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Designing a chajja


It can do as much harm as good, if not well designed.

The idea of seeking shade from sunlight is as ancient as the human civilisation itself and this statement may elevate the respect we should give to sunshades above our windows. However, we have reduced it to a ubiquitous flat RCC slab, often used everywhere without any reason.

The word commonly known today as ‘chajja’ is the projected element just above the window, which shades the opening, stops rain from entering the room and reduces sky glare while looking out of the room.

Ideally, each window needs to have specifically designed element based on the orientation, sun directions, rain patterns, monsoon wind, sun path and such others, besides the activities inside the room.

However, it is of common practice today simply to cast a flat RCC slab as an extension of the RCC lintel beam, which can do as much harm as good, if not well designed. Between buildings with a very narrow gap, sunshades will block the little light and air we can get, hence should not be provided. The buildings shade each other.

If the chajja is to mainly serve the looks and elevations, the ordinary flat projection will adversely affect. In a north facing windows which get minimal rain and harsh light, chajjas can be generally avoided, but for aesthetic reasons. So, fixing a flat slab is not a solution in every context.

Imagine the alternative, more attractive windows like arched windows, which is liked by many people for the character it gives to the building. In typical cases, it is avoided, because not all masons can build it and equally well because it cannot have a chajja!

In historic structures, a small cornice band would appear above the void, acting as a drip mould – directing the water flowing down the surface away from the window. Today, such decorative bands are out of practice. Negotiating the curve with a vaulted RCC is too costly due to centring and finishing it; Mangalore tiled chajja is ruled out in this profile and there can be no standardised chajja considering that curvature may vary between two windows. Unlike a normal window, arched ones definitely need protection from both top, called vertical shadow, and from sides, called the horizontal shadow.

One option is to place the chajja also in a curved profile, with the projection anchored to the wall itself. Inverted T sections can be grouted just above the arch following the same curvature which can take flat clay hourdi tiles, stone slabs or even lightweight in situ cast RCC slabs. Only the joints between the top materials need to be waterproofed.

Designing the right shade

Slabs come in many shades to protect your building from intense heat and rain.

02bgp-greensensGMG5BTPAL3Ask anyone if he or she prefers sunlight or shade – the answer is predictable with no failed guess! Shade is what all animals need, including humans.

Early architecture in the tropical zones of India had overarching criteria in creating shade and it was more critical than any other criteria. Incidentally, it continues to be an important consideration even today in eco-friendly designs.

Creating shade for the whole wall is among the early knowledge people picked up while designing for the climate. Initially achieved through simple ideas such as projected roofs, closely placed dense housing, deep verandahs, planting trees and such others, slowly led to windows set in thick walls, projected jharokhas and roof stone extensions. Traditionally, designs had deep roof eaves such that sunlight and rain would not penetrate deep into verandahs, porches, porticos, entrance mukha mantapas, balconies and walls facing south and west.

A formal study of buildings by experts led to a variety of options to shade specifically windows, leaving the wall open to sunlight. In normal buildings, it is common to see the horizontal chajjas or sunshades, done today mainly with RCC. Many windows also have vertical projections on both sides called fins, or it could be projections all around with a box chajja. RCC has emerged as the most prevalent material for all these, though it is not among the best options.

Among the less studied category are vertical drop slabs useful to stop both the sun and rain. They also protect our eyes from direct sunlight even when we are sitting outdoors in semi-open spaces such as balconies or entrances. Often, the upper floor common passages along the outer edges of commercial buildings would have them so the lower floors will not get direct rains. Most city homes have car porches with a room on the first floor so the clear height of the car porch may reach up to 13 feet. If the house faces south-west or direct west, evening sunlight would reach deep into the porch, heating up the car due to light and wetting it due to rains.

These vertical drops cannot be done with simple masonry, while complete concrete solutions could be costly. Traditional buildings could afford to have wooden planks in this area. Very often they are done with chicken mesh plastered on both sides, also called as Ferro-cement slabs, but they tend to crack under the strong sun over the years. Some designer buildings exhibit well placed horizontal louvres, which demand good detailing and execution.

Simple solution

A simple solution lies in using any stone slab, sheet metal, large clay tiles or matted material that can withstand direct sun and rain. They could be fixed with steel channel sections hung from roof slabs by inserting the slabs within the sides or grooves of the section.

If well designed and detailed to match the elevation of the building, the vertical drop slabs can be an element of attraction, rather being an ugly but unavoidable addition.

For thermal comfort

Knowing daylight and shadow patterns round the year is helpful, and common sense observation can be the starting point for understanding light and shade balance in buildings.

Often we see design ideas going through a paradigm shift, nearly to the opposite ends. To realise this phenomena, look at this — from the past practice of building for shade inside the jan5house and outside on the walls, today we are seeing buildings washed with light everywhere. Accordingly, windows on the walls have become larger, external walls are exposed to direct sunlight and skylights have been introduced.

While the theory of light is desirable, the resultant heat built-up is a nuisance no one can live with, hence the need for ideas to shade the building. From an eco-friendly perspective, the more shaded the building, the more cool would be the inside space. In case of air-conditioned structures, this would reduce energy needs; and if not, we achieve more effective passive cooling.

Emergence of chajjas

During the early years of modern architecture in India, simple projected chajjas were introduced. Most people think they are mainly for rain, which is not true. As shading devices, though without specific considerations of direction, depth of projection and materiality, they continue to be popular in India.

Thinking architects like Le Corbusier experimented with alternative forms, and came out with specially inclined concrete walls outside the window, often called as Brise Soleil. Much before him, the Golconda building at Pondicherry had a series of horizontal concrete fins. Such external skins placed closely to the walls allow wind movement and let in diffused light from the bright tropical sun but prevent direct solar radiation into indoor spaces.

Indian traditional designs did not use an external skin, but provided deep overhangs like at Fatehpur Sikri or built external walls as perforated jaalis to reduce heat built-up as found in Jaisalmer. Or positioned wooden louver-based features as walls as seen in the Padmanabhapuram Palace. Of course these are among the best examples we get, with thousands of variations with lesser effect commonly found all over our country.

Solar charts

While all the above measures are valid and much needed, our data base for ensuring shade has drastically improved over the years. For every region now there are solar charts – specifically locating the sun in technical terms like altitude and azimuth for any given minute of the year.

It is possible today to calculate the exact pattern of shade for any given time using manual formulae or computer simulated software driven programmes. These measures assist in designing the shading device to derive increased shade in summer and increased sunlight penetration in winter. India being in the southern hemisphere with high summer sun and low winter sun is a difficult place to design for, considering our vast geographical extent and regional diversities.

No single solution can serve year-round needs; hence we need to think judiciously to derive maximum benefits across the seasons. While computer software can help, common sense observation and following the right kind of precedence can be the starting point towards a building where light and shade are balanced.

Tackling sunlight

Eco-friendly architecture and green buildings depend largely on elevation design, and specifically window design.

22bgIt is a paradox. Without consumption of sunlight we cannot live; equally well, without protection from sunlight we cannot live. In a modern context, this apparent contradiction needs to be resolved by the design of windows, hence eco-friendly architecture and green buildings depend largely upon the elevation design in general, also called as façade treatment, and specifically window design.

Three parameters

If we search for the essentials of architecture as shelter making, we end with up three parameters. Shelter from heavy rain, protection from cold wind and shade from harsh sunlight. The first is served by the roof; the second by the walls; and the last by both roof and walls. Of course it would be a dark box if only roof and walls exist. As such, to let the required air and light, windows were installed by the early human settlers. They were small, being built into the building volume, hence naturally protected. Contrastingly, today windows are large, placed at the open edge of the wall, exposed to vagaries of nature, demanding adequate measures not to let rain in and stop direct sun into the building.

The chajja

Traditionally, most regions of India did not have the projection, nowadays called as concrete chajja. The sloping roof overhang was so deep, it would cover up the wall and window opening. Alternately, there would be a wooden bracket supporting the sloping sunshade over the windows. In case of flat roofs in hot arid regions, small stone slabs or sometimes an ornate window design as a box can be seen. The formal concrete slab projection as chajja appears to be a post-independence phenomena, further popularised by PWD norms. Irrespective of cardinal directions, sun movement patterns, degree of shading required, type of building or any such criteria, we have been adding this concrete slab over the window everywhere. Most often, we do not know how effective this shading device has been.

Incidentally, in dense urban housing areas, the chajja may also do more harm than benefit. With neighbouring building standing tall, the whole wall of a building can be shaded, ruling out the need of chajja shades. With narrow setbacks between two houses where no direct sunlight reaches the windows, the chajja would further reduce the incoming indirect light, making the houses darker. When a chajja faces the direct sun, the air around it heats up, which trends to enter the house, increasing the interior heat gain. There have been numerous cases where chajja becomes a point of water ingress.

All these above notes are not to negate the need for chajja; they are also needed for stopping rain, add elevation attraction or protect the wall from rain water flow along the surface.

The point is about designing studied and properly reasoned solutions for shading a building, without losing out on indoor light or air. Incidentally, all such climate responsive buildings have also to be attractive and culturally appropriate.

The rough look is cool!

When you get rid of the straight lines, you have to use your imagination to deal with all the curvatures.

Know the basics: Rough-textured walls receive less heat

Have we ever tried to go close up to a tree trunk or a hill-side cliff? We notice the seemingly plain surface has a thousand minute folds. How is the surface of a seemingly smooth rock boulder? Close up, it is rugged and not in one smooth plane. What about fruits, vegetables, timber logs or tender coconut shells? It is the same story everywhere — all non-planar, rough textured, micro-folded and gently curving.

If nature never had a smooth, straight and fine finish, where did we humans get all these ideas for our constructions from? Why are we not trying to learn from and emulate nature?

Village scene

Incidentally, we have followed nature, but mostly during the bygone days. Let us look at any typical Indian village home. This vernacular-style approach used to be rustic and not in perfect plane, being hand- or simple trowel-plastered.

Often there would be natural materials such as stone, timber or bricks left exposed, hence solar passive, also creating a sense of local material and character.

Smooth-plastered walls receive more heat compared to rough-textured ones, since the latter cast micro shades within the wall, thanks to their roughness. If used in the natural state without plastering, brick and stone exhibit such a textured surface that they absorb much lesser heat.

Beauty of curved walls

Gentle curves are part of most objects found in nature, which could be blended with our regular walls to get multiple benefits. We rarely make full use of all the four corners of the room, as such converting one corner into a curved edge does not reduce functionality. Critical areas where storage, furniture, shelves, platforms and such others happen could be left straight, while the movement areas and passages can flow along a curve.

There could be issues like fixing windows, casting curved lintel beams, workmanship, perfect plaster levels and difficulty in using tools. However, if we are able to retain the sense of curve, the job is well done.

In our context, building materials such as stone or brick are rectilinear, hence making the curve using such geometrical blocks needs an expert mason.

Folded walls

Among the much less used variety is the folded wall typology. It was Laurie Baker who discovered that thinner walls with half-brick thickness save money, but need to be folded to gain strength. Incidentally, from an ecological perspective, these folded walls have add-on values!

They create so many external deep-set alcoves that most wall surface is under shade. Not all rooms of a house could be comfortable with folded walls.

In non-residential building types like those at Hosa Jeevan Daari at Melukote, such a wall plan internally creates storage niches, with an overall elevation that looks different and attractive.

Windows now set within the alcoves are well sheltered from rain, with no additional chajja protection needed. One approach can reap many benefits.

How many RCC lofts do we need?

A ground or lower-level shelf can do the same function at a lower cost

Being practical: Go for smart storage spaces

There are few things we accept in a new house construction without blinking our eyes. The RCC lofts seen at 7′ level, also called the lintel level, is surely one among them.

It all started following the introduction of RCC during the last century. Lofts are projected from a beam in the wall, which also double up as the lintel beam above the window. Commonly, this lintel is run all along the wall, forming a continuous lintel. The idea became popular, for one could have a loft slab anywhere since the lintel beam is all around. So, the triad of RCC at 7′ level formed by flat chajja, lintel and loft came to stay, irrespective of how much of this RCC is critically necessary, apart from the time lost during the casting.

Earlier, all that we could provide was an occasional wood plank projected from the wall with two angular wooden brackets supporting it. As such, the RCC lofts have become so popular that no room goes without one or two of them.

Friend or burden?

Knowing our tendencies towards piling up junk, it is no surprise that lofts have become our dear friends. Yet, occasionally, we better question how many lofts we need. How often do we store heavy items which need a RCC slab? If we continue to collect over the decades, how many more lofts we may need? Even if we can cast them all today, how many of us can lift such weights up to the 7′ height?

Would a ground or lower-level shelf perform better than these high lofts? What about the dust collected and cockroaches housed? Between eliminating junk and eliminating RCC lofts, which option should we choose?

RCC lofts are a rigid addition within the walls, which force kitchen cabinets or wardrobes to fit into their levels. With a variety of options available for such interiors, often the lofts become an obstacle.

Storing without costing

It is curious to realise that even without a RCC slab atop, the top level of any wardrobe can be used for storage, hence act as a loft!

The cost of slab can be saved, that could partly pay for the wardrobe cost! The kitchen lofts are less accessible while standing in front of the kitchen platform; as such, lower-level cabinets are more comfortable any day.

Separate store rooms are possible if space and budget permit. If exclusive RCC slabs are desirable, the best location would be above toilets or passages, simply supported on side walls, with a minimum clear height of two ft.

Going green starts with minimising and eliminating unwanted consumption of construction materials. All of RCC that goes waste at lintel level could be a testing place to check out this principle.

Does your sunshade play its role?

Chajjas’ come in attractive types now but their placement is crucial for giving shade or letting in light and air

Differing tastes: RCC slab projection on buildings started during the colonial times but many buildings do without them

In the history of Indian architecture, chajjas have a curious place. You may not even recollect what part of building I am writing about now or what is so curious about it.

Well, if we walk around historic towns like Srirangam or Sringeri or Thrissur, chajjas are conspicuous not by their design, but by their total absence. Up north, even in the desert dwellings near Jodhpur, traditionally there were no major chajjas.

Sunshades, more commonly called as chajjas, are the little horizontal projections along the external wall, just above the windows to reduce sunshine and raindrops falling on the opening.

Local styles

The clay-tiled sloping roofs of south India normally extend deep beyond all walls, windows and verandahs providing climatic protection, as such never had a typical chajja.

In north India, often there would be a small beading-like projection, sometimes a moulding to drip the water drop or a small stone slab above the opening. Only in important civic, religious or royal buildings, one could see a deep sloping projection supported by ornate brackets placed at an angle between the wall and the projection.

As such, the RCC slab projection called as chajja started during the colonial times, when buildings tended to be like a box, with flat roof, inviting vagaries of weather all around. In such cases, sunshades are necessary in our region for climatic protection, though we tend to see many multi-storeyed buildings without chajjas.

The flat chajjas are cheaper, but jet out of the walls like the rim of a cricket hat, and make the building look ordinary. They also tend to look discoloured after a few showers.

Builders have tried sloping ones, which demand deeper beams, tiles on top and painted finish at bottom — all leading to more RCC and cost. When chajjas happen between two houses within the narrow space there created by the bye-law setbacks, instead of protecting, the chajja can cut off the possible light and air into our own houses. There often are directions from where we get no major sun or rain, making the chajjas there totally futile.

Interestingly, if heavy rain lashes and the window is left open, water anyway gets in despite the chajja!

Gaining popularity

All the analysis above is not to negate chajjas, but to ensure a better understanding of how and where to use them. In the recent years in Bangalore, Mangalore tile chajjas have gained popularity. They are supported by fabricated mild steel frame and can be fixed into the wall only where we need, just before completing the building. Often, we have come across owners who wanted to check out which windows need them for a year and then fix them accordingly. With sloping clay tile top, leakage is not an issue and the pricing is also reasonable. Such tiled chajjas compliment the green aesthetics of the building.

Always go for short and concealed lintels

Every era brings in a new wave of thinking and, with age, a new architecture is born. Concepts such as lintels and their design, for example.

How often do we observe the house where our parents lived? What kind of lintel do we see there? By any chance, do we live in a house built 30 or 40 years ago? When we return to such old houses, we notice, there often was no monolith lintel beam concept.

The window frame would be placed in position, then the bricks would be carefully placed above the frame with equal projection on both sides, to start the remaining part of the wall. Here the bricks tightly joined between the void, would act like horizontal means of load transfer, while a smaller part of the weight would be taken care of by the window frame. This concept can be further developed into what is called as flat arch lintels, which unfortunately is not very popular today. Instead of this bricks base layer, there could be a wood piece in some cases. During later years, the trend of casting a RCC lintel after the frame placement also started.

However, there never were anything like lintel member running all along the house, yet these buildings have been with us for centuries. Having said this, let us also agree there are many advantages of continuous RCC lintels. The only plea here is to think if such lintels are judiciously required or not.

Required everywhere

Lintels are needed for sure above any and every opening, be it a door, window or wall niche. When we provide them only above such openings, it is called as cut lintel system. They are short in length with adequate bearing on the wall at their ends, and can be managed with minimum reinforcement. To save time, often they are cast on ground, to be lifted up once the walls are ready. Such pre-cast RCC units also save on centering and concreting labour. Cut lintels may not offer any quake resistance, and as such need to be evaluated against all other criteria.

Another popular approach is to merge the lintel with the wall material. Exposed brick walls may look nice with the plastered RCC band, yet they can also be built without the lintel being visible. The outer edge would have a brick, with the thin lintel behind. If it is a hollow clay block, the concrete can be filled within the hollow of the block, creating beam-like support. There have been experiments where hollow blocks have been cast into a monolith beam by inserting reinforcement bars into them. Such walls, with the chajja or the sunshade above the window, tend to look very neat with the aesthetics of single material.