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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.

Jack arch roofing

This is traditionally styled where the arches are formed in the roof itself supported by the centering. 

Between the flooring and the roofing, what is more important? Undoubtedly, it is the roofing. Yet, curiously, we find thousands of patterns and products for the flooring backed up by huge advertisement campaigns, while there is hardly a whisper about the roof, but for the builder informing about the day of roof casting! It could be linked to the fact that most often we are looking down, hence tend to ignore looking up to the roof.

If we start looking up, we would realise that arched roofs are among the more attractive ones, presenting a designer or false ceiling appearance. The more traditional ones are called jack arches where the arches are formed in the roof itself supported by the centering, while the recent researched type is arch panel roof, where the arches are made on ground to be lifted up and placed.

Across the walls, wooden or steel cross beams are placed at not more than 3 ft. spacing with the short gap in between formed into a shallow arch form, to work as the temporary roof base. Good quality local bricks, preferably the thinner type, are placed on this base in a curved arch profile. The joints are finished with rich mortar. If the upper floor is to be used, it could be levelled or water proofed to be left as the final roof. In case thin hollow clay blocks, also called as water proof course tiles (WPC tiles) are used, additional passive cooling can also be achieved, besides ensuring the roof within the normal thickness. No structural steel reinforcement is required within the arches, for they naturally transfer loads along their curvature. Only nominal 6 mm rods are placed within the joints to hold the blocks together.

Length, an advantage

Among the advantages of jack arch roofing is unlimited length. Once the width of the room is limited, say within 12 to 15 t., which can be connected by wood beam or steel girder, the length of the room can be adjusted. There is no longitudinal member at all, hence this possibility. If all the material components such as cross beams and tiles are ready, the making of the roof is fast with no extra time demanded for placing reinforcement steel or extensive curing.

Masons have to take good care to achieve proper curve in each of the arches, so keeping a template piece is advised. During casting, steel centering could be used, but the top arch surface has to be in mud or lean mortar to achieve the curve and also to ensure their easy removal after casting the roof. Since the individual arches are resting on cross beams, centering support is needed only for the cross beams. Electric conduits can be run as normal, with hole punctured in the tiles to fit roof boxes and provide the standard wall elbows.

Why this state?

Even though jack arch roofs are economical and eco-friendly, their application has reduced. The skill levels for handling the roof have also reduced. If we desire, they can be revived.

Many solutions for the roof

The new roofing technology is more advanced, but at some places the old practices are appropriate, and we need to blend the two.

Let us recollect our visits to villages and small towns, check out the kind of roofs we might have seen and compare them with the practice today. The idea of a monolith single material concrete roof we now know, is of recent origin. Traditionally, many building materials were put together to create the roof which then made sense because a range of local resources could be mobilised to get the best of roofing solutions. Clay plus wood for Mangalore tiles roof, steel plus bricks for Madras terrace, wood plus cudappah slab for stone roof, wooden beams plus planks for intermediate ceiling and such others that exist even today in our century-old houses and buildings amply prove their advantage, affordability and versatility.

Simplifying the roof

If we need to roof a room 18′ long and we find it difficult, what’s the common sense solution? We may place a wooden cross beam between the supports at every 3′, so effectively we need to roof six spans of 3′ each, which is much simpler. If only small stone slabs are available as roofing material, this could be reduced to 2′ each, by placing more of the cross beams. Of course the width of the room has to be limited to the available length of cross beams, say within 12′, which is fine with majority of residential activities. The space in between the beams or the narrowed span has to be now filled, using any of locally available appropriate materials.

In case the width is more, the simple cross beam has to be made stronger by triangular truss-like formations, provided with a central pillar support or wooden members replaced by steel sections. For buildings demanding larger indoor spaces, more advanced solutions need to be applied.

Technically, there is nothing wrong in this approach. However, advancing time discovered newer modes of roofing, based primarily on reinforced concrete and structural steel, as necessitated by the specifications of different projects.

Standards and codes

During the colonial and post-independence era, the building construction industry got formalised with standards and codes written, where certain practices were retained while the others were discouraged. Formal education, idea of textbooks and degree-based professionalism further damaged the image of local practices. Just like in medicine or folk wisdom, many effective solutions got sidelined, and today hundreds of time-tested design ideas get neither support nor promotion by the building industry.

If this narration sounds familiar, where the march of time leads to the new replacing the old, yes, it is a familiar story. If only the ‘new alone’ could have been our saviour, if all the modern ideas were to be ecologically sustainable and if the technical solutions of today are affordable by all – may be, we would not have sought any other option but modernity and high technology. The new roofing technology is more advanced, but at places the old practices are appropriate; as such we need to find ways of blending the past and present.