In part 4 of passive cooling or natural cooling, we will look at things that will involve more work and cost. If you are not doing major renovation on your house, these 2 ideas may not be that practical. Anyway, I’ll share what is possible should you choose to implement them.
Increase the roof overhang
The common roof overhang is around 1.5 to 2 feet. The roof overhangs shields the walls from direct sun as the sun gets higher in the sky. If you increase the overhang to 3 feet or more, then a larger portion of your wall will be shielded from direct sunlight. Many houses in Malaysia today are designed to look sleek and modern. In some designs, there is practically no overhang at all at the side and back walls. While these houses look nice, in hot whether, you are forced to use the air conditioner. Not only do the roof overhang shields the sun, it also helps protects to wall from rain, thus your paint will last longer. For the house above in the photo, although the windows are set in and somewhat shielded from direct sun, the walls are not.
For an existing house, extending the overhang will require a lot of modification. Instead, it will be better to install awnings. If you are building a house from ground up or if you are changing your roof trusses, then this may be something for you and your architect to consider.
Autoclaved Aerated Concrete blocks
Autoclaved aerated concrete (AAC) blocks are blocks that have many tiny air bubbles in them. Such blocks are used in place of clay or cement bricks. They are lighter and usually larger than bricks. They have much better heat insulation properties compared to concrete or clay brick walls due to the air trapped within.
When the blocks are cut, the structure within looks exactly like a sponge but is stiff and hard. The honeycomb structure results in a light and strong block that can support certain amount of weight. Autoclaved aerated concrete is not new technology. It was invented in the mid 1920s by Swedish architect and inventor Johan Axel Eriksson. It is used in precast construction. Although the use in normal houses are not widespread, it is gaining popularity. They have been used in several construction of high rise condominiums, commercial buildings as well as bungalows in Malaysia. Due to their lightweight nature, construction using these blocks is faster. The walls may also require less finishing since the surface is fairly smooth. Other names for AAC include safecrete, aircrete, lightcrete and others.
Some home builders have claimed significantly cooler home compared to those using the normal building material. Although they do not have figures to substantiate their claims, I believe there will be significant reduction in cooling requirement for your home. Overseas in cooler climate, there are reports that houses built with such blocks do not require additional insulation either to keep heat in during the winter or to keep the heat out during summer. Previous articles on passive cooling Part 1, Part 2 and Part 3