Heat Gain

The outside weather temperature under the trees in the tropical hot and humid climate is better than you think. If an indoor environment feels unpleasant, it may be that the building design is to blame.

Building material absorbs heat, stores heat (thermal mass), and releases heat from the direct sunlight into both the interior and exterior of the building.

Heat can then be conducted through the air and reach our bodies.

The duration of a building material being allowed to be exposed to the sun is an important factor in determining heat gain of both interior and exterior environments.  

As a simple rule to prevent solar heat from conducting through the building material and releasing heat into the interior, avoid sunlight directly contacting the building material, usually the roof and the wall. 

A few examples of intervention include the double-roof, big leafy plants or a good-sized canopy tree shading, a cavity wall, or a cavity roof. 

Consider thermal mass, conductivity, and density

If a double-wall or double-roof is unachievable, you need a suitable building material that conducts, stores, and releases the right amount of heat at the right time.

Evangelisti, Luca & Battista, Gabriele & Guattari, Claudia & Basilicata, Carmine & De Lieto Vollaro, Roberto. (2014). Analysis of Two Models for Evaluating the Energy Performance of Different Buildings. Sustainability. 6. 5311-5321. 10.3390/su6085311.

Compare concrete, clay, steel, air, water, and timber. Water and air were brought into context as they assist a better understanding of the whole picture of the subject.

Relatively, concrete has high thermal mass, but low conductivity, and high density. 

Timber has high thermal mass, low conductivity, but low density. 

Clay has high thermal mass but lower than concrete, higher conductivity, and high density. 

Steel has a very high thermal mass, very high conductivity, and very high density. 

Air has high thermal mass, low conductivity, and very low density. Water has the highest thermal mass, but very low conductivity, and high density.

Put in simpler relative terms: 

When solar heat on the materials, 

Concrete - Feels cooling, interior only gets warm after some time, but heat stores in concrete for a long time and releases when the surrounding temperature is cooler (i.e., nighttime) 

Timber - Feels cooling for a while, but due to low density, the interior can immediately feel warm, and will not store heat for long

Clay - Feels cooling for a while, interior starts to feel warm after a while, stores heat but not as long as concrete, cools down faster

Steel - Feels immediately warm, the interior feels warm after a while, will store heat for a very long time

Air - Feels cooling, starts feeling warm after a long time, and will store heat for some time

Water - Feels cooling for a very long time, only starts feeling warm after a very long time, stores heat for a very long time

Of course, the above consideration does not consider air movement(wind). Air movement will carry the heat or the coldness released by the materials away.

 Design will determine the effect of heat gain on your comfort and the use of spaces.