Passive design is an integral part of energy-efficient architecture. Sophisticated building systems also contribute to this end. But what role do materials play in enhancing a building’s energy-efficiency?“Material selection is one of the earliest opportunities to influence how a building performs,” says Tejbeer Singh, Principal Architect & Founder, Expressionist by Tejbeer Singh. “The objective is not simply to select materials that look appropriate but to understand how they behave within the climate and construction system.”“A material becomes sustainable not merely because of how it is manufactured but because of the work it performs throughout the life of a building,” explains Dikshu Kukreja, Principal Architect, CP Kukreja Architects. “In India, where climatic conditions vary considerably, the same material can behave very differently depending on its thickness, orientation, exposure and relationship with shade and ventilation.”CW evaluates a few materials for their ability to contribute to building performance.Blending materials to push sustainabilityFor Mastiff Select Mandavya in McLeodganj, Himachal Pradesh, a hospitality project in the hills, Singh brought together glass, concrete foam blocks and reclaimed timber to address different aspects of the building’s performance, from controlling heat transfer and reducing structural dead load to making use of resources already present onsite.Double-insulated toughened glass (₹ 300 to ₹ 450 per sq ft) was used to ensure views and natural light, an important part of the spatial experience; and from the performance perspective, to reduce heat transfer and, consequently, the mechanical conditioning required to maintain comfortable indoor conditions. Lighter weight concrete foam blocks (₹ 40 to ₹ 60 per piece) helped reduce the dead load generated by the walls, contributing to a lighter structural system. Reclaimed wood from trees fallen within the property was used for structural arches, entrance gateways, balcony framing, lift-lobby panelling and elements within the suites. Rather than contributing directly to operational energy savings, the value of reclaimed wood lies in retaining an existing resource and extending its material life, and reducing the need for new timber, says Singh.Together with the wider design strategy, he estimates these material choices to have contributed to approximately 15 per cent overall energy savings, with material-related measures accounting for around 5-7 per cent of the total. “Energy-efficiency is not necessarily about finding one material that solves everything,” says Singh. “It is about understanding how different materials can work together, responding to heat, reducing unnecessary load, and making better use of what is already available.”Brick façades as environmental filtersA wider principle in the CP Kukreja Architects practice is that material efficiency does not come from specification alone. It comes from using material intelligently, in the correct orientation and depth, and as part of a larger response to climate. For instance, at Pathways World School, Gurugram, a CP Kukreja Architects project, and India’s first Platinum-rated institutional development, clay brick (₹ 7 to ₹ 12 per brick), locally available stone and insulated wall and roof assemblies were selected in response to the ecologically sensitive Aravalli setting. “The thermal mass of the masonry moderates fluctuations in indoor temperature while the insulated envelope reduces unwanted heat transfer,” explains Kukreja.At another CP Kukreja Architects project, Harrow International School, Bengaluru, a US Green Building Council (USGBC) Platinum-certified project, locally sourced brick (₹ 20 to ₹ 30 per brick, depending on its dimensions, finish, strength, firing quality and the quantity procured) establishes the architectural identity of the campus while contributing directly to its climatic performance. Brick jaalis, shaded openings and chajjas filter harsh sunlight before it reaches occupied spaces, reducing heat gain while allowing daylight and air to enter. “Brick was not used merely as a decorative surface; its depth, porosity and arrangement allow the façade to operate as an environmental filter,” says Kukreja.Screens to measurably lower indoor temperaturesPixxel Aerospace’s headquarters in Bengaluru spans 50,000 sq ft. The south facade, the building’s hottest exposure through most of the day, carries a custom-designed perforated metal screen, made of 75×40-mm mild steel sections (₹ 500 per sq ft for 6-mm thick, laser cut and both sides painted), spaced 60 mm apart, set forward of the building’s glazed and solid wall surfaces. Rather than treat shading as a decorative gesture, Deepak Gupta, Director, D R Design Consultants, explains it was used as the first line of defence against solar heat gain, intercepting direct sun before it ever reaches the façade, well before any mechanical system has to work to remove that heat. “The screen keeps the building’s most sensitive spaces, including cleanrooms that require tightly controlled temperature and humidity, meaningfully cooler on their exposed side, and measurably lowers the load carried by the HVAC system as a result,” he says. “It also reads as identity rather than infrastructure; a portion of the screen doubles as a canvas for site branding, so the same surface performing thermally is also the building’s public face.” For an aerospace client, where cleanroom stability is a technical requirement rather than a comfort preference, treating shading as engineering rather than ornament was the deciding factor in this specification.AAC blocks for thermal plus structural advantagesFor multistorey residential towers (G+6) for faculty members and students within the 70-acre Indian School of Business (ISB) campus in Mohali, Punjab, Rahul Bahl, Managing Director, Krishna Buildestates, opted for autoclaved aerated concrete (AAC) blocks (₹ 3,400 per cu m) for the masonry and non-glazed infill envelope. “We opted for AAC blocks over conventional red clay bricks as they offer a combination of advantages, from thermal performance and structural efficiency to ease of execution,” he says. Further, AAC blocks are significantly lightweight, faster to lay, require less mortar, and provide far better thermal insulation than traditional alternatives. As they weigh roughly a third of standard masonry, using them as infill walls across the multistorey towers substantially reduces the structural dead load, which, in turn, helps optimise the consumption of steel and concrete.According to Bahl, the primary thermal advantage of AAC blocks lies in their porous, cellular composition, which provides superior insulation properties. “Our use of AAC blocks drastically slowed external heat absorption during the summer months, while helping to retain indoor heat during winter, thus allowing ambient indoor temperatures to be far better maintained across all non-glazed wall surfaces, directly lowering cooling costs and reducing the baseline HVAC system loads,” he says.Trapped air cavities resist heat transferAt the Ramakrishnan Residence, a 6,000-sq-ft villa in Bengaluru, hollow clay construction on both the walls and the roof, rather than solid brick and conventional RCC, is the primary strategy for keeping the house cool through long, mild but sun-heavy days. For the walls, the construction element was hollow terracotta blocks, 200×200×400 mm (₹ 85 per block). “The trapped air cavity inside the hollow block does the thermal work, breaking the direct conductive path a solid brick wall would otherwise offer,” says Gupta. “The roof carries the same logic through in hollow clay roofing brick, a lighter, more cost-effective slab system than conventional RCC that, by the same principle, resists heat transfer better than a solid concrete roof exposed to direct sun. Treating the wall and the roof as one continuous hollow clay envelope, rather than solving each separately, meant the whole house benefited from the same passive strategy rather than only the parts that happened to get insulated.”Insulation as a protective materialPrihan Plaza, a commercial (retail plus office), four-storey (above basement parking) building in AECS Layout, Electronic City, Bengaluru, spans 15,000 sq ft. The terrace slab, the roof surface most directly exposed to the sun, was insulated rather than left as bare RCC. The build-up runs a 150-mm, 6-inch, RCC slab, 50 mm of rigid XPS insulation (installed at around ₹ 75 per sq ft), a 50-mm, 2-inch, protective concrete screed, and a waterproofing coat over the top, breaking the heat that would otherwise conduct straight down into the top floor office space below. “For a leasable commercial building, where the top floor is exactly the unit a tenant judges on comfort and air-conditioning running cost, an insulated terrace slab was a deliberate, low-visibility way to protect that floor’s value rather than leaving it to carry the building’s full solar exposure alone,” explains Gupta. “The same terrace also carries a partially covered outdoor deck, cantilevered clear of the building’s edge, giving occupants a usable shaded outdoor space rather than an unused hot rooftop.”Clearly, choosing the right materials enhances building performance.