that you are visiting. It is less than a year old. Its façade is
impressive. Its design is ornate and available space has been skilfully exploited. You
admire the beautiful and apt colours used too. But as you look up, at the ceiling, you find
a damp patch in a corner, spoiling the whole appearance of the room. No expense has
been spared to make the house look grand but have the architect and builder been remiss
in bestowing attention on the durability of the structure?The small patch in the ceiling
does not mean that water has leaked through that spot alone. It means rather, that water
spreading 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, perhaps
after the very next shower, the moisture will find other portals of entry to the surface of
the 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 receives
scant, if any, attention at the time of construction. While other aspects of the building
5. 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 was
given great importance. Curing is one of the most important factors determining the
strength and water tightness of concrete. But nowadays, we witness huge buildings
cropping up within a few months.
The main reason for waterproofing being accorded step-motherly treatment is lack of
awareness of its long-term benefits.
Waterproofing is an integral part of the construction activity and its critical role must be
appreciated. We fail to realise that all the money we spend on aesthetics will go down the
drain if we do not ensure that the house is waterproofed. This is confirmed by the absence
of waterproofing details in the advertisements released by construction companies that
provide all other details, which are physically visible.
Water seepage is just not an inconvenience but also damages your concrete, causing
corrosion of steel reinforcement. Durability of the finished structure relates to concrete's
ability to preserve the alkaline environment around the reinforcement during its service
life and to maintain its structural capacity. The protection of the reinforcement is lost if
harmful substances like chlorides or carbon-dioxide and other toxic gases like nitrogen
oxide and sulphuric oxides penetrate the cover layer along with moisture and oxygen
causing corrosion of the re-bars.
Frenetic speed of construction, non-availability of quality construction materials and lack
of sincere labour are reasons for poor structures coming up of late.
Although `Envelope Waterproofing' of a structure is very much advisable, the most
vulnerable or important areas from the waterproofing angle are the roof and the sunken
portions of the toilets/bathrooms. The conventional method adopted is the brick-jelly
concrete or the brick bat coba. The brick-jelly concrete is very much suited for the
Madras terrace, which has been forgotten with the development of concrete technology.
6. Slope-making (with concrete) towards downtake pipes
With the advent of practice of providing RCC roof slab on which brick-jelly concrete or
brick bat coba is provided, leaking roofs have become very common. A common
misconception is that brick bat coba with the cement finishing of IPS is an adequate
waterproofing cover/treatment to terrace slabs.
As a matter of fact, brick bat coba is a highly absorbent material and when water starts
entering, it only works as a reservoir of water because of the absorbency of bricks. As a
result 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 weak
areas. This is due to the fact that the roof slab has not been waterproofed. Waterproofing
of sunken portions requires considerable expertise. If the waterproofing content of a
structure is entrusted to a specialised agency or technician, better results ensue.
Chemical Waterproofing: Chemical admixtures are ingredients in the form of powder
or liquid, added to the concrete matrix during mixing. Admixtures are actually no
substitute to waterproofing of buildings but definitely provide many beneficial effects.
Coatings/Membranes: The advent of coating membranes followed admixtures but
unfortunately they are not found suitable for Indian conditions. In surface coating, the
pores and capillaries are blocked, hampering the natural breathing of the building. The
impermeable surface coating allows water to build up behind the surface coating with the
risk of disruption to the coating and possibility of damage. In fact, trapped water would
be moving behind surface coating and wherever it finds weaker segments, it would come
out 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. This
results in the formation of cancer-causing and toxic polyaromatic compounds including
7. Benzopyrene (B) (a harmful toxic constituent as in cigarette smoke) which have led to the
banning of bitumen in several countries.
Polymer Flexible Slurries/Membranes: The proportion of polymer in these is at least
40 per cent, expressed in terms of cement. As a result, the cement no longer forms a firm
framework. In fact, the polymer bonds the mixture of sand and cement to yield a soft and
flexible structure.
Elastomeric Coatings/Membranes: The entry of recent generation of elastomeric
coatings/membranes has revolutionised the waterproofing industry. These elastomers are
special class of materials that are flexible and breathable, with high elongation and
weatherability 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 in
place limiting the use of organic solvents in the coating and impregnant industries.
In the West, experts recommend solvent-free acqueous silicone ester emulsion for
waterproofing 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, while
the latest impregnation technique is offered by only a few companies. Some of the major
players 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 is
preferred since it is a one-step treatment and less time-consuming.
Application of polymer modified coating helps to avoid water penetration
The impregnation technique, which is becoming popular worldwide, is a multi-step
treatment and several civil engineering professionals are really impressed by the results
9. Date:26/03/2005 URL:
http://www.thehindu.com/thehindu/pp/2005/03/26/stories/2005032600080100.htm
Cool your roof this summer
As the mercury levels rise, it's time to look upwards at your roof for keeping your house
cool. A. C. RAVI RANGASWAMI discusses ways to beat the impact of the scorching
sun 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, namely
hot, 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 the
house reach intolerable limits. The roof above our heads seems to magnify the effects of
the sun's radiation significantly. How, and why is this so?
Ever since construction of houses on modern lines began, buildings have been
constructed without using any material that will reduce the heating up of the interior of
the house. The simple reason for this is that there has been no such material available till
now.
In a hot city like Chennai, a portion of the sun's incident energy inevitably finds its way
into the buildings on which its rays fall. In the summer time, this unwanted heat energy
causes discomfort and requires the use of extra energy for air-conditioning. As the
summertime sun rises high in the sky, the sun's radiant energy falls mainly on the roof,
with east and west walls of buildings also receiving a significant share.
10. On warm summer days, the air in urban areas can be 5 degrees centigrade hotter than its
surrounding areas. Scientists call these cities `urban heat islands.' The causes of the `heat
island effect' include (a) dark surfaces — that absorbs more heat from the sun — as
anyone who has worn a black t-shirt on a sunny day knows and (b) less vegetation that
would provide shade and cool the air.
Thus, the higher temperature in `urban heat islands' increases air-conditioning costs and
raises pollution levels. According to scientists in the U.S., dark roofs are heated by the
summer sun and raise the summertime cooling demand of buildings.
For untreated normal roofs, the surface temperature is up to 25 degrees centigrade higher
than the ambient peak temperature. In roofs that have been heat-proofed, the difference
between the roof and ambient temperatures can fall to as low as 10 degrees centigrade. In
other words, the room temperature can be effectively lowered by as much as 15 degrees
centigrade.
For this reason, `cool' roofs are effective in reducing cooling energy use. Individual
energy 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 in
the USA in this direction and it is estimated that cool roofs can reduce the heat island
effect 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 is
high time planners and individuals started thinking on the lines of Americans. As a first
step, planners and architects should focus on increasing the albedo (solar reflectivity) of
roofs which can limit or reverse an `urban heat island' effectively and inexpensively.
11. These practices, when widely used in a community, can decrease air temperature and
cooling demands, which also reduces the amount of smog in the air and result in
significant reduction in ozone concentration.
In Chennai, the most common roof surface is the red clay tile (laid on brick jelly concrete
used for creating slopes) which has a solar reflectance of 20 - 30 per cent. Instead, if a
white tile is used, solar reflectance will go up to 70 per cent which will definitely
improve the convenience levels. This will result in a drop in peak cooling demand by 15
per cent, meaning that the capacity of a building's HVAC system can be downsized.
Hence, it is evident that energy-efficient roofing systems can reduce roof temperatures
significantly during the summer and thus reduce the energy requirements for air-
conditioning.
Roofs undergo significant expansion and contraction as they heat and cool throughout the
day. Heat absorbed by the roof can also accelerate degradation by ultraviolet rays and
water. A reflective roof can reduce the amount of thermal shock that occurs on the roof
surface 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 as
thermal insulators get eroded as the pores get blocked over time. Moreover, these
products have to be installed at places where there is no load on the materials, e.g., false
ceiling. 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 carried
out 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 the
heat flow and be non-porous, strong and inflammable.
New product
Recently, 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 has
been developed after painstaking research. The trials were carried out in Morvi, Gujarat,
where the temperature in summer often goes above 45 degrees centigrade. During the
trials, the following facts emerged: More than 70 per cent of heat enters the building
through 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 up
to 65 Deg. C in summer.
The conclusions were based on temperatures of the slab, walls and the windows taken
during various times during the day and night.
After the newly developed tiles were installed, the temperature of the top surface did not
exceed 50 Deg. C. In addition to the tile, the study team also developed a system of
