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.
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.
Jaali skylight can replace clear or translucent glass, thereby reducing the quantity of light and controlling the daylight factor.
Delightful: When sunlight filters in…
Have we ever walked under temporary roofs done with interwoven coconut tree leaves? In rural areas they are a common sight, especially during weddings, festivals, public congregations and such others.
Sun rays filtering through the voids of the leaves, moving across the hall as the sun moves in the sky, and creating a playful interior is a delightful experience to bask under. If designing can source inspiration from nature, such enclosures created with natural materials can also be an inspiration.
There are a variety of jaali blocks, bricks with hollow voids, available in the market. They are placed within mild steel framework, fabricated to the size required, with mortar packing in the joints from above. Depending upon the area to be covered, the structural design of M.S. frame may get cross beams and edge beams, but the top of all purlin-like horizontal members should be at the same level to take the blocks. The steel and block junction needs to be water-proofed, to stop water penetration there which may rust the members.
In case minimum light is desired, half of hollow clay block can be used, though it is not a light weight solution. The regular clay jaali blocks are only 2 to 3 inches thick, making their use the most ideal. Inverted T sections are the best, though angles and flats can also be used in various combinations. The top surface can be topped with glass, where the fabrication can be done to a gentle slope, to avoid rainwater falling inside.
Perforated roofs can give a miraculous touch to the internal skylights and courtyard roofs. While light gets in, it can happen so only through the voids, hence the interiors get a soft touch.
Especially where a single piece of glass is not desirable due to quantity of light, jaali skylight can replace clear or even translucent glass, thereby reducing the quantity of light and controlling the daylight factor.
In case the block size appears large and feels insecure, additional mild steel guard bar rods can be welded into the roof support, creating the window grill type of fabrication, to increase the sense of security.
The jaali roof has a great advantage in being a light weight solution. In case a rooftop enclosure is desired where weight restriction limits our options, jaali roof is a safe choice. If rain can be let in, the roof need not be topped with glass, making the overall roof still lighter.
For air, light, rain…
Jaali roof is a slab for all practical purposes, but can let in all the three – air, light and rain! Hence, it is best suited for outdoor purposes, where there is no further upper floor. Being an assemblage of structural steel and blocks, it is not at all cumbersome like the RCC slab. The aesthetics, ease of assembly and maintenance together make the perforated jaali roof a choice for many occasions.
Indoor air movement can be controlled by careful positioning of openings in opposite directions
Right design: A jaaIi wall looks stylish from the outside and provides light and privacy too
Somewhere down the history, thanks to the invention of operable windows with shutters, we have forgotten all about walls with openings in them. These perforated walls, also called as jaalis in our region, can be seen in all Indian temples, Middle Eastern mosques, African huts or Cambodian monasteries. During these days of solid walls, this global use of jaali walls is only a reminder of a forgotten heritage and neglected green sense.
During the days when glass windows were yet undiscovered, masonry wall concept prevailed and the only option for providing openings was within these solid walls. Based upon the local material and climate, varied modes of creating the voids within the walls were explored, them playing an overarching role in the buildings. With modern ideas and glass shutters changing the design profession, jaalis were forced to the back seat.
Researchers have already proved that the indoor air movement can be scientifically controlled by careful positioning of openings in opposite directions following the principles of Venturi effect. The inlet and outlet sides are provided with varying sizes of voids to ensure air in the windward direction moves across the room out into the leeward direction.
Jaalis create climatic comfort also by reducing the solar glare inside. A typically large window gets so bright in our tropical sun that the rest of the room looks dark. The group of small openings in a jaali soften the light.
Though perforated, jaalis could be either load bearing walls or partitions. Few manufacturers have been producing the inclined jaali blocks that provide complete privacy to the interiors, while many architects have also experimented building the wall block itself in an angle, such that no rain penetrates and direct view is avoided. The mason may have to take extra care not to unnecessarily spill mortar or pack the joints beyond the need. Alternately, it is possible to buy the jaali block made with clay or cement. Subsequently, the task of jaali building is like any other wall construction — only the regular brick is replaced by the jaali block.
Jaali walls are still found in all village settlements, for all core and ancillary facilities like house, school or the production shed. The city contexts may limit the use of jaalis due to proximity of houses or apprehension about security when all the residents work, leaving the place locked the whole day. However, jaalis are yet an eminent possibility even in a city, especially in public buildings like schools, institutions or government offices. Also, residential walls enclosing ancillary areas like wash, utility, taller wall tops, family spaces, and such others can have jaalis, beautifully contrasting with the rest of solid walls.
The modest jaali wall can bring in so many amazing features
Old is gold: These walls let in light and air but provide privacy
Where do we find a sunlight breaker, natural air conditioner, money saver, privacy provider and pattern-based wall decorator all rolled into one? In all probability, the search may end up in a jaali wall, as the only answer to the above query. If so, is it a wonder solution? Have we all seen it? Of course yes, yet most of us have forgotten about this amazingly versatile method of construction.
Jaali walls are built with the normal bricks or any other masonry material by placing them with gaps in between either horizontally or vertically. Often these bricks can be placed at an angle also to avoid the direct view into the space inside. Remember the old films where a film heroine would peep through the ornate wall with small holes within, socially not allowed to come into public. Gone are the days of depicting heroines in such manner, but the wall with holes still continues to be around. Wood-carved screens, wooden windows assembled with small timber sections, stone jharokhas, pre-molded clay or cement block with voids, open brick wall and all such others are like first cousins, related to each other, in the jaali options.
The way jaali wall lets in soft light in subdued rays, the way a gentle stream of air flows through the room, and the way outside is visible without letting any inside view are unparalleled in construction options. Accordingly, in the traditional architecture, perforated walls as room enclosures are found all over the Indian sub-continent in diverse places such as Kerala in south or Nepal amidst the northern Himalayas. Incidentally, both the quoted places are legendary for their timber architecture. Padmanabhapuram Palace, with its innumerable wooden jaali windows, appears more porous than solid. Nepalese Mewar architecture style, located in a totally contrasting context, has intricately carved windows set within thick mud walls.
Why has the use of perforated walls declined? There was a time during the last century when civil engineering dominated building design in India, specially modelled after the British systems, which ignored numerous traditional construction practices. Being a predominantly architectural element, jaali appears to be one among the victims; giving way for the PWD-approved normal solid walls punctured only with formal windows. Also, the compact residential neighbourhoods demanded greater privacy and security when the house needed to be locked up during the day time.
The credit for popularising jaali walls generally as an integral part of modern architecture, specifically in Kerala, goes to architect Laurie Baker. Of course, these semi-open walls perfectly fitted the context, besides being cost-effective just as Baker desired. His buildings exhibit different jaali patterns evolved for the specific function, thereby creating a new aesthetics in the design of the structure. Inter alia, he proved how jaali walls are appropriate even in the architecture for today.