Monthly Archives: September 2011

How to bring in curved roofs

They have a novelty and feasibility, yet offer eco-benefits, and hence are worthy of greater exploration

Advantage: Minor variations in the profile of the roof curve are generally not visible

What has made the digital cameras so popular? Why do simple cosmetics and body moisturizers sell so well? These questions may elicit many layered answers, but we can realise that logical necessity has not been among the prime reason for their popularity. Cameras being easily available or cosmetics being generally desirable have also contributed to their sales.

Likewise, in architecture too, we cannot reason every popular idea to their ecological benefits or economical budget. Some elevation treatment happens at great cost and effort simply because the owner thinks it makes the building better. Architecture also being an individual expression, we cannot question that owner. But what we can do is to infuse a logical ecological idea with a desirability or novelty, so that the idea becomes popular.

The curve inspiration

Curved roofs are a case in point towards this blending of advantages and attractions. The excitement created by the catenary curved roofs built by Barcelona architect Antonio Gaudi has not yet subsided. The early years of Auroville architecture, where many buildings were designed with curved walls and unusual roof forms, continue to influence the architect community. Curved walls and roofs were only a fantasy till recently, but now a reality, as such are being constructed more than ever. However, many doubts continue about how to achieve a good quality curved roof.

Standard roof casting methods suit flat RCC roofs, while curved roofs pose different challenges, primarily in erecting the centering, which also may cost more. The basic centering could be done with steel plates placed in shifting angle closest to the curvature, and then finished to the desired curve with mud.

Rough curve

Alternatively, brick bats could be used to get the rough curve, to be finished on top with weak mortar of 1:12 mix. Plastering the bottom of roof, with perfect curvature is very difficult, since the mason has no tool to check the levels.

As such, curved roofs are better done with alternative ideas, natural materials and rustic touch which go well without plastering. Minor variations in the profile of the curve are a part of natural materials, and generally are not even visible. Filler slab technology already discussed in this column is among the better options to achieve both the curve and good looks.

Once the formwork is ready, we need to assemble the filler blocks of chosen material along the curve, where we can avoid the ceiling plastering.

The lower ends of the roof, which curve more sharply, pose more challenges for handling and demand adequate labour safety measures. We can also profile the curve such that casting it may not be a danger.

We all know that an eco-friendly idea cannot survive by itself, if it’s not an attractive and easily do-able idea as well, however great the concept may be. Curiously, curved roofs have a novelty and feasibility, yet offer eco-benefits, hence are worthy of greater exploration and application.

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.

‘Eureka!’ came too late

Good construction ideas sometimes fail to reach out to the people who need them.

In designing, a better idea is always round the corner

Some of the most innovative and improvised ideas in the construction industry are possibly known to the least number of people! Among the best kept secrets, there lies some solution to our year-long problem. When thousands of architects and engineers work on a wide range of buildings, it is but natural that there would be multitudes of great new ideas. We wish we had known it, but alas, our building is now complete.

With dozens of e-mails expressing the above feeling, it could be worth dedicating one essay in this weekly column just to investigate why ideas fail to reach out to the people who need them.

Before we point a finger at the designers for hiding these non-copyrighted novelties, we need to understand the construction industry. It is based more on individual consultation than on mass instruction. The only occasion when mass awareness happens seem to be during material mega shows, though they may only aim at marketing a few products.

Media can play a major role, yet the reach is limited to niche readership. However much we may design with forethought and leave no stone unturned before commencing construction, the feeling that we missed out on some better option is imminent. It is not because there is a dearth of eco-friendly ideas, but there is a dearth of efforts in disseminating them.

There are numerous practical difficulties in reaching new ideas to all the people. The day we get to know a new idea is an unknown day, by when possibly the idea has been around for years!

Out-of-the-box thinking

Majority of alternative ideas are not covered in our civil or architecture curriculum, and there is no specific academic degree to cover better buildings. As such, our fresh graduates need to learn them afresh in the field. There are a few programmes at NICMAR, GRAMVIDYA, Auroville and INSTRUCT, and many more of them not named here, that attempt specific workshops. Yet no large institutional mechanism exists to explore ideas and options for the construction industry, which is among the largest in terms of turnover, activity and employment generation.

Having said this, it is equally true that there are practitioners who hesitate to publicise for fear of others copying their ideas. However, by limiting our knowledge to our limited circle, clients and customers, we limit our outreach and actually achieve less!

A writer can write about one’s experiences only, as this column does where even the images shared are mainly from a single firm. We welcome our readers to share their ideas, experiences and knowledge, covering cost-effectiveness, eco-friendliness and cultural appropriateness. Individual consultations may lead to mass instructions.

The making of arch panel roofs

Arch panel roofing system helps in dispensing with shuttering, hence making a big difference in time and cost.

Traditionally, most roofs were made up of varied parts such as beams, tiles, stones, mud or thatch, where each was lifted into the desired position in a given sequence. Rarely, except during fixing of domes and vaults, was a full temporary support system called as shuttering or centering. Today, shuttering has become an inseparable part of roof casting, demanding much extra efforts and expenditure, all for a temporary arrangement.

Those who have commissioned a building know how it’s imperative that we stop all other floor works, wait for shuttering people, worry about the perfection in levels and then wait again till it’s all de-shuttered or removed.

Arch panel roofing system helps in dispensing with shuttering, hence makes a big difference in time and cost. Technically, it transfers roof loads the same way as a jack arch roof does, using the curved arch profile. While jack arch work is done in situ , the arch panel is made outside the building, in the yard around.

A long arch profile is made with mud on ground, to be used as the template base for the panels. Small bricks like WPC (Water Proof Course) bricks, cladding bricks or such other ones with good compressive strength and adherence quality are placed flat faced along the curve to achieve the arch shaped panels. The size of the panels would depend upon the blocks we use, which could be between 16 to 18 inch width, 40 to 44 inch length, 4 to 6 inch rise within the curve. The joints get a 6 mm rod in between and are filled with rich mortar min. 1:3 proportion, properly cured with water and carefully stacked.

Simultaneously, required size of RCC beams are precast on the site, with small length of open-ended reinforcement rods on top. All these preparations for beams and panels could be completed while the wall reaches the roof height. After properly curing the wall top, these beams are lifted up and placed across the wall supports to match the length of the panels. Nominal vertical pole support could be provided for the beams, during work in progress. Then the panels are lifted up, placed along the precast beams, joints filled with water-proof mortar, the valley between two panels tied with G.I. wires and levelled with concrete to get the next floor.

While the roof bottom appears rich with beams and curved profiles below, on top it would be like any other flat RCC roof. The panel roof is best suited for any square or rectangular room within 15 ft. width and easy to achieve with minor attention and training.

All normal building usages can be managed and any length of roof achieved by this method. Additionally, the fact that arch panel roof is the among the lowest cost roofs today, ranks it high among eco-friendly roofs, where modern technology and traditional roof concepts merge together.