Casa Verdante
Project Overview
Casa Verdante holds a unique place in Indian sustainable construction history: it is the first residential project in North India to achieve full Passive House Institute (PHI) certification under the Passive House for Tropical and Hot Climates standard — a rigorous adaptation of the German Passive House standard developed specifically for warm and humid climate zones. That this milestone was achieved in Chandigarh — a city with summer temperatures regularly exceeding 44°C and winters that dip to 2°C — makes it all the more remarkable.
The Malhotra family's brief was deceptively simple and profoundly ambitious: build us a home that does not need air conditioning in summer, does not need central heating in winter, and costs virtually nothing to run. After three years of research — during which Rohit Malhotra, a mechanical engineer, educated himself comprehensively in passive building principles — they found EcoBuild Studio and asked us to make it happen.
The building envelope is the project's defining achievement. External walls consist of a 400mm insulated cavity construction — a 230mm AAC block inner leaf, a 120mm rockwool insulation cavity, and a 50mm brick outer leaf — achieving a whole-wall U-value of 0.11 W/m²K. The roof construction achieves U = 0.09 W/m²K through 250mm of polyiso insulation between and below the structural concrete slab. All windows are triple-glazed, thermally broken uPVC units with overall U-values of 0.75 W/m²K — the first residential use of such windows in Chandigarh, custom manufactured to our specification by a supplier in Ahmedabad.
The building's airtightness — measured at n50 = 0.42/h in the mandatory pre-handover blower door test — exceeds even the standard PHI certification requirement of 0.6/h, and is believed to be the best result ever recorded for a residential project in India. This exceptional airtightness was achieved through meticulous site supervision, a dedicated airtightness co-ordinator on-site throughout the construction programme, and the use of a Pro Clima airtight membrane and tape system throughout.
A whole-house MVHR unit — the Zehnder ComfoAir Q450 — provides continuous filtered fresh air at 94% heat recovery efficiency, maintaining exceptional indoor air quality without any heat loss. In summer, the system's built-in bypass mode allows direct night-time cool air flushing when outdoor temperatures fall below indoor temperatures — the primary passive cooling strategy during Chandigarh's shoulder seasons.
The remaining energy needs — primarily for lighting, appliances, and the home's single 5kW air-to-water heat pump that handles peak summer and winter periods — are met entirely by a 10kW rooftop solar PV array. The Malhotra family's first full year of occupancy recorded an average monthly electricity bill of ₹620 — against a code-compliant equivalent home's estimated ₹8,500 per month. The home is currently the subject of a post-occupancy monitoring study by IIT Roorkee's Building Energy Efficiency Research Group.
Challenge & Solution
What We Faced
Achieving PHI certification in North India's composite climate — hot and humid summers, cold winters, and extreme diurnal temperature swings in the shoulder seasons — required navigating a certification standard developed primarily for European climates and adapting it rigorously to Indian conditions. No local supply chain existed for several critical components: triple-glazed thermally broken windows, Pro Clima airtight membranes, and the MVHR unit all required importation from European manufacturers, with significant lead time, customs complexity, and cost implications. Local contractor teams had no prior experience with the airtight construction techniques that PHI certification demands.
How We Solved It
Our design team worked directly with the Passive House Institute in Darmstadt to <strong>adapt the PHPP energy modelling software</strong> for Chandigarh's specific climate data — a process that required three rounds of review and approval before the design target could be confirmed as achievable. The imported component challenge was managed through early procurement — all European components were ordered 14 months before their installation date, building in substantial buffer for customs delays. The contractor airtightness training challenge was addressed by <strong>running a three-day site workshop</strong> for the entire construction team before any envelope works began, led by a Pro Clima-certified airtightness trainer brought from Germany specifically for the project. The investment in training paid back many times over in the blower door test result.
"EcoBuild Studio transformed our vision into reality. The green villa exceeded all our expectations in both beauty and sustainability."
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