As Nepal heats up with Terai cities baking at 40°C plus and Kathmandu getting hotter summers poor city dwellers feel the heat (Jagan Chapagain, 2024). Even in cramped slums or narrow alleys, small brick houses become ovens during summer. Air conditioning, however, is not possible or too expensive for most. Instead, planners and architects are returning to age-old passive cooling techniques to keep people comfortable without electricity. Drawing inspiration from Nepal’s traditional wisdom and global examples, designers focus on building orientation, ventilation, shade, mass, vegetation, and smart community design. Such measures can bring indoor temperatures down by several degrees (US Department of Energy, 2023), cutting energy consumption and health risks simultaneously.
Design for Breezes: Shape and Orientation
Where and how you orient your building does make all the difference. In Nepal’s sunny plains and hills, the trick is intercepting prevailing breezes and shade out direct sun. Architects orient long facades on the east-west axis to present narrow ends to the low-angle morning and evening sun, and longer north-south walls get sunlight without excess heat. South or southeast-oriented windows are recessed or reduced. For example, a government school at Hetauda was oriented south and southeast for daylight but built with a wide 1.2m roof overhang; the deep cantilever completely shields the southern wall from direct sun (ENERGY EFFICIENT AND PASSIVE BUILDING DESIGN MANUAL FOR GOVERNMENT BUILDINGS IN NEPAL, n.d.).
Passive strategies like windows facing one another create efficient cross-ventilation that forces heat out. Tall ceilings and roof vents are stack ventilators that suck hot air upward and out. In a Nepali school building the architects included clerestory windows and steep multi-story roofs to let warm air rise above students’ heads. These high north walls and multiple openings mirror strategies employed in other hot climates (Lessons from Sustainable and Vernacular Passive Cooling Strategies Used in Traditional Iranian Houses, 2021), illustrating the way design substitutes fans.
Ventilation and Airflow: Permit Air to Circulate
Compact city blocks retain heat, and planners therefore focus beyond the size of the individual dwelling to the neighborhood scale. Planning ventilation corridors, parallel parks, water bodies or open spaces can channel cooling breezes deep into cities. Even the inclusion of small open courtyards or lanes between buildings can break up urban heat islands. Inside a house or tenement, high on one wall and low on the other wall placement of windows or screened openings encourages strong breeze through the building. In Nepalgunj, the occupants of houses retrofitted for cross-ventilation said they felt much cooler indoors and suffered from fewer symptoms of heat stress (Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background, n.d.).
Inside buildings, widespread use of open plans and semi-open areas (e.g. verandas or chautaris) provide ventilation room for air to circulate. Details like solar chimneys enhance stack ventilation, tall, vented towers heated on the sunny side draw air upward. Nepalese architects, for example, commonly include passive chimneys (5-6m high) that create a night-time draft. In one Hetauda project, 18-foot chimneys collected solar heat by day and functioned as active draft vents at night, significantly improving airflow (ENERGY EFFICIENT AND PASSIVE BUILDING DESIGN MANUAL FOR GOVERNMENT BUILDINGS IN NEPAL, n.d.). Such simple modifications can cool indoor air by a degree or two on their own.
Shading and Reflective Surfaces: Blocking the Sun
Regardless of how well-ventilated a building might be, you first need to reduce heat gain. Steep roof overhangs, awnings, pergolas, and lattice screens act to intercept sunlight before it hits walls and windows. Nepalese vernacular buildings have broad eaves, for instance, Newari carved wood shopfronts and Bhutanese-style verandahs, that just shade the facade. Even the addition of bamboo blinds or cloth screens to sunny house facades can intercept the sun’s hottest rays. Vines and trees planted near a house create free, living shade, the leaf canopy cools the air around and over the house. Research shows that a simple tree canopy can bring indoor temperatures substantially down by blocking the direct sun(Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background, n.d.).
Roof treatments are another low-cost measure. Painting a metal or concrete roof white (a cool roof) dramatically boosts reflectance. In trials, cool roof coatings on Nepalese houses reduced interior temperatures by about 2-5°C (@kathmandupost, 2025). Similarly, a U.S. Department of Energy study indicated that, on a hot afternoon, a reflective roof can be about 28°C cooler than an untreated roof (US Department of Energy, 2023). It is similar to wearing a white shirt in the sun instead of a black one, the surface gets much less heat. Cool roofs are inexpensive, reflective ceramic tiles or lime white paint get the job done. Indeed, Telangana in India recently required cool roofs for new buildings (@kathmandupost, 2025), a move that could be emulated by Nepal. Street surfaces can be cooled too, light-colored pavement and water elements (e.g. fountains or reflecting pools) resist ambient heat by reflecting sunlight and adding evaporative cooling. Shading and reflective finishes are the first line of defense against heat gain, period.
Walls That Breathe: Thermal Mass and Materials
Earth-thick construction is the other major one. Nepali traditional houses use materials like mud, brick, stone, and wood which naturally control heat. Thick walls warm up slowly and release heat slowly, smoothing out temperature fluctuations. Field measurements in the subtropics of Nepal showed that a bedroom in a mud/brick house could stay ~4.6°C cooler than the outside air by day (Rijal, 2018). Nevertheless, one piece of climate research found that houses with mud floors, thatched roofs, and mud walls are effective at reducing indoor air temperatures (Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background, n.d.). Indeed, a stone wall finished with 10cm mud plaster (a common rural building) can make interiors comfortable on hot days. Stone masonry is well thermally if accompanied by a mud plaster surface finish, it’s comfortable in both extreme seasons. Traditional stone and mud buildings naturally absorb heat.
In modern construction, these lessons inform choices too. Rammed earth or compressed earth blocks are gaining traction in reconstruction, they are high mass and inexpensive. Plain mud plaster for walls not only uses local waste earth but also allows moisture to breathe, forestalling indoor bursts of dampness. Mud plasters are famous for being less toxic and energy-intensive yet water-resistant. A porous earthen wall will absorb daytime heat and radiate it after dark. To assist on warmer nights, designers then open windows to flush out stored heat. In Nepal’s mid-hills (Kathmandu Valley), some retrofits add thin applications of insulation or even vacuum insulation panels beneath the roof to slow heat entry in summer while holding on to heat in winter. Even lime mortar and brick (rather than concrete) can make a huge difference to thermal comfort, it’s all about maximizing inertia against the heat.
Green Cover and Nature Based Cooling
Land is scarce in a city, but small green patches do make a difference. Roof gardens and wall plants are air conditioners. A green roof, layers of plants, and soil can cool the rooftop surface by dozens of degrees and cut peak indoor heat by up to 15°C in experiments (Jia et al., 2024). In practice, villagers in Pokhara and Patan are experimenting with potted plants on terraces and drip-irrigated rooftop gardens for vegetables. Plants shade the roof membrane and cool through evapotranspiration (similar to plants perspiring). Similarly, planting alleys and courtyards with trees and shrubs (local species like ficus, neem, or lokta) cool ground-level microclimates. Even small water bodies, a small pond or fountain in a courtyard, cause evaporative cooling. On a larger scale, city parks and riverside green belts become urban lungs that moderate ambient heat island effects.
Green and reflective cool measures complement each other, as DOE research shows that green roofs insulate using plants, while cool roofs reflect (Jia et al., 2024). Combined, they cut significantly the cooling energy needed. On larger spatial scales than individual homes, nature-based urban planning, like street trees and permeable surfaces, and city parks, can channel breeze and lower neighborhood temperature. Kathmandu’s rat race has little green space, but visionary plans (e.g. planned Kathmandu Valley climate adaptation plans) are beginning to prioritize urban forests and roadside planting as a primary heat defense.
Community Design: Density and Courtyards
Passive cooling in crowded city settlements also requires rethinking the layout of clusters of buildings. Nepali and Newari settlements in the past already had central courtyards and stair-step spacing among houses to allow air and light to enter. Such courtyards, maybe planted or paved with light-colored stones, are cool social spaces where heat has a chance to rise and morning sunlight is reduced. The common open space also means additional perimeter walls, so additional facades can be shaded and ventilated. As one study of Kathmandu’s Newari houses suggests, these courtyard houses prioritize environmental control through passive cooling techniques and economy of space (Bhattarai and Shrestha, 2024). In modern-day slums, architects are experimenting with adding small inner courtyards or turning alleyways into open spaces to break rows of tin huts.
On a larger scale, planners talk of ventilation corridors, bands of green or blue (trees, parks, or rivers) through a neighborhood to direct air. For example, the Nepalgunj resilience plan explicitly recommends the creation of blue-green corridors to introduce cool breezes into the city center (Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background, n.d.). On the ground, that could mean retaining an avenue of mature trees along a street, or designing riverfront promenades so river breeze spills out into surrounding blocks. Orientation of whole streets can also put summer winds in line with building edges that are shaded. Collective action works too, collective choice to plant street trees, whitewash roofs, or arrange multi-story blocks with shared terraces can have disproportionate cooling effects.
Lessons from abroad and from tradition
Nepal’s native architecture is inspiring enough. Hillside village houses in rural areas prefer a south-facing orientation to catch winter sun and use thick insulation, the reverse of tropical needs, but even here architects can take up that principle of seasonal responsiveness. In the Terai, stilts beneath rural huts allow air below the floor, cooling houses in hot, humid summers. Inland, thatch, and bamboo roofs (common in Dhading or Mugu) are great heat insulation but are being replaced by metal sheets; reviving green roofs of grass or even sedum mats could duplicate that cooling at little cost.
Global precedents uphold these principles. Iranian desert village architects designed high, shaded wind walls and utilized evaporative pools in courtyards to cool houses (Lessons from Sustainable and Vernacular Passive Cooling Strategies Used in Traditional Iranian Houses, 2021), solutions that Nepal’s dry Zone could adopt (consider small roof water ponds). Jakarta or Surabaya coastal cities use open lattices and cross-ventilated facades to cool skyscrapers; the same can be applied to Kathmandu’s mid-rise complexes. African city cool roof projects (whitewashing mud huts) and Singapore’s ubiquitous sky gardens prove that greenery anywhere, even on balconies, is worth it. In all cases, the principle is the same, use building form and nature to design a microclimate that reduces peak heat.
Adapting to Nepal’s Climate Zones
Nepal’s microclimates vary; hot Terai plains, monsoonal mid-hills, and cold Himalayas. Passive cooling strategies must be attuned to each. In hot, wet terai, ventilate maximally, houses there may employ high ceilings, wide eaves, and screened windows (to exclude mosquitoes) to encourage hot air to rise and exterior shape breezes to enter. Light walls and metal roofs (typically corrugated GI sheets) must be shaded or painted to reflect sunlight. In Kathmandu and mid-hills (warm summer, cold winter), a hybrid strategy is effective, insulation is provided by thick walls of bricks and mud floors, and moveable shading like retractable awnings, shutters tackle daytime sun, roofs receive added winter warmth insulation. Many Newari Valley houses face south or westward to collect winter sun, but slight changes such as awning those windows, adding upper vents, or planting monsoon-resistant vines suffice to cool them in summer. Mountain villages can, however, use passive solar design like large south windows for winter warmth, but still benefit from having shaded north walls. An architect who is knowledgeable about Nepali tradition can then marry vernacular knowledge to passive cooling like rammed-earth building (common in Kavre rebuilds) moderates heat and cold naturally.
Challenges and Low-Cost Innovations
Passive cooling in dense poor conditions is difficult. Space is at a premium, how to have trees or courtyards where every square meter counts? Funds are lacking, and the integration of ventilation design or special materials must be affordable. Developers and residents in many of these areas may not be aware of such ideas. Elimination of these requires innovation and community mobilization. For instance, a slum has no front gardens, but neighbors can share roof space, the conversion of flat terraces to shared green roofs or whitewashing them is cheap and serves all below. Local government and NGOs can facilitate a pilot project that could subsidize cool coating for cheap metal roofs in flood-risk terai towns. Simple design requirements, for example, the provision of 50 cm eaves and cross-ventilation in new housing clusters, could be cheap but effective building controls.
Architects can promote passive solutions to clients in workshops and meetings, supported by evidence and examples of the benefits. Many of the interventions repay themselves within a limited timeframe, a study in Nepal revealed that without air conditioning, passive measures cooled classrooms by approximately 2-6°C (Shrestha and Rijal, 2023), with potential concentration and health benefits. Heat-coping training through radio or local community leaders (on sleeping on cool floors or drying clothes in sun-obstructed rooms) supports design. Maintenance is also an issue, urban trees need watering and pruning, and mud plaster walls need repairing after rain. But these are possible locally with limited training (as volunteer schemes in Nepal are already demonstrated with rammed-earth projects).
Even in tight spaces, inexpensive solutions add up. The cents to place a reflective foil or second coat under tin roofs can save heat. It costs nearly nothing but adds thermal mass to use brick or compressed earth blocks (often obtainable from a local kiln) for walls, instead of concrete. The long-term goal is practical innovation, combining vernacular solutions (e.g. bamboo trellis, courtyards) with small modern upgrades (paint, vents, solar-cell-powered fans) to make life livable.
Conclusion
For architects working in Nepal’s expanding cities, air conditioning is not an option, not even an option for poor households. Rather, the passive design kit offers tested, low-energy solutions to cooling buildings and occupants safely (Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background, n.d.). Through building orientation to sun and wind, natural ventilation design, shading facades, employing heavy local materials, and green roofs and streets, architects can reduce indoor heat substantially even in the most dense slums. Doing these steps is about embracing Nepal’s climatic diversity and architectural heritage, each courtyard, tree, and cool roof takes us closer to city resilience. The payoff is huge, increased comfort, reduced illnesses, and a city that is still livable under the heat.
References:
- Jagan Chapagain (2024). Learning from Nepal: Coping with hotter and longer heatwaves. [online] World Economic Forum. Available at: https://www.weforum.org/stories/2024/06/nepal-kathmandu-heatwave-us-europe-red-cross/ [Accessed 18 Jun. 2025].
- US Department of Energy (2023). Cool Roofs. [online] Energy.gov. Available at: https://www.energy.gov/energysaver/cool-roofs.
- ENERGY EFFICIENT AND PASSIVE BUILDING DESIGN MANUAL FOR GOVERNMENT BUILDINGS IN NEPAL. (n.d.). Available at: https://giwmscdntwo.gov.np/media/pdf_upload/3._ENERGY_EFFICIENT_AND_PASSIVE_BUILDING_DESIGN_MANUAL_FOR_GOVERNMENT_BUILDINGS_IN_NEPAL.docx.pdf.
- Lessons from Sustainable and Vernacular Passive Cooling Strategies Used in Traditional Iranian Houses. (2021). Journal of Sustainability Research, 3(3). doi:https://doi.org/10.20900/jsr20210014.
- Reducing Heat Impacts in Nepalgunj City, Nepal POLICY BRIEF Background. (n.d.). Available at: https://southasia.iclei.org/wp-content/uploads/2022/03/RCCC-Policy-Brief-Nepalgunj-Nepal.pdf [Accessed 19 Jun. 2025].
- @kathmandupost. (2025). How to make homes cooler. [online] Available at: https://kathmandupost.com/columns/2025/06/10/how-to-make-homes-cooler [Accessed 19 Jun. 2025].
- Rijal, H.B. (2018). Passive Cooling of the Traditional Houses of Nepal. Sustainable Houses and Living in the Hot-Humid Climates of Asia, [online] pp.397–406. doi:https://doi.org/10.1007/978-981-10-8465-2_38.
- Jia, S., Weng, Q., Yoo, C., Xiao, H. and Zhong, Q. (2024). Building energy savings by green roofs and cool roofs in current and future climates. npj urban sustainability, 4(1). doi:https://doi.org/10.1038/s42949-024-00159-8.
- Bhattarai, K. and Shrestha, S. (2024). Sustainable Design and Cultural Preservation in Newari Architecture. International Journal of Research Publication and Reviews, 5(9), pp.1797–1805. doi:https://doi.org/10.55248/gengpi.5.0924.2610.
- Shrestha, M. and Rijal, H.B. (2023). Investigation on Summer Thermal Comfort and Passive Thermal Improvements in Naturally Ventilated Nepalese School Buildings. Energies, 16(3), p.1251. doi:https://doi.org/10.3390/en16031251.
