Climate-responsive design: principles and strategies by climate

How climate affects building design

A building constantly exchanges heat with its surroundings. It gains heat from the sun and warm air, loses it to cold air and wind, and its occupants feel the humidity and air movement indoors. Climate-responsive design uses the building itself, its form, orientation, openings, shading and materials, to manage those exchanges before mechanical systems are added.

Givoni's building bioclimatic chart is one tool for this. The local temperature and humidity are plotted on a psychrometric chart, with boundaries showing where daytime comfort ventilation, thermal mass with or without night ventilation, and direct or indirect evaporative cooling can keep the interior comfortable. The chart is based on expected indoor temperatures rather than outdoor ones, because a well-designed heavy building in a hot, dry region can stay well below the outdoor maximum: Givoni gives up to about 7 to 8 K, especially with night ventilation.

Principles that apply in every climate

• Read the climate first: classify it, then look at hourly and seasonal patterns of sun, wind, temperature and humidity rather than annual averages.
• Orient for the sun. Outside the tropics the midday sun is to the south in the northern hemisphere and to the north in the southern hemisphere, and its height at noon depends on latitude and season. The equator-facing facade is therefore the easiest to shade in summer and to open to the sun in winter, while east and west facades take morning and evening sun at low angles, which horizontal overhangs do little to block.
• Stop the sun before it reaches the glass. In the US Department of Energy's passive solar guidance, roof overhangs or trees shade the windows in summer, while the lower winter sun still reaches them.
• Use air movement deliberately. Givoni distinguishes comfort ventilation, which raises indoor air speed and helps only when the outdoor air is itself acceptable, from night ventilation, which cools the structure so it absorbs heat the next day.
• Match the thermal mass to the daily temperature swing. Mass evens out indoor temperatures, which helps most when nights are much cooler than days.
• Control the envelope. Where heating or cooling dominates, insulation and airtightness cut heat flow through walls, roofs and gaps; Natural Resources Canada notes that tightening an envelope raises indoor humidity, so controlled ventilation has to come with it.

Hot-dry climates (Köppen BWh and BSh)

Hot deserts and steppes have strong sun, low humidity and a large difference between day and night. Givoni notes that the outdoor daily range grows as humidity falls, and that the potential of night ventilation to lower indoor daytime temperatures is proportional to that range.

• Heavy, well-insulated and shaded construction, closed during the day and ventilated at night. For such a building Givoni puts the indoor maximum about 45 to 55% of the outdoor daily range below the outdoor maximum, and separately estimates about 6 to 8 K below it for a summer range of 15 to 20 K.
• Night ventilation alone works mainly where the daily maximum stays below about 36 °C. Above that, Givoni recommends adding evaporative cooling or air conditioning for the hottest hours.
• Direct evaporative cooling lowers the air temperature by about 70 to 80% of the wet-bulb depression, so it suits dry air. It adds moisture to the air and needs high airflow.
• Limit and shade the glazing, and use light-coloured surfaces, which the Department of Energy notes reflect incoming solar heat.

Hot-humid climates (Köppen A, and humid summers elsewhere)

Tropical climates, where even the coldest month averages at least 18 °C, and humid summers elsewhere combine heat with high humidity and a small difference between day and night. With little night coolness to store, thermal mass helps less, and shade and air movement come first.

• Cross-ventilate the occupied spaces. Givoni's comfort ventilation boundaries assume an indoor air speed of about 2 m/s, and the strategy works only when comfort is possible at the outdoor temperature, because a cross-ventilated interior follows the outdoor air temperature closely.
• In lightweight, naturally ventilated buildings indoor temperatures stay close to outdoor ones: Givoni notes that an outdoor-based bioclimatic chart is a reasonable guide for such buildings in humid regions.
• Shade glazing, walls and outdoor living spaces, and open the plan towards the prevailing breezes shown by the site's wind rose.
• Do not count on evaporative cooling: it depends on a large gap between the dry-bulb and wet-bulb temperatures, which humid air does not have.

Temperate and cold climates (Köppen C and D)

In temperate climates heating and cooling both matter and trade places with the seasons; in cold climates heating dominates. In the Köppen-Geiger definitions used by Beck and colleagues, temperate climates have a coldest month between 0 and 18 °C, and cold climates a coldest month at or below 0 °C, both with a warmest month above 10 °C.

• Let the winter sun in. The Department of Energy's passive solar guidance places the main windows within 30 degrees of true south, unshaded from 9 a.m. to 3 p.m. in winter; in the southern hemisphere the equivalent is true north. In colder climates it reduces the window area on the other facades while keeping adequate daylight.
• Store the gains. Floors and walls with thermal mass in the path of the sun absorb its heat and release it later; the Department of Energy notes they are particularly useful for heating in colder climates.
• Keep the heat in. Natural Resources Canada calls air leakage control the single most important retrofit activity, and pairs it with controlled whole-house ventilation to manage the humidity that builds up in a tighter house.
• In temperate climates, switch strategies by season: open to the sun and closed to cold winds in winter, shaded and ventilated in summer.

Design for the climate the building will live through

Climate-responsive design has to aim at a moving target. The IPCC reports that hot extremes, including heatwaves, have become more frequent and more intense across most land regions since the 1950s, and that every additional 0.5 °C of global warming brings clearly discernible increases in hot extremes and heavy precipitation.

Climate zones are moving too. Beck and colleagues (2023) project that between 1991–2020 and 2071–2099, 5% of the global land surface will change major Köppen-Geiger class under SSP1-2.6, 8% under SSP2-4.5 and 13% under SSP5-8.5. Test shading, ventilation and overheating against a future weather file as well as a typical one, and check that passive cooling still works: Givoni's limit for night ventilation alone, a daily maximum of about 36 °C, may be exceeded more often in a warmer climate.