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Living with RCC roof

RCC performs best during the early years with minimal maintenance cost, but as decades pass by, the roof can be a burden, often with irreparable problems

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During the recent decades, reinforced concrete roof, popularly known as RCC, has possibly evolved as the most common roofing solution in India, relegating traditional solutions like clay tiles, stone slabs, wood planks, brick domes and such others to the back seat in the competition. While increased availability of raw materials, flexibilityof construction and possibility of covering larger spaces has elevated RCC to the top position, whether it is really the best option is still debatable.

RCC performs best during the early years with minimal maintenance cost, but as decades pass by, the roof can be a burden, often with irreparable problems. Being cast as a homogeneous element, spot-specific repairs are not possible or even if possible, they may not work effectively. Preventive maintenance strategy can mitigate the problems to some extent, but people believe that RCC roof needs no attention, hence ignore it only to face problems later on! In case the top surface finish is inadequate, the roof itself gets affected over the decades, with reduced life span. Rehabilitation of concrete structures has emerged today as a major profession, suggesting that all is not well with this wonder material..

Unlike the simple local roofing solutions, the concrete solutions come loaded with many structural theories, methods of preparation and prescribed procedures at site, which are not known to majority of concrete workers. Coupled with inadequate technical instruction and expert supervision, vast majority of concrete roofs being done in India tend to suffer from poor quality and integrity. No wonder, numerous problems surface over RCC roofs, despite the idea itself being an advanced technology.

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Masonry walls or concrete columns?

If you are looking for concrete explanations to choose the right one, read these rationalizations.

Is your house built with pillar construction? If this line sounds familiar, there’s no surprise. Among larger cities today, building the house with concrete pillars and beams is becoming common, just like a multi-storey office building gets built. Have the load bearing walls suddenly lost their capacity? No way, they are as good a system as ever.

In the older areas of any city, houses with two or even three floors are commonly found built with no pillars. Raising the house, wall over the wall and floor over the floor, has been the most common method all over the world. The system is termed ‘load bearing wall system,’ against the ‘column and beam’ method called as ‘frame system.’ Both the systems have their respective advantages and drawbacks, hence require a judicious synthesis, as specific locations demand.

Pillars become inevitable where the soil is very loose, ground is water logged, land is earthquake prone, masonry materials are rare, and light weight construction is desired. A simple criterion for taking a decision can also be to see how our elders built. Irrespective of the site context and precedence, today we see the proliferation of concrete pillars everywhere. Construction costs have gone up, yet the idea has caught on!

The myths…

Among the arguments supporting RCC columns, we hear that more the columns greater the safety against earthquakes. It is not totally true, for structural stability against earthquakes depend upon basic principles such as corner stiffeners, diagonal bracing, height proportions, and horizontal ties. If such issues are not adequately addressed, a framed building is bound to crack or collapse as much as a walled building would.

Another myth is about the reduced cost due to thinner walls, again not fully true for additional costs of the concrete components nullify the masonry savings, where thin walls bring more noise and water seepage as fresh set of problems. Additionally, framed buildings demand alignments to perfection, skills of construction and good junction between materials which are most often missing.

The major two arguments for framed buildings could be the speed of construction and possibility of tall structures. While these two are essentials of multi-storeyed buildings, they are inconsequential for houses, where time saved by columns is negligible considering the time anyway consumed in finishing the house and the advantage of possible height may not be the criteria, for houses are rarely beyond the second floor.

The professionals and the market forces together have misled building owners, erecting RCC columns everywhere irrespective of their real necessity, in the name of durability and strength. Now the time has come where even people simply demand concrete pillars, converted to believe in the myth that they are better. It is high time we realise how RCC frame for houses consume more money, resources and energy, none of which benefit either the building owners or Mother Nature.

It’s all about imaginative placing

May be the act of designing is all about exploring and discovering the hidden potential. Perforated filler roofs fit perfectly into this theory.

The design profession is strange. Often it does not take a project context as a mere fact, but loves to fantasise it. Designers play around the building form and attempt different combinations only to explore the options available, where some good options actually never get built!

Instead of using materials in their basic and simplest form, people try exploring the myriad ways of using them to get a variety of effects from the very same stuff. May be the act of designing is all about exploring and discovering the hidden potential.

Perforated roofs are a perfect fit to the above story line. As the sun moves across the sky, the sun’s rays move across the room, as if the roof acts like a cloak.

Picturesque

This idea started with architects placing coloured waste glass bottles within the roofs, randomly or in a design, creating a picturesque interior. Despite the attraction, issues such as water leakage, breaking of bottles, and shifting during concreting halted the popularity of this idea.

Jaali roofs on steel frames are an extended version and comparable beauty to watch, but appear weak in areas of high security threats.

Replacing steel frame by RCC and embedding the jaali blocks into the slab gives us the normal secure concrete roof, but with the playful small void, each acting like a small pinhole camera.

Adhere well with concrete

The half-cut hollow clay blocks are by far the easiest materials to embed in the roof, though other locally available options could also be employed. Reinforcement rods are placed as per structural design, which should be based on the block sizes. Upon the normal shuttering, hollow blocks are placed with holes up facing skywards with reinforcement rods in between to get the chosen design format.

Structurally, this system acts like a filler slab; hence the blocks adhere very well with concrete, avoiding water seepage possibilities. These blocks can be patterned on any geometry, as long as the steel rods are in position as desired. The normal concreting is preferred more than the ready mix, to ensure the holes are kept clean.

Placing a piece of glass on top ensures rain protection.

Also as skylights

The perforated roofs also act like skylights, though with much lesser direct light.

In hot dry regions where light comes with high glare and sky brightness, it is climatically difficult to have large clear glass skylights, hence this design idea with small holes becomes a good fit that filters in soft light.

Incidentally, in hot regions such as Rajasthan, even the large window openings are replaced by jaalis of small voids!

The challenge is to increase the daylight factor, without increasing glare and sharp shadows. However, there would be increased indoor heat gain; hence roof bottom ventilation is a necessary provision.

The perforated RCC roof does not become lighter than the normal filler roofs, but visually appears lighter.

Besides the eco and aesthetic benefits, the major attraction for perforated roofs could be that it’s a do-able alternative idea, which demands no extra construction skills.

Conventional or alternative?

With 80 essays under this column, thoughts linger if writing about eco-friendly ideas has sent the wrong message that we need to discard conventional systems.

While discussing eco-friendly and green ideas, there is a trap. We may seek innovative ideas for a new house, not realising that the house we live in is already at its effective best.

The alternative ideas always get greater attention compared to the familiar, which is fair in a society where the routine and known are not reported, filmed, featured or published. However, what is not fair is the attempt to project the familiar and common methods of construction as villains of the green movement.

With 80 essays under ‘Green Sense,’ this thought lingered if writing about eco-friendly ideas has sent a wrong message that we need to discard conventional systems.

Three different comments

This rather long introduction became necessary, following three comments by three different architect friends.

* The first comment wondered why the conventional practice, evolved over a century, gets criticised by innovative ideas that are not even a decade old.

* The second comment was, if these alternative ideas can so drastically reduce greenhouse gas emissions and create a sustainable future, why are they not becoming the mainstream approach.

* The last comment shared an experience that despite all the goodness of the eco-friendly ideas, the cheapest, fastest and easiest construction methods are present-day conventional approaches such as plastered brick walls, flat RCC roofs and painted walls.

Discoveries

Design ideas commonly followed today evolved as a preferred option at one time, hence have their own justification. Majority of them belong to mainstream construction practices, enjoying huge popularity and acceptance.

Incidentally, when introduced first, cement, steel, glass, paint, air conditioning and such others were touted as great discoveries, which of course they were, but today the same ideas get criticised as non-sustainable energy guzzlers.

As such, we need to realise that any kind of classification and de-meaning the other leads to nowhere. Every option available is a matter of fact, where the fact to be considered could be cost, culture, climate or construction feasibility.

Following the routine

The alternative ideas do not attempt to compete with the mainstream, hoping to dislodge them some day. Incidentally, most people find following the routine as the easiest and most comfortable, hence the conventional practice will always be the market leader.

What could be called as the alternative offers more choices to people, so that the construction industry could get more judicious. In case the alternative idea of today becomes popular tomorrow, it will then be called as a conventional idea!

In the final analysis, words such as mainstream, alternative, conventional, and sustainable do not mean much to people, who like to have a big basket of design ideas to pick from. At the given time of deciding, whatever appeals to them as the most user-friendly gets built. If people are more exposed to design implications and material effects, one may hope that their choices could be both user-friendly and eco-friendly. Green Sense aims at such a considered decision making.

Flat is fine on the roof

It was as if the century-long search for a perfect roof ended when flat RCC was discovered.

With both architecture and civil engineering stretching into newer frontiers, a dozen types of roof forms could be possible today, yet the flat RCC roof has won over India. From Shillong to Srinagar, Dwaraka to Rameshwaram, majority of roofs being cast are such concrete slabs. It is as if the century-long search for a perfect roof ended when flat RCC was discovered, which is partly true!

The traditional sloping roofs did not permit new additions, unless one removed it completely and then added upper floors. There was no option of terrace use anyway. Most houses of the past were not adequately fire proof, considering the easy combustibility of natural materials.

Geometrically controlled roofs such as sloping and curved ones could not cover any shape of a room, but dictated a proportion between length and width; or between roof height and wall heights. Sloping roofs needed to be well fixed to avoid their slippage which is among the common cause of failure. Against many such imperatives, flat roofs were always an attraction. It is not that there were no flat roofs in history, but that they were far less prevalent. They were traditionally done in low rainfall areas and hot dry climate, but their popularity was restricted to such vernacular practices only.

Being built with locally available materials, the room sizes were restricted, and mostly suffered from water seepage and caving of roofs after decades of existence. Gradually, as the advantages of flat roofs were discovered, people living in heavy rainfall areas also attempted flat roofs, Madras terrace being a good example.

In many ways, flat RCC roof has revolutionised Indian construction, hitherto dominated by regional variations and local practices. Structural issues such as deflection or the sagging of the slab could be arrested by designing the steel reinforcement accordingly. As such, much larger spaces are today covered than ever.

Utilitarian

It is the flat roof that made rainwater collection possible and effective, even though people living in sloping roofed houses also had tried to collect rainwater through gutters, but with much less collection. Flat roofs lend themselves for a variety of utilitarian activities, so they double up as a small gathering space; roof garden; material dumping place; place to sleep at night or play area for children. Comparatively, they are far easier to cast, being just a horizontal surface, which could be placed on any irregular plan form.

From an ecological perspective, though heat gain is an associated problem, it could be reduced with many alternative methods such as mud phaska layer, brick bat coba, flat burnt brick tiles or roof mortar painted with white paint or lime coat. RCC roofs have high embodied energy and excessive use of RCC damages nature more than many other options. However, considering the ease of maintenance and affordable costs, they are the most popular roof form today.

The forgotten roofs

This system with wooden cross beams does not need centering, allows faster construction and demands less structural skills. 

Can the way generations before us lived for thousands of years be continued today? If some ideas are extinct today, where did they err? Do they have any future at all, or are they better forgotten? Before we go into this debate, let us look at some of the past practices, now less used and on the decline.

If we walk into any typical village, we routinely see houses where the roofs have closely placed wooden beams, often as close as six inches, which have wooden twigs and short branches above them, running in the opposite direction. There could be some dried leaves visible above them, or it could directly be a layer of mud mix. These houses were built with minimal cost, often termed as kutcha and face fire, rodents and such other problems. Alternatively the wooden cross beams could be topped with a piece of burnt flat clay tile. The tile layer gets a mud layer on top with the final floor finish.

Where ample quantity of construction timber is available, we see wooden cross beams at a wider span, say 1 to 2 ft. wide, which support a layer of min. 1.5 inch thick wood plank on top. In most houses, a thin layer of lime concrete could be seen above this, finally finished with red oxide floor. Mud flooring mix could also be used above the mud planks, in low termite prone areas. This wood beam concept comes with different variations, among the popular ones in many Sates being stone slabs replacing wood planks as the base of floor material. Any good local stone could be used for this purpose, though stone slabs have defect lines depending upon their material composition, hence are liable for cracking.

This system with wooden cross beams does not need centering, allows a faster construction and demands less of structural skills. These roofs are local by nature, hence more eco-friendly and sustainable. On the negative side, we may list the difficulties of electrification, and feasibility of base materials such as wood or cuddapah. However, this system could be revised by replacing wooden cross beams with steel joists and the sub-floor base by flat hollow clay hourdi blocks or granite or RCC slab precast at site.

When a construction idea popular for centuries loses out, mostly it happens for no mistake of the idea. People may make a mistake in implementing a construction element, but that does not mean the idea is wrong and needs to be discarded. However, if seemingly better ideas get introduced, the earlier systems become less desirable. Most traditional vernacular roofing ideas are still valid and in case newer, better ideas are not possible in the given site, can be replicated.

To that extent, it is advisable to do research on our past architecture and ready them for modern applications.

Vanishing skills

Why are seemingly unsustainable practices of today more dominating, while the eco-friendly practices of yesterday are forgotten? 

Those who have commissioned a building project possess a special knowledge that the others do not. Simply stated, it is the awareness that getting a building, specially a house built, is easier said than done! More importantly, it is learning about the need to simplify every construction procedure, of course without compromising on design or quality. To this end, roof being among the more complex part of building construction, has seen more research than other component parts, with much that could be written about roofs.

Yet, nearly everywhere we see flat RCC plastered and painted roof slabs today. Quite naturally, there are reader enquiries wondering why discuss domes or vaults and who can build them after all! Every alternative idea has limitations in terms of quantity or popularity, lest it too would have been the mainstream activity. Some of the roof alternatives we are discussing are actually not mere alternatives, but time-tested ideas practised for thousands of years.

The only challenge then is to simply revive them. May be, as much as discussing the idea, we also need to discuss why these proven ideas have lost their edge, to understand why seemingly unsustainable practices of today are dominating, while the eco-friendly practices of yesterday are forgotten.

Among the major issues that we are confronting today is lowering skill levels. It is not so much because people are no more capable, but because people are not being employed for specific tasks, hence lose out on the practice so essentially required in construction industry. We the professionals then blame the construction scene saying we no more get good carpenters! If prefabricated windows replace wooden windows; if steel shuttering replaces wood plank shuttering; if ready-made kitchens replace hand-made kitchens; and then if carpenters cannot get a full month earning, who is to be blamed?

With reduced employment opportunities, the younger generations ignore specific tasks such as carpentry. In masonry category, building arches and domes are among the major casualties, but more dangerously, nowadays we keep hearing about bad brick walls because the young masons do not know how to build a wall. If these rumours become a reality someday, that will be the end of good buildings in Indian cities.

Implications

What are the implications of this impending doom? Quality assurance by factory manufacturing overrides quality by human skill perfection. Manufacturing, despite benefits including economics, speed, delivery and good finish, leads to many traps such as energy consumption, low recyclability, and unequal wealth distribution. While a certain degree of manufacturing is essential towards a basic building, construction industry mainly relying upon produced, branded, transported and site supplied chain of materials could be disastrous.

It may not lead to a sustainable future with the construction sector already adding more than one-third of greenhouse gas emissions, and specifically in Indian contexts, where we need to employ and feed millions of people. As such, all alternative and eco-friendly ideas need to be welcomed today.

Go for curved roofs

A look at the multiple benefits 

Do you feel flat roofs are too common, making the building look like a box? Often, they also have been hot boxes, leaking during rains. Sloping RCC roofs are fine, but we need to finish with tiles on top, creating a double roof, unnecessarily spending extra money. Since the sloping roof rises along the length, the longer the room, higher goes the roof height. There are many houses with an externally impressive sloping roof but internally appearing so much out of scale that the architects are forced to suggest a loft up there, often only to make the height bearable.

Given this scenario, roofs with one-way curve, like the segment of a circle, help in many ways. Even if we start at the lowest end at nine ft., we can restrict the height at the higher end to reasonable limits by gently curving up and then going generally flat where the roof meets the wall. This solution where we can get a roof seemingly curved in front and flat behind is mainly for large spans, so all smaller rooms can anyway get fully curved looks.

Orientation matters

Besides modulating the height, there are also passive cooling benefits. The amount of heat getting conducted into the building depends upon the angle of sun rays where the direct rays conduct more heat and angular sun rays tend to reflect back to the sky, hence have lesser conduction. Solar heat is the strongest from 10 a.m. to 3 p.m., being cooler before and after these hours, thanks to the low sun position. Depending upon the orientation of the sloping roofs, facing north or west, they can be designed to receive varied degrees of heat, but often the design context may not permit us to slope the roofs anyway we want.

Maximum heat transmission happens in flat roofs which get direct rays for the longest hours compared to the other forms.

It’s here that the curved roofs score over the others, getting direct sun rays for the least hours. Only a small part of the curve at any given time would be subjected to direct solar light and heat, other gradually curving surfaces receiving the light at oblique angles, hence receive less heat, leading to differences between outdoor and indoor surface temperatures.

Tiled looks

Visibility from the road side is among the reasons people prefer to have sloping roofs, with a desire for tiled looks. While we get to see the tiles from afar, as we come closer to enter the gates of the building, we see the lowest edge of slope as a straight line only, disappointing both the owners and the visitors.

With the roof curving, the curved profile is visible wherever we are, unless we stand under it. This contribution to aesthetics compliments other design criteria, in favour of choosing curved roofs.

Exciting options with filler roofs

Filler roofs are designed using the same principles as RCC, except for replacing part of the concrete with some alternative material. 

Last week belonged to queries about filler roofs, following the preceding essay introducing the idea. No wonder there were so many questions about it, considering it is an exciting solution, though less heard of. While the regular RCC is widespread even in remote villages, it is surprising that filler roofs are hardly known around and have minimal visibility.

By the early 1980s, many roofs were cast with filler material in Kerala and later in Bangalore too. With nearly 30 years behind them, their durability has been repeatedly proven. Incidentally, when a commoner wonders if the roof is strong enough, what actually he enquires about is whether the roof will structurally perform well with load transfer, tension, compression, deflection and such technical matters. Since filler roofs are designed using the same principles as normal RCC, except for replacing part of the concrete by some alternative material, worries about strength can go unquestioned. It is the designing for tension load, hence the spacing of steel reinforcement that would differ as per the sizes of filler material.

No new problem

Behaviourally, the slab acts like any other slab, and as such does not pose any new problem not seen in regular RCC roof — be it with possibilities of water seepage or cracks! In either case, normal RCC or filler, such issues need to be attended to, should they appear unfortunately. Quality of construction at site is a pre-condition which can affect both the mainstream and the alternative practices, and as such should not be used only to degrade the alternative!

Availability of the hollow clay filler blocks could be an issue, to be explored by the potential user, but any local clay roof tile supplier could be of help. Alternatively, a variety of locally available materials could be inserted as filler, including stabilised sun dried mud bricks. When we place glass bottles or perforated jali blocks, we get skylight effect.

Cement blocks have already been experimented with, which then could be plastered and concealed. There are many filler roofs done with mud pots or bowls as filler material, where we get the looks of an artistic ceiling, at a lower cost.

While concreting, the filler blocks may move due to labour movement, which demands careful on site handling. Depending upon the room size, there could be savings in the steel cost; however the cost of block and increased labour would ensure our savings are spent! In large span roofs, where it is desired to avoid the beams, one may design a thicker slab, then introduce filler concept to save on concrete.

When the whole roof gets cast as clay filler slab, it’s possible that some family member may not like the red look at the bottom of the roof. Such people have the choice of getting the ceiling painted white, giving a designer false ceiling appearance, thanks to the fluted profile of the block!

Concrete roof rules

The basic skill to cast it has percolated down to remote villages too, however over designed or wrongly mixed it all could be.

Look around today. Everywhere everyone is in a hurry to cast RCC concrete roofs. However, if this line is taken as a compliment for RCC roof, sorry it is not. It is a statement of concern, about a versatile material being indiscriminately used, including in areas such as sitouts where concrete roof is just not necessary.

Let us accept the fact that reinforced cement concrete roof, commonly called RCC or concrete roof, has been a great discovery. It has solved innumerable problems including providing security and opened up design options such as shell roofs which were never dreamt before. Though only qualified structural engineers know exactly how to optimally design these roofs, the basic knowledge and skill levels required to cast a roof has percolated down even to the remotest of villages, however overdesigned or wrongly mixed it all could be. No wonder, small bus shelters, not so permanent milk booths, park pavilions, storage sheds or village houses, which in the past were roofed with sheets or tiles, today get RCC roof. Projects tendered by the government compound this overdoing, by insisting upon concrete roof everywhere.

Steel and cement are among the production industries that consume humongous resources; hence have very high embodied energy. Of course, today they top the list of materials for being most popular and widely used, as such are seemingly irreplaceable.

Additional burden too

Most of us forget the additional burden of the temporary support called centering or shuttering, which after some use becomes a total waste. Among all the needs of water for mixing and curing, it is the roof which singularly consumes the largest quantity per square feet. Segregating the steel reinforcement and concrete from the discarded old buildings or irreparable cracked roofs is hugely time- and resource-consuming. Even if we use cutting machines and succeed in this segregation, it is impossible to reuse old concrete but for some land fill.

Unlike any other traditional roof, a concrete roof once cast can never be returned to its original ingredients, and will continue to burden the earth for a long time to come. Till recently, concrete roofs were labour intensive, hence provided the much-needed labour opportunities.

Now-a-days, manual casting is being replaced by Ready Mix Concrete in large cities, further reducing on people benefits. Considering concrete is far from being eco-friendly, the way it has relegated all earlier roof options to the back seat is both amazing and alarming.

Having said this, let us realise the solution does not lie in discarding concrete, but in using it judiciously. Also, there are numerous methods such as arch panel roof, filler slabs and ferrocement technology which basically employ steel and cement, but create alternative options for construction.

In these days of rising price of RCC roofs, it is time to explore such alternatives, for both ecological and economical reasons.