Five climate zones, five different homes

Editorial note. This article and the live tool linked from it are advisory commentary on climate-responsive residential design. The numerical bands shown — wall thicknesses, window sizes, roof slopes, overhang depths — are derived from ECBC 2017, Eco Niwas Samhita 2018, and supplementary sources, and are presented as a starting reference. They are not structural design values, and they do not replace your project's architect or RCC consultant. For any sanctioned construction drawing, the licensed professional on your project signs off on the final envelope.

The same builder ships the same wall section to five different climates. A 9-inch brick wall, a 100 mm RCC roof, identical window sizes, identical sill heights. Send that wall to Jaipur and the room runs noticeably hotter than the air outside on a May afternoon. Send it to Bangalore and the room is several degrees warmer than it could have been if the builder had read one chapter of one document.

That document is ECBC 2017 — the Energy Conservation Building Code — with the residential extension formalised as Eco Niwas Samhita 2018. Together they define five climate zones for India and discuss envelope responses for each. They are not paid documents. The information is free. Most builders have not read either.

This essay names the five zones, sketches what each zone asks of the home, and ends with a working tool that lets you compare envelopes city by city.

The five zones, named

ECBC 2017 divides India into five residential climate zones, defined by Köppen-Geiger classification and seasonal temperature/humidity bands.

A sixth and seventh zone — Tropical (Kerala / Andaman) and Extreme Rainfall (Cherrapunji, NE India) — sit outside the headline ECBC five and are commonly treated separately in vernacular architectural traditions and in supplementary climate tables. GrehYug's climate engine carries advisory bands for all seven so that a tool user in Kochi or Shillong is not reduced to a false default.

The four levers per zone

Climate-responsive design comes down to four envelope levers — the same four that ECBC and Eco Niwas Samhita discuss in their chapters on building envelope:

1. Window size and sill height by orientation
2. Wall thickness and insulation R-value
3. Roof slope (drainage and snow-shedding) and roof insulation
4. Overhang / chajja depth by face

A correctly specified envelope shifts a typical Indian residential thermal performance noticeably without active cooling — the exact delta depends on construction, occupancy, and orientation. An incorrectly specified envelope hands that delta back to the air-conditioner — and to the EB bill, every month, for fifty years.

Hot-Dry — the building wears thick walls and a hat

The Rajasthan haveli is not a styling decision. The thick external wall is a thermal-mass strategy: the wall absorbs the day's heat slowly and releases it overnight when the air is cooler. The deep jharokha on the south and west — the same balcony Mughal-era engineers cut into Jaipur's Hawa Mahal — is a fixed shading device.

A faithful Hot-Dry response approximates:

• External wall thicker than the standard 9" — high thermal mass; cavity walls or AAC blocks where modern construction permits.
• Windows small on west and high-silled on south; larger on north (where there is no direct-gain problem).
• Overhangs deep on south and west.
• Roof slope flat — rain is rare; thermal-mass roofs win.
• Courtyard essential — the aangan is a heat sink and a cool-air pump.

The home that ignores all of this is the home with three split ACs running through summer.

Warm-Humid — the building learns to breathe

Mumbai and Chennai do not need thick walls. They need air. The thermal problem is humidity above 70 %, and the only cheap thermodynamic answer is to move air across skin. Cross-ventilation is survival, not luxury.

A Warm-Humid response approximates:

• Standard 9" wall is fine — thermal mass is less useful when night-time temperatures stay warm.
• Windows large and operable on north and east (cool wind); shaded but generous on south; small on west.
• Verandah depth on every habitable face — it is the rain-and-sun buffer plus a breeze corridor.
• Roof slope steep — heavy monsoon rain shedding; tiled or sloped RCC.
• Plinth raised — flood and damp protection.

A high-rise apartment in Mumbai with sealed bay windows and floor-to-ceiling glass that does not open is a Warm-Humid failure. The rule book has been violated by the spec sheet.

Composite — the climate where Vastu was calibrated

Delhi, Lucknow, Bhopal, Patna — the Indo-Gangetic plain — see all four seasons in extremity: hot summers, cold winters, intense monsoons. This is the climate where classical Vastu was calibrated: the canonical "small west window, large north window" rules are tuned for exactly this band, where solar heat in May is a problem and solar warmth in January is a relief.

A Composite response approximates:

• External wall standard 9" with adequate insulation.
• Windows large on north (heat sink, daylight) and northeast; small on west; high-silled on south so winter sun penetrates and summer sun does not.
• Overhangs deep on south and west.
• Roof slope modest for monsoon shedding.
• Courtyard or central skylight essential — same reason as Hot-Dry.

This is also the zone where standard "follow Vastu" advice is least likely to lead the home wrong, because the rules and the climate were co-designed.

Temperate — the most forgiving, the most over-engineered

Bengaluru and Pune are the easy mode. Year-round mild temperatures, moderate humidity, gentle breeze. The envelope can be lighter, the window placement more flexible, the courtyard truly optional. And yet Bengaluru is full of buildings that import Delhi specifications wholesale: thick walls, deep overhangs, small west windows, when the climate would have allowed a generous north window and an open verandah.

A Temperate response approximates:

• External wall 9" is plenty.
• Windows generous on all faces.
• Overhangs modest.
• Roof slope moderate for the monsoon.
• Courtyard optional — the climate is breezy enough.

The over-engineering tax in Temperate climates is real. The building costs more, the rooms feel smaller, and the climate gave you nothing back. The brief should relax in this zone, not stiffen.

Cold — the climate that reverses Vastu

This is the zone where standard Vastu fails most explicitly. Classical texts forbid large south windows; in Srinagar and Shimla, south windows are the heating system. Passive solar gain in January is the difference between a room that is borderline liveable in winter and one that is not. The classical rule was calibrated for the plains; in the Himalayas, the orientation calculus inverts.

A Cold response approximates:

• External wall much thicker than the plains norm; double-glazing on glazed openings.
• Windows maximum on south (low sill — the heater of last resort), generous on east, minimum on north (cold drafts).
• Overhangs zero on south — winter sun must enter; the eaves are the rain/snow protection on the other faces.
• Roof slope steep for snow shedding.
• Plinth higher for frost.
• No courtyard — open courts bleed heat at night.
• Ceiling height lower — heat retention beats spaciousness.

Tell a Srinagar buyer that "Vastu says small south windows" and you have just specified a freezer.

Same plot, different city — the comparison demo

The argument we have been making is not that there are five zones, it is that the same generated plan must take five different shapes when the city changes. The component below is live: pick a city or enter a PIN code, and the envelope reference for that city is drawn from GrehYug's climate data set in real time.

This is what the difference looks like, drawn instead of asserted. A Mumbai home and a Jaipur home are not the same building with different paint. They are different envelopes solving different problems. The numbers shown are advisory bands for editorial reading — they are not structural design values, and your architect / RCC consultant signs off on the final envelope before any drawing is sanctioned.

How this shapes a GrehYug-generated plan

GrehYug's climate data set is consumed by the residential pipeline in two specific places:

1. In the Vastu Intelligence Report PDF, where the climate-zone description, recommended window orientations, and courtyard guidance are surfaced as advisory pages for the user.
2. In the floor-plan generator, where the climate engine informs door and window placement on the user-selected facing.

Wall thickness, roof slope, overhang depth, foundation, plinth, and structural specifications are not auto-generated by the floor-plan tool. Those decisions stay with your architect and RCC consultant, who must sign off on the final drawing before construction.

The output is not a generic 30 × 40 plan; it is a 30 × 40 plan with climate-aware opening sizes and an advisory envelope reference for the city you specified. The remainder of the climate response — the wall, the roof, the foundation — is articulated for your architect to apply, not signed by the tool.

For a deeper view, the live tool at /tools/climate-engineering lets you pick any of 80+ Indian cities (or enter a PIN code if your city is not on the list) and read the full envelope reference — windows, walls, roof, overhangs, courtyard guidance — drawn from ECBC 2017, Eco Niwas Samhita 2018, and supplementary climate tables.

Sources

1. Energy Conservation Building Code (ECBC) 2017, Bureau of Energy Efficiency, Government of India.
2. Eco Niwas Samhita 2018 — Energy Conservation Building Code for Residential Buildings, Bureau of Energy Efficiency.
3. NBC India 2016 (Bureau of Indian Standards), Part 8 — Building Services.
4. Köppen, W., Das geographische System der Klimate (Köppen-Geiger Handbuch der Klimatologie, 1936).
5. Manual of Tropical Housing and Building, Koenigsberger, Ingersoll, Mayhew, Szokolay — Longman, 1973.
6. Climate Responsive Architecture: A Design Handbook for Energy-Efficient Buildings, Krishan, Baker, Yannas, Szokolay — McGraw-Hill, 2001.
7. India Meteorological Department station data (1991–2020 normals) for cities cited.