Effective – Exterior Wall Cladding

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Cladding is an exterior finishing system a skin to a skin or an additional non-load-bearing layer that serves a dual purpose. It not only helps protect the interiors of the building from harsh weather elements but also makes the outside decorative and attractive. The right cladding helps to maintain the buildings weather-tight and cost-effective, at the same time providing thermal insulation, reducing the temperature variation inside the building. It also helps to improve interior acoustics and daylighting.

The cladding can influence the value, sale-ability and safety of the building. So cladding your property effectively is a wise investment that pays both short and longer-term dividends. There are now more cladding systems in the market than ever before. Finding the most appropriate choice may take a little time, but cladding – used creatively and intelligently – is a great way to stamp your own personal style on a property. Ready to invest in new cladding, but not sure where to begin? Here’s our round-up of everything you need to know.

Exterior Wall Cladding – What is cladding?

Mundhra Chemicals, Sonipat, Image courtesy – ADCPL

Is it a surface treatment that we are designing for the aesthetics of the building or we are detailing for increase the build volume?

In today’s context buildings are designed in two ways:

1) Building volume of spaces and then surfacing the building;

2) Design a surface and then detail the internal spaces. In both ways, cladding material or surface treatment has become the prime necessity for an architect to design. Surfaces should be designed with a context and a purpose.

If so then these surfaces should be intelligent surfaces, says Krishna Murthy, Principal Architect, Folds Design Studio.

According to B.D. Singla, Head of Technical Services, Arvind SmartSpaces, the skin of a building (i.e. cladding) has witnessed a huge evolution in its variety and popularity in all building typologies.

The introduction of pre-engineered structures, market demands for speedy project execution, the zest for quality and innovative options, foreign investment, and the stress on getting the global outlook for the Indian companies are the drivers for the demand in the cladding industry.

Why do we need Cladding?

The exterior cladding of any building may participate in many ways to support the building to withstand external/ atmospheric impacts, says Singla – For example:

1. 

   To protect against weather – heat (direct sun or indirect), cold, wind, rains, pollution, etc.

2. To provide thermal insulation to the exterior facade and maintain internal heat load condition.
3. To provide an acoustic barrier against busy urban conditions outside the building.

Earlier, wall cladding was considered a part of visual art, but today it has gone beyond the looks to become a necessity, says Jasmine Handa, General Manager Construction, Tattva Mittal. Over the years, choices, as well as the functions of cladding, have enhanced, Now for wall cladding, there are many options like laminate, plastic, metal, vinyl, and wood, and there are cladding manufacturers available across India.

Even the end users are looking for something that has good quality is sustainable over a time period in all weather conditions, and is cost-effective as well as aesthetically pleasing to the eye.

Trends in the Use of Cladding Materials

The building industry is on the major cusp of change, says Anup Naik, Partner and Director, Space Matrix Application of technology has played a big role in this momentum shift.

The most visible change is in the cladding materials. Traditionally, various types of stone were very popular, though today, the range is enormous: ceramics, aluminium composite panels (ACP), terracotta, Corian, zinc, corten steel, copper, concrete fibre boards, glass reinforced concrete panels, fibre-reinforced plastic, wood, wood composites, exterior grade laminates, glass, LED facades to name a few.

Rapid transformation is seen in the fixing technology of these materials moving away from the traditional wet fixing to dry systems, saving tremendous time in the building cycle.

Agreeing with Naik on the availability of diverse cladding materials, Sushant Jai-Amita Verma, Co-founder, rat[LAB] observes that the market has seen changes in terms of functionality and performance too. With the introduction of pre-engineered structures, the market demands speedy project execution and innovative designs. Wall cladding comes with a variety of uses and functionalities. In the past three years, the market has seen double-digit growth in the use of cladding materials, points out Verma.

Modern cladding material scores in a number of ways like increased protection against weather and pollution, less water absorption, increased mechanical strength, more thermal insulation, improved acoustical properties, etc. The Indian facade market is majorly ruled by glass and stone, followed by aluminium composite panels (ACPs), HPL, fibre cement boards and wood, adds Verma.

Ashwani Khanna, Head – Marketing, FunderMax adds that a few new and innovative materials such as exterior grade laminates (as per EN438-6) give a high degree of design freedom for people who create. Glass fibre reinforced concrete and metal claddings (zinc, copper, and steel) are gaining popularity and shaping the market due to their versatile properties. Some of the key advantages of these cladding materials over traditional ones are eco-friendliness, thermal efficiency, energy renewability and sustainability.

Metal cladding with lights, Image courtesy – BES Consultants

According to Ar. Reza Kabul, Principal Architect, Reza Kabul Architects Pvt Ltd, the old trends of stone, marble, terracotta/clay tiles have come back in fashion. The only difference is that artificial material with these finishes is available in the market now, which look like natural materials, but all don’t have the same feel. Ceramic tiles are one of the materials which are widely used in many projects, he adds.

There are a variety of sizes available from small to large slabs, which facilitate in creating unique patterns in the facade without wastage of material,” says Reza. Also, fibre cement boards are one of the new trends in the market, which come in a variety of finishes, mostly printed replicas of natural marbles/stones/wood. These boards can be used by laser cutting desired patterns or intricate designs to create the required aesthetical look.

With the evolution of organic forms in architecture, cladding materials have also evolved to complement this design style. Apart from aluminium, which is bendable to a certain extent, glass fibre reinforced (GFRP) is used as it can be moulded into various organic shapes, says Rajan Goregaoker, Principal Architect and Director (Partner), GA design.

According to Rajan Govind, Director, BES Consultants, the use of textured materials, metallic finishes and natural materials like terracotta, and stones are some latest trends.

Shabbir Kanchwala, Senior Vice President, K Raheja Corp lists some of the popular cladding materials and their advantages:

1.  Terracotta: This material has an earthy look and is 100% natural. It is fire-resistant and is often seen in heritage buildings.
2. High-Pressure Laminates (HPL): This material is mass-produced, easy to install and is available in a wooden look with a lot of varieties.
3. Stone and ceramic tiles: This material is easily available, is eco-friendly and gives an earthy look.
4.  Facade cladding systems: Aluminium Composite Panels (ACP), glass, metal cladding panels, GRC (Glass Reinforced Concrete), FRP (Fibre-reinforced Plastic), GRG (Glass Reinforced Gypsum), UHPC (Ultra High-Performance Concrete), Stone CNC (Computerised Numerical Control) are some of the latest cladding technologies that are emerging India.

According to Tavishi Rana, Façade designer, HBG Corp, the most common trends are ventilated facade cladding, parametric facades, energy-generating solar panels, GFRC, perforated aluminium panels and kinetic facade cladding. The material for wall cladding can be selected on the basis of application, construction type, material type and end-use.

The selection is done very smartly depending on the location, weather, surrounding area and type of property – residential, commercial, industrial, etc., which can help to plan for the material accordingly. Nowadays, there are materials that are sustainable yet easy to maintain, buildings that are using such materials have a low maintenance cost, points out Handa.

Intelligent & Responsive Cladding

An intelligent and responsive surface is a necessity in today’s context for any building to sustain. Cladding materials can never be earthquake resistant, can be fire resistant, but structurally designed surface materials with a purpose could be. Intelligent façades can be responsive and aesthetical. If the commonly available cladding materials are used intelligently, then they can be responsive and interactive with the environment as they have their inbuilt properties. Their properties can be defined and detailed for sustainable living. Today’s needs are to build spaces with time management, cost, availability and maintenance, and to design with various responsibilities and liabilities. Therefore, a lot of details are scrutinized before execution.

Multipurpose Hall at Satara by Folds Design Studio

Intelligent facade detailing with interactive and responsive surfaces gives the opportunity to design and execute various possibilities. Mechanically/electronically designed Kinetics surfaces are the new trends to build sustainable buildings.

Surfaces designed with calculative analysis on digital software give opportunities to mould many materials with respect to the local climatic conditions. Hence cladding and surface textures can be executed easily. They may not be cost-effective. The purpose of designing and executing such surfaces is to create interactive and intelligent surfaces with various possibilities. Such materials are executed to respond to the environment in precise formats.

These surfaces have more flexibility to control the environment as they can be calibrated. Such surface claddings can also be designed to form structural members for seismic calculations. Landscapes can also be integrated. Such surfaces or textures give the opportunity to design futuristic buildings. Biomimicing nature and reinventing new materials with scientific calculations opens up diverse possibilities to achieve different forms and textures with various energies. These complex structures can be built along with surface texturing with the aid of 3D printing technologies.

Organic forms in façade architecture – Bungalow, Vengurla, Folds Design Studio

The built forms can carry energies, information and technical data of different subjects within reduce lots of service activities and amalgamate with the context. In such buildings, the surface can also become the structural members and carry different loads, which can be seismically calculated and approved along with fire-resistant applications. These print forms can also be designed to conserve and reuse energy. They can also change their forms as per the environmental conditions. With such advanced technologies, the built forms can be controlled by artificial intelligence. (Krishna Murthy, Principal Architect, Folds Design Studio)

Smart Cladding Technologies & Sustainable Buildings

Perforated liner cladding – Tattva Mittal. For many years, architects have been using precast concrete panels, metal screens and timber panels as the main cladding materials, but the focus has shifted more towards sustainability, so those materials that provide cost savings to the client and help reduce the carbon footprint of a building are one of the primary considerations for designers.

Ar. Reza Kabul looks forward to smart solutions for the facade with analysis and reports that can be extracted from modelling the project in the environmental conditions of that location. Maybe in future, there might be cladding solutions with inbuilt sensors that could monitor the health of the building.

“Recently, architects in this domain have been experimenting with different materials and we have seen a few new types of cladding materials such as perforated screens, WPC panels and timber panels being used in low-rise built forms and we are also starting to see an increase in the use of mineral fibre panels replacing the old traditional metal panels. Fritted glass double glazing is also seeing a resurgence, thanks to its versatility and the fact that not only does it provide transparency to the building, it also helps reduce the solar gain of the built form thus reducing operational costs,” says Verma of Rat [LAB].

Vimhans Hospital, Nehru Nagar, Image courtesy – ADCPL

Facade design alternatives have shifted to utilizing dynamic fenestration and shading systems for optimal control of daylight and solar gains, observes LA Murthy, Founder Partner, ADCPL. Integration of dynamic facades with other building systems is one of the many choices that could potentially save energy in buildings.

A dynamic facade or responsive facade is a building exterior that can change in response to its surrounding environment to maximize its performance. In this way, the ‘skin’ of the building is not static, but dynamic and can transform according to requirements. The dynamic facades act as filters between the indoors and the outdoors, facilitating the users providing appropriate shade, sunlight, ventilation and a visual union with the world in motion outside. With the help of new techniques (sensors & motors), facades calculate the elevation angle of the sun and respond accordingly by constantly changing the orientation of shading elements throughout the day.

 

The facade also has a layered design which includes opaque and transparent elements, which can be moved around on top of each other according to the time of day and weather conditions. Overall, the system is made up of a thermoactive wall and three sheets, which can be coated with a maximum of three different functional layers: insulation, thin film, photo-voltaic and sun protection.

 

“Since technology has moved rapidly into the design fold, we are able to simulate various conditions in the buildings and its users may encounter in their life cycle. This knowledge has forced the facade technology, to make itself agile and climate responsive”, says Naik.

With the advancement in technology, we can see dynamic facades that are connected to sun trackers, which respond to the sun’s movement – movable louvres open and close automatically to control light and heat ingress into the built environment, shading devices expand and contract to reduce the glare and heat gain, ventilated facades control the air draft inside the double layer, based on the heat gain to reduce the surface temperature. Building an integrated photo-voltaic facade, generates electric energy, which could work as a sizable offset on the power demand, observes Naik. These aspects have definitely ushered in a new era of the passive right approach in the sustainable design domain of buildings.

Khanna too agrees that smart cladding systems are used for optimizing temperature levels inside a building nowadays. The materials used in the cladding system are with low U values. To make a project sustainable, energy conservation is of primary importance. Glass facades incorporate Lo-E technology in colder climates where the glass allows heat transmission but does not let the heat escape; in warmer climates, performance glass is used which reduces the solar factor improving on air conditioning cost, observes Goregaoker. Sun breakers on the facade are aesthetical elements that, at the same time reduce the heat gain in buildings.

The Zen Ladakh Resort, Leh, Image courtesy – ADCPL

The implementation of smart cladding technologies not only curbs the building’s energy consumption but also helps improve safety, comfort and security for the residents, adds Kanchwala. Intelligent facades have the ability to adapt to the local weather. These allow users to take control of its performance as per their needs such as shielding during extreme heat and opening up during cool weather.

Furthermore, the use of louvers in cladding provides diffused light into certain public areas which allows air movement, thereby reducing the need for air conditioning in certain areas of the building. Cladding with insulation cavities can also help reduce energy consumption and heat ingress into the building. Kanchwala adds that locally available cladding materials are beneficial as they do not require long-distance transportation and help save the cost of fuel. The colour of these materials also affects the total heat gain. Furthermore, the sun path plays an important role in deciding the glazed and the non-glazed component of the facades.

Ventilated Energy Conserving Facades

According to Rana, recent smart technologies for cladding, including solar energy generating panels and dynamic wind facades, can reduce the carbon footprint and energy loads of the building. These cladding technologies in the future will have a huge role to play in making buildings “zero energy”. A more “frugal approach” would be, the use of waste plastics, recycled steel, and broken tiles as cladding materials for new buildings, she adds.

Ventilated Energy Conserving Facades 

Sunset Streaks – A project by FunderMaxAccording to Ar. Goregaoker, ventilated facades incorporate a technology where the cladding system is installed at a certain gap from the building face and the system itself has vertical gaps between the cladding materials so as to let the natural airflow in the space between. Ventilated facades are a complex, multi-layer structural solution that enables the “dry” installation of ventilated walls. This reduces the amount of heat that buildings absorb in hot weather conditions due to partial reflection of solar radiation, says Amit Murao, Partner, ADCPL. The heat is absorbed by the covering, the ventilated air gap and the application of insulating material.

This, in turn, helps in achieving a considerable reduction in the costs of air conditioning. Vice versa, in winter, ventilated walls manage to retain heat, resulting in savings in terms of heating. Handa too agrees that the process achieves a well-ventilated facade cladding that involves combining a substructure and an insulation layer to the support wall that covers the building by means of a port structure (mainly made of aluminium).

Optical and mesmerising – A project by FunderMax

By employing a ventilated energy-conserving facade, an energy concept can be developed for each building that ideally combines heating requirements for winters, cooling requirements for summers and the perfect daylight quality, note Murao and Rana. Ar. Reza Kabul adds that ventilated cladding is easier to maintain in which the panels can be replaced without effort as they are generally fixed on the aluminium framework with clips.

Due to the partial reflection of the sunlight and air movement behind the panels, the amount of heat that the building absorbs is reduced, thus reducing the consumption of air conditioners, which is a step towards sustainable development. Kanchwala agrees with this, adding that ventilated cladding has relatively low maintenance, and the ability to reduce water absorption into the building, resist pollution and increase the mechanical strength of the building. Energy generation through the seamless integration of photo voltaic and fire resistance are plus point.

Rear Ventilated Facade Systems are installed on substructures that leave ample space between the wall and the panel. During monsoons, this facade system drains the rainwater away from the walls. It is a sustainable system and can help reduce the power consumption of AC in buildings. It creates a gap between the building wall and facade, which reduces the overall U factor of the system by allowing active air movement, explains Khanna. This improves heat and noise reduction while also imparting better weather protection.

Ventilated cladding allows for taking in diffused light, and reduces glare and exposure to dust in the window system behind it. Good thermal and vapour barrier performance increases the building’s life and in some cases increases the quality of the air surrounding the facade. The main purpose of a ventilated facade is to create an interface between the interior and the exterior environments.

Rain-Screen Cladding – Details & Advantages

According to Murthy and Khanna, a rain-screen cladding system is a form of double-wall construction that uses an outer layer to keep out the rain and an inner layer to provide thermal insulation. It prevents excessive air leakage and carries a wind load. The outer layer breathes like skin while the inner layer reduces energy losses. The main benefit of rain-screen cladding systems is that it protects the structure of the building, whether it’s a steel frame or masonry-based system, from the weather elements, especially rainwater. It does this because the cladding panels form a barrier to rainwater, preventing it from penetrating across the rear ventilated cavity and reaching the exterior wall of the building. This process is helped by air continually circulating up through the ventilated cavity, driving away any moisture that penetrates between the panels, upwards and out at the soffit level before it reaches the building structure.

The rain screen assembly allows for water to get past the outer (face) barrier to weep down and outward (gravity assisted and pressure equalised) once the wind abates through a series of engineered flashing and weep assemblies, explains Sushant Verma. The key to this system is to allow for pressure equalization behind the face materials which will allow the water to drain away instead of continuing its way through the wall assembly.

According to Ashok Kumar Bhaiya, CMD, Aludecor, with rain screen cladding, which acts as a ventilated facade as well, there is no need for any weather sealant to be used. The air gap between the building and the rain screen creates pressure equalization which will not allow any air or water infiltration. Appropriate pressure equalization also helps in minimum undulation in metal composite panels.

According to Govind, rain screen is a terminology used to refer to a building envelope, not necessarily a watertight system, The main function is to protect direct rain and is used for common or service areas of the building. Otherwise used for architectural or choice of external finishes.

Reza Kabul notes that its advantages are similar to ventilated surfaces and also their design parameters, only the terminology defers as per climatic conditions. Care has to be taken such that the system is designed to provide proper drainage for water that can get collected in the cavity of the structural support system for the cladding.

Rana says that there are two basic types of rain-screen cladding – drained and ventilated rain-screen and pressure equalized rain screens. The drained and ventilated rain screens require a sufficient level of detailing so that the water in between the cavity can vent outside, whereas the pressure-equalised equalized rainscreen allows movement of air inside the cavity so that water evaporates itself.

Shreepati Arcade at Mumbai – A project by Reza Kabul Architects 66 WFM

A rain-screen facade consists of a ventilation cavity of around 25mm right behind the cladding panel, explains Kanchwala, preventing energy loss and structural decay. The insulation can be positioned within the cavity and the openings at the top and bottom of the clad, which can allow the evaporation of moisture vapour and drainage.

External wall insulation is superior in performance as it eliminates the condensation risks associated with internal or cavity wall insulation. This is important for renovation schemes and in new construction, the use of back ventilated rain-screen cladding provides the designer with the opportunity to use economical single skin load-bearing block work for infill walls.

Most wall systems (brick and stone veneer, siding, EIFS, cement board, etc.), says Verma, are designed to work as part of a rain screen wall system – there are few barrier walls left, other than precast concrete panels, which have a rain screen caulking system that helps drain these assemblies.

Le Meridien – Exterior Cladding Design

According to Goregaoker, a wide range of metal and metal composite materials (MCM) can be used to manufacture rainscreen cladding systems. They can be of aluminium or other metals such as copper, zinc and stainless steel continuously bonded under tension to either side of a thermoplastic or mineral core. Adding to this, Handa says that rain-screen cladding keeps the underlying structure dry, which means less maintenance as there are fewer incidents of rust or corrosion on metalwork.

Advantages of Rain Screen Cladding:

1. Accounts for improved thermal performance of the building
2. Enhances water management
3. The use of lightweight facade materials like aluminium panels means that the loading on the underlying building structure is much less than masonry-based materials
4. Modern rain-screen cladding systems are lightweight and strong, making it relatively easy to create engaging, striking designs that appear to defy gravity
5. All rain-screen cladding material is lightweight in nature and also accounts for easy installation.
6. Modern rain-screen cladding systems allow individual panels to be removed, giving your maintenance team easy access to services

Disadvantages of Rain Screen Cladding:

1.  An additional load is being applied to the existing structure
2. The internal structural elements have to be designed and executed, ensuring the provisions for external facade or screen element fixing requirements
3. Additional cost part
4. Improper joinery and fixing may cause water seepage and corrosion of metal elements
5. Should be used for vertical surfaces only rather than for horizontal or skyward-sloping surfaces
6. Specifications and contracting methods need to be closely coordinated and controlled to ensure satisfactory performance of the entire system

Materials & Methodologies for Fire Safe & Earthquake-Resistant Cladding:

Fire Resistant Cladding

Facade materials play a key role in fire safety, as it would be extremely difficult to control the building fire on the exterior. Hence, more focus is needed in selecting appropriate materials, and this requires designer knowledge of material behaviour and performance points out Murao. Such materials used for external cladding should have been tested for their combustibility, ignitability, flame spread and burning droplets.

Before making buildings more earthquake-resistant, we also need to consider earthquake-resistant cladding as it is the future of construction design. Lightweight wall cladding reduces the forces exerted on the structure and foundations when the building is subjected to lateral seismic loads. Lightweight sheet cladding on buildings tends to rely on the flexibility of the fixings to the frame to accommodate lateral distortions of the structure, says Murao.

Rana observes that the most common way of the spread of fire is – spreading by the material of the cladding and via the air gap. The easiest way to ensure fire safety in buildings is by using fire-tested and rated materials for cladding, compartmentation of cladding areas so that the fire does not spread, cavity barriers, and use of high fire-rated insulation for cladding.

As NBC stipulated the flame spread index (FSI) on the surface of the cladding material has to be considered, notes Ashwani Khanna. Windows and glazing junction areas are vulnerable areas from which fire can spread into the building. Exterior grade laminates are flame-retardant material that doesn’t propagate fire. Further, covering the windows and cladding junction with a fire seal reduces the scope of fire spread on the façade or into the building.

In case of a fire, the exterior walls get susceptible to radiant and convective heat which quickly transfers a ground fire to the structure’s roof, elucidates Kanchwala. To combat this, the exterior walls can be protected by fire-resistant materials such as stucco, plaster, cement, and concrete masonries like brick, stone or blocks. The key points regarding fire safety are to prevent the spreading of smoke and fire in the building. Suitable fire stops and smoke seals play a crucial role in preventing the spreading of fire. Provision should be made for required openings for safe evacuation and passage of smoke. The framing which grasps the cladding makes it strong and prevents the structure from collapsing during a fire spread.

 

According to Handa, well-constructed buildings can help prevent tragedies due to fire by using materials that are relatively fire-resistant. Materials nowadays are rated in the order of their ability to restrict fire from affecting the structures. Hence the smart way is to construct a building in which a fire would take effect slowly, allowing the occupants plenty of time to escape in emergency situations.

Govind says that cladding material shall not use combustible or character of fire propagations. For these risks materials such as timber-based are not recommended for cladding. Commonly used ACP must be selected carefully such that the material is free from combustible polyethene (PE) core. Due to recent fire instances in a few international buildings, there is greater awareness of Fire Retardant ACP (FR) panels, which are recommended instead of PE core ACP materials.

With regards to fire-safe cladding material, a minimum of two-hour fire rating on materials is required, points out Reza Kabul. Since the fire in the Address Hotel in Dubai the industry is moving away from ACP as a cladding material and heading towards tiles and high-pressure laminates, he adds. For earthquake-resistant cladding, notes Kanchwala, the material selected needs to have movement and should resist lateral forces. It is mandatory to select the appropriate façades during the stage, with the use of a unitised glazing façade that is often used in tall towers to resist movement.

 

Earthquakes generally have no direct impact on cladding materials and their choices, however brittle or stiffer materials are not advised for high-risk seismic zones, says Govind. Furthermore, the seismic-resistant design of cladding systems will have to take care of supporting systems and fixings to the building. For earthquake resistance, explains Reza, the cladding needs to be dry cladded onto the building and the joint should not be rigid but account for movement due to earthquakes. The material should not crack and fall during an earthquake. The thickness of the material plays an important part. For tiles, they should be 10mm plus. High-pressure laminates, even though they are thin,they are very flexible and do not break easily.

Fire testing of cladding materials 

Sushant Verma stresses the need for testing the materials for extreme conditions and making the necessary corrections before installation. The role of independent performance and fire testing labs has gained importance in the last few years. These testing labs are for simulating weather conditions as per the design criteria and putting up a mock-up sample through a series of tried and tested procedures to validate the theoretical assumptions used during design. After the testing in the laboratory, the facade approval is given to the façade contractor to begin the installation of the facade at the site. Many testing specifications have been designed to test the facades over the last few decades, a few of them are ASTM, AAMA and ASNZ.

The cladding design intent should be to prevent the fire from spreading in the building, notes Khanna. The aspect in fire propagation is as per NBC, BS 476 part 7 for cladding material and preventing fire ingress through an opening in the cladding structure, e.g. windows, glazing junctions etc. The ingression through the opening in the cladding structure can be addressed by providing a fire seal, preventing the fire/flame from entering inside the cladding cavity. The material property prevents the surface fire from spreading.

 

Exterior compact laminates are manufactured in accordance with EN438-6 a flame retardant material and the flame spread Index (FSI) is less than 25 as per ASTM E 84 ensuring that the norms of surface flame spread adhere. The cladding material should not release any toxic fumes, should not be dripping and should follow all standards as per NBC.

The curtain wall structure is a multi-storey structure where exterior walls are not a part of the load-bearing structure. As the common construction methodology, the floor slab is supported by interior beams and columns. We mostly encounter a perimeter void typically in the range from two to eight inches between each floor slab and exterior curtain wall, observes Verma. Perimeter voids are hidden from view after construction, but when such openings are left unprotected they provide the perfect space for fire and smoke to spread upwards.

Fire norms provide guidance on the different fire rating classes and testing of cladding materials, says Rana. These norms are specific to different types of buildings and the number of floors a building has. In ordinance with the European standard EN-13501-1, the cladding panels can achieve a classification from A1 to D, A1 being the most resistant to fire.

Most of the challenges are faced in the selection of materials that fit the fire safety norms, says Reza Kabul. As a standard, most of the vendors provide 2-4 hours of fire resistance for the cladding materials. Care has to be taken during the installation process with proper fire stops, which need to be designed on every floor. Advancements in the software help us to design critical junctions, complex designs and parametric facades with better efficiency & safety.

According to Ar. Goregaoker, concrete is an excellent fire-resistant material. It is non-combustible and has a low thermal conductivity which means a fire will take a long time to affect the structure, giving time for evacuation and protection from the spreading of fire. Concrete is not a very stable material to be used in earthquake-prone areas. So, steel-reinforced concrete is used as an earthquake-resistant cladding material. Aluminium itself is a bad conductor of fire, but the core within the panels is susceptible to catching fire and therefore the new technology of using fire retardant core and making the ACP panels fire retardant is now a common requirement. Also, proper designing of smoke seals and implementation is necessary to prevent smoke from travelling from one area to the other.

Fire Safety – Norms & Standards 

These days, with the rise in high-rise buildings, safety norms and product verification are of utmost importance, says Goregaoker. Fire retardant materials, and checking for combustibility are some standards we need to maintain while choosing our facade material. According to Reza Kabul, the norms & standards to be followed is the one by the Bureau of Indian Standards (BIS). Generally, the cladding material is selected based on the test and quality certificate provided by the vendors. If further quality control is required, the physical samples are tested by independent labs to confirm the materials.

Fire safety norms are being taken seriously worldwide. In India, the National Building Code 2016 has made lots of changes. Still, a lot of work is required in the case of cladding material as this portion still remains challenging, notes Ashok Kumar Bhaiya, Aludecor. According to NBC, we require 2 hours of fire resistance in cladding for fire separation of less than 3.7m.

In other parts of the globe, where the density of buildings has increased and fire separation is less than 3.7m, the cladding material used is A2 – s1, d0 grade of EN13501- 1. These materials need no testing for 2 hours as they will not catch fire at all and there are no chances of smoke or droplets. In a country like ours, where the cities are old and unplanned having high population concentrations, only Firewall A2 should be used for cladding.

Every country or region follows different fire classifications and certifications like ASTM E 84, BS 476 Part 7, NFPA 285, and BBA. The class of the cladding material under standard fire classification norms must be considered while choosing, says Khanna of FunderMax.

According to the International Fire Stop Council:

1.  A properly designed & tested perimeter fire barrier system not only protects the perimeter joint but critical wall framing and support elements as well
2. All model codes call for the rating of the floor to extend to the exterior wall
3. All model codes require minimum spandrel height
4.  All model codes allow spandrel height exceptions in certain sprinkler conditions
5. Designing the wall to keep the fire stop system in place for the rated period of the floor is an obvious necessity
6. Designing and installing the fire stop correctly is the final step
7. Joints move and may present a weakness in fire containment

BIS Standards & ECBC norms for Cladding Materials

 BIS codes are generally referred to for technical details and submission guidelines, which are required to get necessary approvals for the fire safety of the project. BIS standards for cladding materials follow the British norms of material classification for fire safety, to be rated as Class 1 as per BS 476 part 7, notes Khanna.

ECBC (The Energy Conservation Building Code) has set specific parameters for constructing an energy-efficient exterior facade of a building, points out Handa. The norms specify that a building can be up to 60% covered with glass, in which case a superior quality glass is preferred that is good for thermal performance. ECBC standards are incorporated in the design by making the simulation model in the software which helps the project to make it energy efficient. All parameters of the facade are checked, and solutions are created to check the maximum efficiency.

According to ECBC norms:

• Glazing panels should be provided with tempered glass for venting out fumes and for fracturing the glass into smaller pieces.
•  The space between the slab and facade spandrel is to be provided with fire stops and a fire-rated GI backup panel to stop the fire from travelling from one floor to another.
• Knock-out panels should be installed, which are identified by non-removable reflective dots located on the lower corner of the glass to be visible from the ground to the firefighters.
• In case of falling glass from the affected floor providing tempered/toughened or laminated glass is the best protection.
• The glass proposed to be used for internal fire compartmentation should be either low-radiation or insulated fire-rated glass.

The National Building Code (NBC) specifies that the surface flame spread index of cladding material should be less than 25 as per ASTM E 84, Class I.

There are several international standards, widely referred to for cladding materials are EN 13501, ASTM E84, BS 476 Part 6 & 7 and BS 8414. These standards specify fire and smoke spread characteristics and acceptable norms with testing standards.

Conclusion

Cladding acts as a protective barrier around the outside of a building to help regulate the interior atmosphere, preventing external elements from affecting the main structure while creating a pleasing aesthetic appeal. Designing the facade of a building is a complex task due to the multiple criteria to consider – like the availability of a variety of materials and technologies for cladding, safety and security factors, and the number of stakeholders involved. The most important requirements while choosing cladding materials are performance, appearance and good warranties against fire, wind and seismic activities.

The decision for the cladding material is mainly influenced by building type, client requirement, geographical and climatic aspects of the location (or the project context), product availability and reputation, product cost, client’s budget and project delivery methods. The main issues with cladding are maintenance, the quality of the materials, fire safety, weather tightness, etc. This article highlights the key influences and issues related to the selection of cladding materials for buildings.

New Cladding System to Save Energy

Recently, two researchers have developed a ventilated facade with a double chamber and flow control device that significantly saves energy in buildings. This sustainable, efficient solution can be applied in both renovations and new buildings due to its simplicity. Conventional ventilated facades are composed of an inner sheet, thermal insulation, ventilation chamber and exterior finish. The new facade adds a second air chamber between the existing one and the facade insulation.

Both chambers are interconnected by the bottom of the facade. Another feature is a new element at the top to regulate the airflow in the chambers, depending on the gradient of the existing temperature between the inside and outside of the building. This presents two improvements over conventional systems. Energy gains/ losses are reduced through the facades, consequently, reducing the energy consumption due to airflow. Secondly, the design of the system helps to reduce the vertical temperature gradient along with the envelope, homogenizing the air temperature in the chambers throughout the year.

 Classy sophistication – FunderMax Project

A studied choice of material is made adhering to the following points:

• A tested fire resistance level of the material and the system – Fire resistance levels are calibrated to minutes for structural stability, integrity and insulation • Combustibility parameters and fire hazard properties need to be prescribed as a mandatory checkpoint for cladding materials
• Compliance with the fire laws and the specifications in the national building code should be a prerequisite
• Spandrels, insulation and horizontal fire barriers should be fire-rated to prevent vertical transmission of fire
• Test reports and certificates from a registered testing authority for cladding materials should be made mandatory
• A key aspect that does not get addressed is the maintenance, as the building ages the systems suffer fatigue, and most often fire barriers, joints and insulation give way and lead to fire leaks. A maintenance policy should be a prerequisite for any building sanction
• Guidelines for product properties focusing on hazards, encompassing linings assemblies and materials (Anup Naik, Partner and Director, Space Matrix)

New-Age Cladding Materials are Rapidly Gaining Ground

An interview with Shankho Chowdhury, Executive Business Head, Decoratives, CenturyPly

Please brief on the latest trends in cladding materials

Although the traditional wet facade elements such as bricks, stones and wood are still widely used and have a ready market, new-age elements and composites around ceramic, vinyl, and fibre cement are also rapidly gaining ground. Technological advancements and novelties in the industry are aiding in evolving consumer preferences. Currently, high-pressure laminate cladding and stone veneers are the most popular cladding options in India. Other than this, metal claddings are also in the trend, mostly for commercial buildings and factories. Using fibre cement as a cladding element is still a new concept in India and we believe it has a huge scope and its market is growing rapidly.

Tell us about smart cladding technologies for sustainable buildings

Arena Space by GA Design

New research on nanomaterials, bio-materials and smart composites imitating natural nanostructures and processes is trialled almost every day within the radical technologies. In the architectural field, and especially in the sector of building cladding, only a trivial amount of such advanced technologies has settled. As an alternative to traditional mechanisms and techniques, architects and civil engineers are nowadays using enhanced composite materials to provide crafted and efficient facades.

What are Ventilated Cladding & Energy Conserving Facades?

The building envelope and the building services system are mostly responsible for deciding the building’s energy efficiency. There have been advances in facades, designed for introducing the air crater to improve the facade performance, such as Double Surface Facade (DSF) and Opaque Ventilated Façade (OVF). The DSF consists of manifold glazing layers and the OVF consists of the primary wall and an additional cladding, which can be added both externally or internally.

Artistically utilizing the exhaust air of indoor air conditioning systems to flow through the ventilated facade can further enhance the facade’s thermal performance. Composite materials like artificial stones, solid surfaces, laminates and other less-known elements are usually adopted for ventilated facade solutions and help projects achieve high levels of building sustainability certifications.

Please tell us about materials & methodologies for fire-safe and earthquake-resistant cladding.

Cladding material plays a pivotal role in building a fire and earthquake-resistant structure. It is always advisable to pay attention to the core while selecting cladding materials. For fire-retardant cladding systems, the core should be non-combustible or at least semi-combustible. Planks or weatherboards made from fibre cement or steel, Greenguard-certified HPL panels, aluminium and re-constituted timber products are some of the materials for fire-retardant cladding.

For the earthquake-resistant cladding system, the cladding materials should be lighter to make the structure resistant to sideways loads. Materials such as fibre-cement, PVC or aluminium can be used for this purpose. Sheets and panel materials made from plywood can also make a difference. Alike lightweight roofing, because of their lower mass, lightweight wall cladding lessens the forces exerted on the structure and foundation when the building is subjected to lateral seismic loads.

Tell us about the importance of fire-safe design, materials and technologies

Materials used for cladding affect the vulnerability to fire as otherwise, it would be extremely difficult to control the fire on the exterior. Hence, it is always advisable to select appropriate materials for cladding, considering the industry standards, material behaviour, combustibility and performance. Usually, in India, most of the material procurements in facades are based on budget and not specification-centric, which not only endangers the structures but also the surroundings to high risk.

While choosing materials for fire-retardant cladding one should always focus on the core of the material, which should have combustibility. The specially formulated double-hardened resin, which is used for the impregnation, contributes to the fire-safety property of the product.

Brief on Fire Safety Norms and Standards to Consider

There are different norms and standards considered for different materials used. However, EN 438 – part 6 & ASTM E84 can be mentioned.

Tell us about the Market for Fire Resistant Cladding Material

Consumer awareness for fire-resistant cladding is growing rapidly in India and this is imparting a positive impact in the market. Evolving requirements are influencing the available choices of fire-retardant cladding options. At present, the market has a varied variety of fire retardant HPL panels, which also come with Green-guard certification. This qualifies these products to be used in ‘Green Buildings’ and in other delicate environments such as schools and healthcare institutions.

Fire Rated Cladding Materials

Fire-rated/retardant or resistant materials for cladding are selected on the basis of not only fire resistance, but the aesthetic appeal as per the design intent of a building, the climate of the region where the building is located, the cost and requirements to safeguard from fire for a certain duration, etc. Some of the key materials and their ire resistance basics are stated below:

Fire Retardant Aluminium Composite Panels (ACP)

These ACPs are available in various colour options with thermal and sound insulation layer properties. The fire rating is done as per the European and British standards, i.e. EN13501-1-B1 Grade, BS476 – Part 6 & Part 7. The coating thickness would be approximately 30 to 35 microns. Some of the manufacturers provide ACP sheets that do not release excessive heat onto other adjacent materials which can cause a fire.

It is mainly made of inorganic materials and the density of non-combustible content in the core is to be 70-75%. These external cladding panels will not contribute to the rapid spread of flames towards the upper floors of the building. It can withstand fire for two hours, as exterior cladding of typical Indian construction.

Stone Cladding

Stone is a non-combustive material in terms of catching fire. The fixing base in the wet cladding system would be a cement & sand mixed mortar while in the dry cladding system, a clamp with a fastener is provided onto the base wall and takes a load of stone slabs above 15 to 25 mm thickness. However, there are many drawbacks to stone as a fire-resistant material. Hot stone when subjected to sudden cooling develops cracks and can lead to failure of the structure. For example, granite, when exposed to severe fire, explodes and disintegrates. Limestone is least recommended as it crumbles and gets ruined by ordinary fire. Only compact sandstone having grains may be used as it can stand the exposure to moderate fire without serious cracks.

Brick Cladding

Clay bricks are one of the oldest construction materials used in many ways for external cladding purposes. It is used as a load-bearing element when constructed as a wall with appropriate thickness and also used as an exposed cladding material withstanding against temperature drops, rains and pollution. First-class bricks moulded from good clay can stand exposure to fire for a considerable length of time. The properties of bricks that render them fire resistant are the size of bricks, the method of construction and the component of fire resistive material in bricks i.e., clay. It has been well established that brick masonry construction is most suitable for safeguarding the structure against fire hazards.

Fibre Cement Boards

There are exterior grade fibre cement boards with multiple properties like less water absorption ratio, non-combustible/fire resistance, termite resistance and, up to a certain extent, providing sound insulation as well. Locally, many brands are supplying boards for exterior cladding considering its noncombustible aspect.