JACK ARCH
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.
