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PRECAST LINTELS

It has been attempted in the past and the recent endeavour by an architect in Mysuru has further improved the earlier ideas.

28bgp-greensens_26_2637392eWe are now living in an age of innovation where the old order is continuously being replaced by the new. Should this sound like a great time, let us remind ourselves the fact that such an age will also be a time of both gains and losses. Large number of time-tested ideas like courtyards and hot air ventilation are rarely found today, despite them being valid even now. However, there is hope in many other items of works, which are still popular, despite being practised in an improvised version.

In many ways, improvisation is also a part of innovation, yet by retaining the original at a conceptual mode, we see our past flowing into the present. The change is more gradual when we effect better finished and more efficiently managed products and services. Many such improvisations happen during construction at site mostly thought out by the project team; as such do not get documented for wider dissemination. Lack of professional efforts to collate the best practices within us compounds this lacuna, hence the potential to upgrade our methods and skill sets gets largely lost.

Lintels can be a good case to illustrate. In the past, the support above any opening like a door, called as lintel, was achieved by stone, wood, door frame itself or totally avoided by having an arch. With RCC lintels being the order of the day even in small villages now, it is time to relook at it.

Options

One option is to revive the past with stone lintels and another could be to avoid them except where needed absolutely, choosing to do cut lintels. In many cases due to site conditions or earthquake considerations, we may need them to run all around the walls at 7 ft. height.

roviding the necessary shuttering, casting, curing and de-shuttering means slowing down the project; letting cement water flow down defacing the wall below and face tricky situations in some cases on the external side of the wall. If the lintel could be precast on ground to be placed on wall top, the task gets much easier.

Each piece has to be cast to the exact wall length needed; junctions between two pieces has be resolved to provide continuity; placement of all the pieces needs to be secure and aligned.

What if we can go one step further in improvising the idea? Let us pre-cast the U-shaped lintel channels on ground, cut them to fit wall lengths, lift and place them on wall tops securely with rich mortar base.

The channel itself acts like the lintel; hence reinforcement rods can be considered only where required. Once the channels are filled with the required mortar mix and cured, further wall work can resume without much delay.

Pre-casting the lintel has been attempted in the past and the recent attempts by architect Rajesh Jain in Mysuru has improved the earlier ideas. There will be further scope too, as long as we wish to better a product.

Lintels and ‘overdesigning’

How to minimise the design to save money and materials?

lintelHow often do we try discussing with the elderly people at home about getting a building done? The general experience is about the difficulties in forging a dialogue, due to differing construction practices from their time to our contexts. We feel there are advances made in these years and many of them feel we are wasting money by ‘over-designing.’

One simple example could be the case of lintels, which are the horizontal monolith members above any opening to support the wall above doors and windows. In the past, these could be with wood or stone, but often we notice there were no members at all – the wall sits directly on the wood frame! The frame takes the load, so why lintels?

Traditionally, carpenters would prepare the door and window frames in advance, before the walls start, such that the requisite seasoning of the wood is complete. As the mason builds the walls, these frames are placed in the centre of wall thickness and the wall continues without any extra lintel member. Even today, we can see such houses standing for centuries. If so, why are we adding the lintel beam, that too in thick and strong concrete?

Horizontal rigidity

Lintels help in tying the building laterally and if continuously placed around all the walls provide a horizontal rigidity to the building, which is a compulsory measure in earthquake-prone zones. However, do we need them all the time in all kinds of buildings, including small houses, in places like Bangalore with least risk of earthquakes? Even expert answers may differ, but reducing the lintels as per context and upon structural engineer’s advice is possible. Every concrete lintels need support by shuttering, time for bar bending and concreting, curing with water and such others, demanding time, money and materials. Can we save on this, even if it’s partly?

Once the walls have reached the lintel level, we can place a wood plank as support, place two M.S. reinforcement rods of required diameter across the opening, pour nominal thin screed concrete, place the bricks vertically with the central three bricks forming a wedge narrowing downwards.

This method uses two concepts – that of reinforced brick beam in terms of steel and principles of flat arch in the brick work. On the top of this flat masonry, two more rods can be placed if heavy loading is expected. For opening up to 5 feet wide, this method can be applied with specifications as advised by engineers. As one sees, there are no concrete beams, delay due to formwork or curing and such others.

Today we design with very high factor of safety, a precautionary approach where nothing may go wrong.  Understandably, this method very often leads to over designing, as the example of lintels may prove. We can think appropriately, minimise the design to save money and materials. To that end, all the three stakeholders, namely the designers, owners and builders, should think alike towards a cost-effective and eco-friendly building.

A rethink on lintels

Over the years, lintels, despite being less talked about, have dictated many aspects of structures and elevation

Minimising material consumption is among the basics of eco-friendly designs. Equally well, it may mean replacing one material by another which could be more effective and less energy consuming. On an overall basis, costs and volumes involved with lintels may not appear very high, hence most builders follow the standard practice. However, the alternative ideas here can not only save time, but create new kind of looks as well.

No plastered bands

Most designers would like to see their stone-walled building not to have RCC plastered bands created by the lintel and RCC slabs. To this end, a thinner version of RCC lintel is cast to be clad by stone on its elevation face, to get an all-stone look.

Where stone slabs are abundantly available, directly placing a stone slab on the opening and then continuing with regular stone masonry is equally popular and most often less costly. In such cases, the stone should be carefully chosen with hopefully no fault line or weak points. Both ideas ensure complete stone looks.

Niche, but not a loft

Creating a wall niche or a shallow shelf within the wall has been around for a long time, offering a practical solution to storage in an attractive way.

Lintel is needed here too, but only for half the internal wall. Often there would be a narrow 2′ wide opening, with very little weight to be borne from above. All such minimal cases can be managed even by two rods kept atop the niche or arched lintels in brick or stone.

The internal loft or storage slab below ceiling level is at the same height as the lintel, hence the two are merged with each other structurally. While casting concrete lofts has been a common practice, we have also realised that they can be dispensed with. When a wardrobe gets fixed to the wall side, the plywood plank at 7′ level, just above the shutter, acts like a loft slab. It may not be able to take all the weights a concrete slab can take, but then none of us can lift such weights even to keep them there! In a household case, most items that go into a loft can be managed by a wooden plank. In case we expect very heavy items, there could be just one concrete loft, or better still, a ground-level storage option.

Key points to note

In kitchens too, with the cooking platform below, lifting heavy items for storage above never happens. With modern options available for kitchen shelf designs, the RCC loft cast at a fixed height can more or less cause trouble fixing other modular units. As such, avoiding concrete lofts saves money and labour.

Over the years, lintels, despite being less talked about, have dictated many aspects of structures and elevation. We realise that the idea of 7′ level, which determines varied issues from human scale to cut-size wood, loft heights to chajja levels and feasibility of arches to air trap zones, is something we just cannot ignore!

The neglected lintels

Continuous RCC lintels have gained popularity, nearly wiping out other solutions

Native wisdom: In a wall with exposed materials, designing the lintel aesthetically is important

Construction practices have been handed over to us from millions of years with millions of methods. This maze offers no help to us in picking the best practices for today. As such, we build today in a bewildering variety and how we build continues the past ideas rather randomly. Imagine a rich kid with thousands of toys, all of which are good for playing. What the child chooses to play with, discard, safeguard or reject is beyond any logic of theory – it is determined only by the child at that moment.

Such a vast constructed precedence enables justifying whatever we do. Lintels are an apt example of this state of confusion, where we blindly follow some past procedure. Most builders give it no thought; hence they are more like a neglected cousin among all wall practices. Only a logical structural engineer and a contextual architect can together question the idea of lintel or design the right kind of lintel beam.

Lintel is a short beam in wood or steel or concrete placed above an opening in the wall, to support the triangular part of wall above it.

It may appear not related to the discourse of green architecture, but it does contribute by being cost effective, following a judicious design. In a wall proposed to be plastered, lintels become invisible after the finishing, but if it is all exposed materials, designing the lintel aesthetically becomes very important.

The recent practice in Bangalore has been to cast the so-called continuous RCC lintel all over the wall at 7′ height, irrespective of the location of openings. In the name of strength, it made beams too frequent; if plinth and roof beams are also around, shooting the construction cost upwards. In the name of tying all the columns, it contributed to frame construction, often unnecessarily. Such intermediate beams also covered up possible weak masonry or low construction quality. To cap it all, it made the life of consultants easy, simply to repeat it in all buildings, without any specific designing and drawing, at the cost of owners. Thus, the continuous RCC lintels gained popularity, nearly wiping out other local and creative solutions.

Option

Can we avoid lintels all together? Yes, if all doors and windows are taken up to roof bottom. We will discuss these tall openings during the forthcoming essays. If the windows are placed first, then casting a formal RCC lintel can be replaced by other on-site solutions.

Can the lintels be discontinuous? Can we conceal them within stone or brick walls? Are there options outside concrete? Let us brood over such queries to get right answers.