Windows are more than mere openings in a facade; they are the dynamic interface between a building and its environment. Like the eyes of a human face, they frame views, dictate perception and influence interaction. Beyond aesthetics, windows serve a deeper, almost respiratory function – facilitating airflow, regulating daylight and ensuring a balanced indoor climate. In an era where sustainable architecture is paramount, the design and treatment of fenestrations must be approached with precision and intent.
The building sector accounts for 40% of global carbon emissions, underscoring the urgency for architects to move beyond carbon-neutral to carbon-negative designs. Fenestrations, often overlooked, play a pivotal role in this transition. By integrating high-performance glazing, optimal window-to-wall ratios (WWR) and parametric shading systems, architects can craft energy-efficient spaces that breathe naturally while reducing reliance on artificial climate control. Additionally, façades must incorporate biogenic materials such as Cross-Laminated Timber (CLT), hempcrete and mycelium panels, which not only enhance sustainability but also actively sequester carbon.
Facades: More Than An Aesthetic Envelope
Modern facades are no longer passive enclosures but active, climate-responsive systems. High-performance windows can significantly cut energy loads by minimising heat gain and maximising daylighting. Triple-glazed, low-E and electrochromic glass technologies offer superior thermal insulation, while kinetic façades adapt dynamically to external conditions. Double-skin façades and phase change materials (PCM) further enhance thermal regulation, reducing energy consumption. High thermal mass materials such as rammed earth, compressed stabilised earth blocks (CSEB) and aerated concrete contribute to passive cooling.
Fenestrations: Energy Optimisations Through Smart Openings
When fenestrations are designed with a holistic approach – factoring in orientation, materiality and airflow patterns – they become powerful tools in achieving sustainable, high-performance buildings. To achieve carbon negativity, fenestrations should be designed with these key considerations:
- Material Selection and Glazing Efficiency: The choice of glass determines thermal insulation and energy efficiency. Low-E coatings, triple glazing, and dynamic electrochromic glass help regulate heat gain while optimising daylight penetration. The U-value (thermal transmittance) should be maintained below 1.1 W/m2K for superior insulation in colder climates, while Solar Heat Gain Coefficient (SHGC) values below 0.25 in warm regions limit heat ingress. Visible Light Transmittance (VLT) between 40–60% ensures optimal daylighting, whereas Overall Thermal Transfer Value (OTTV) must be controlled under 35 W/m2 for commercial buildings.
- Optimal Window-To-Wall Ratios (WWR) And Placement: A strategic WWR enhances daylighting while maintaining energy efficiency. Studies show that optimised fenestrations can reduce artificial lighting dependency by up to 60%. North-facing windows should maintain a VLT of 50–70% for balanced daylight intake, while west-facing glazing should integrate shading coefficients below 0.35 to minimise heat gain. External Effective Thermal Value (EETV) metrics help guide façade optimisation, ensuring energy-efficient placement.
- Natural Ventilation and Airflow Design: Windows act as passive ventilation channels, reducing the need for mechanical cooling. Cross-ventilation strategies, stack effect principles and operable openings enhance indoor air quality while mitigating heat build-up. Mosquito mesh integration and insect screens with an optimal 40–50% porosity ensure airflow without obstruction. Louvered vents with an air exchange rate of at least 5 ACH (Air Changes per Hour) further improve passive cooling performance.
- Responsive And Adaptive Shading: Static shading often falls short in optimising thermal comfort. Parametric shading devices and kinetic façades adjust dynamically to solar angles, ensuring optimal heat and glare control throughout the day. Shading coefficients below 0.4 are essential for high-latitude zones, while adaptive response metrics dictate shading efficiency based on real-time solar conditions.
- Privacy Versus Views: A Technical Perspective: Balancing privacy and transparency requires strategic material choices and positioning. Laminated glass (with a 35–45 STC rating) enhances sound insulation, while toughened glass ensures impact resistance. Annealed glass, though cost-effective, has limited thermal performance. Optical Outward Transmission Value (OOTV) should be below 0.5 for controlled transparency in private spaces, ensuring both privacy and daylight optimisation.
- Fenestrations As Energy Optimisation Systems: Smart window solutions go beyond traditional design. Building-integrated photovoltaics (BIPV) allow windows to generate clean energy. High-performance glazing coupled with optimal shading reduces heat gain, while parametric shading and kinetic façades dynamically adapt to external conditions, optimising solar gain, glare control, and ventilation. Additionally, integrating phase change materials within glazing systems further reduces cooling loads. By absorbing heat during the day and releasing it at night, PCMs minimise the need for air conditioning and heating, reducing energy use.
Bhawar Residence – A Carbon-Negative Prototype
Bhawar Residence is a smart, energy-efficient home, designed to achieve a positive carbon footprint through climate-responsive strategies, renewable energy & green infrastructure. Rooted in sustainability, the following key design interventions harmoniously work in creating a cosy, low-carbon living environment:
Applied Passive Design Strategies:
- Rotation of the floor plates by 12° facilitates the Venturi effect and maximises airflow & passive cooling.
- The atrium serves as a natural ventilation core, unifying spatial volumes, engaging indoors with abundant fresh air.
- Self-shading floor plates create an umbrella effect for the façade, assisting in minimising harsh solar radiation and improving thermal comfort.
- Perforated metal screens clad with vegetation cool interiors by limiting harsh solar radiation by 6.85% on the NW and 4.9% on the SE façades.
- A building envelope using AAC blocks and double-glazed windows offers insulating heat gain control.
Renewable Energy For Offsetting Carbon Emissions:
- A 38.9 MW photovoltaic system with 85 solar panels achieves an Annual Energy Performance Index of 6.7 kWh/m2.
- An energy-efficient VRF HVAC system ensures minimal energy consumption and optimised climate control.
Water Conservation And Green Infrastructure:
- An 8.2 cu. L smart rainwater harvesting and greywater recycling unit reduces reliance on the municipal water supply.
- Vertical and horizontal landscaping optimises air quality and carbon sequestration, achieving a green ratio of 30.4%/m2.
Optimised Daylight And Natural Cooling:
- 91% of regularly occupied spaces receive daylight levels over 210 lux, reducing artificial lighting needs.
- The atrium and cascading greenery emphasise the biophilic design concept to enhance cross-ventilation and naturally cool interiors.
Every design element of this stylish, carbon-negative home is aimed at reducing operational and embodied carbon. Designed to inspire a new era of futuristic residential design, this self-sustaining home merges luxury, technology and environmental responsibility in creating a net-positive impact, paving the way for a greener, low-carbon future.
The Future Of Carbon-Negative Buildings
As the industry shifts towards regenerative design, upcoming trends in carbon-negative architecture include:
- AI-powered adaptive façades that respond to climate conditions in real time, optimising heat gain, ventilation and daylight levels.
- Algae-integrated curtain walls that absorb CO2 while generating biofuel, transforming building envelopes into active environmental contributors.
- Self-healing bio-concrete that enhances durability, reduces material waste and extends building envelope lifespan.
The built environment must evolve beyond sustainability to regeneration. Architects hold the power to create climate-resilient, carbon-negative buildings by rethinking facades and fenestrations as active contributors to a greener future. Windows, traditionally perceived as passive elements, now play a fundamental role in this paradigm shift.
As India steps into a future of carbon-negative architecture, how quickly can we embrace these innovations? Are we ready to transform the way we design and build for a truly sustainable tomorrow?
Quick Facts:
- Architects/Designers: Suraksha Acharya
- Firm: Midori Architects
- Project Title: Bhawar Zero Energy Home (BZEH)
- Location: Anna Nagar, Chennai
- Client: Mr. Sanjay Lunked Bhawar
- Architectural Firm: Midori Architects
- Design Team: Ar. Suraksha Acharya
- Project Management Consultancy: Midori Green LLP
- Project Type: Residential
- Plot Area: 3,579 sq ft. (332.5 sq m)
- Built-up Area: 7,810 sq ft. (725.63 sq m)
- Floors: G+3
- Skills: Architecture, Interior, Green Building Certification, Project Management
- Status: Completed, 2025
- Certification Level: IGBC Platinum
- Glazing Type: Double-Glazed Unit (DGU)
- Fenestration Assembly: 6 mm KS II 146 Clear Glass + 12 mm Air Cavity + 6 mm KS II 146 Clear Glass
- Fenestration Manufacturers: LINGEL, SAINT-GOBAIN
- Fenestration U-Value: 1.634 W/m2 K
- Fenestration SHGC: 0.29
- Fenestration VLT: 42.1%
