passive home cooling

Cooling the house without air conditioning, just using shading strategies, natural ventilation and adequate construction materials - that's the goal of passive home cooling.

Some passive cooling techniques may collide with others or collide with the landscape and site particulars or with some specific local conditions, but they remain a valid reference frame that we all should pay attention to.

Instruments and strategies

Passive cooling techniques are basically a set of instruments and strategies for hot climates and new buildings. They include:

- low thermal materials
- reflective materials;
- overhangs;
- natural ventilation strategies (largely based on windows and skylights)
- shading strategies.

Shading strategies & Trees

Shading is crucial in any passive cooling strategy. The more shaded a building is - especially the windows and the roof - the better.

The best shading is accomplished outside the building, and trees (deciduous trees in most cases) are usually the best mean to attain it. See for more details: Shading and trees.

The use of trees depends a lot on the particularities of each climate. In cold or temperate climates, do not use evergreen trees too close to the building. Instead, use deciduous trees on west and east side of home to reduce summer heat, and also, in most cases, in the sunnier side of the home (south in the northern hemisphere; north in the southern hemisphere).

Other Shading Strategies

Shading strategies may also include:

- some parts of the house or even other buildings: one part of the building may shade another part …
- overhangs, arbors, screens, awnings;
- interior shading through blinds, drapes and other interior devices (Note: this shading isn’t as effective as exterior shading).

Shading & overhangs

Overhangs are also a very effective passive solar cooling mean, in most climates: properly dimensioned they will block most of the sun and its unwanted heat during the summer months, when the sun is higher in the sky.

See, for details: Shading & Overhangs

Thermal mass and cooling

Materials used in walls, floor and other sun-exposed parts of the house should have adequate thermal storage or reflectance, that is, thermal properties able to respond to the needs of the climate where the building is located.

In cold climates the capacity of quickly absorbing solar heat and the capacity of providing a slow release of stored heat during the night, can be important when choosing constructions materials: masonry and stone for floors, walls, and roofs are materials that pose that issue. In other words: in cold climates, passive heating demands high thermal mass materials.

Obviously, passive cooling techniques demand mostly low thermal mass materials...

Low thermal mass materials

Low thermal mass walls and structures are a very common option in hot-humid climates with high nighttime temperatures.

Materials like metals and wood have that low thermal mass and are adequate to passive cooling techniques. Metal roofs and wood frames are very common in passive cooling precisely because they don’t heat well and cool quickly, when the sun disappears.

Reflective exterior surfaces

The use of highly reflective exterior surfaces is also advantageous and crucial in passive cooling, due to the large amount of the sun's heat that can be reflected away by reflection. Reflective roofing is particularly effective.

Color and texture are also important in this case. White or close-to-white colors are good options for reflectance. Shinier and smoother materials are also good options, since they are more reflective.

High mass materials for hot dry climates with cold nights

The use of high mass materials - materials that hold heat well and cool slowly, like masonry and stone for roofs, floors or walls - are adequate in hot dry climates, with cold or relatively cold nighttime temperatures.

Recent studies also show that high thermal mass elements can be used with advantage either in temperate climates and some hot climates. Low thermal mass materials aren’t the only solution.

Natural ventilation

In hot and humid tropical climates, with small day/night temperature amplitude, natural ventilation isn’t a good option. But in most other cases natural ventilation is an excellent passive cooling technique.

Obviously it demands a correct location of the windows, and a proper orientation of the building (which in some cases may collide with other solar heating or cooling strategies).

The windows design (double-hung and casement windows) and placement, as well as the shape and orientation of the building are crucial for natural ventilation strategies.

See, for details: Natural and mechanical ventilation and Types of windows