Earth-friendly ways to keep your house cool (and the best air-con if you absolutely must)
The South African platteland isn’t a place for sissies in summer, considering that the mercury soars close to 50˚C in places like the Kalahari. Such temperatures can prevent you from sleeping at night and might even make you feel slightly unhinged – I once clambered into a fountain in the Oudtshoorn CBD, fully clothed. No, it wasn’t the spirit of the arts festival that made me lose my inhibitions, but the temperature that had risen to 46˚C.
Every region, from subtropical KwaZulu-Natal to the arid interior, offers its own challenges in the hot months. There are, however, universal principles you can apply to make your house liveable, whether you’re building, making structural alterations or buying an existing house. Cape Town architect Etienne Britz of Boukuns explains that the comfort of a house in different seasons depends on the design process as a whole, in which a number of aspects play a role. Unfortunately, the mere fact that a house faces north doesn’t mean you’ll enjoy living there in summer. Etienne explains that a northern orientation is rather about the fact that the largest openings in your house should face north.
“In arid areas such as the Karoo there should be a balance between the size and the number of windows and doors on the one hand and the thermal mass – the thickness and mass of the walls or roof – of the structure on the other hand.”
The cicadas are screeching, the dogs are looking as wilted as the garden, and at night you lie awake with a damp cloth on your forehead. Thankfully, you don’t have to rely on air conditioning to keep your house cool – there are alternative ways to make it liveable.
In layman’s terms, this would mean that, on warm days, the walls and roof absorb heat that then warms the house at night when the temperature cools down – architects call this the “thermal flywheel effect”. “This is the most effective way to regulate temperature in a green way. Just think of those wonderfully cool old farmhouses with their thick stone walls and only a few small windows.”
And then there is good old crossventilation (our grandpartents called it a “draught”), which makes the heat more bearable in subtropical areas such as KwaZulu-Natal.
“In arid areas one should be careful in the mornings of exchanging the cool air of the night for warmer air from outside,” Etienne says. “Not every room needs a window on each side; rather, it is important for the air to flow through
the whole house and find its way from the front door to the back door.”
Having larger windows or a greater number of them is not a solution either. “Glass is an exceptionally good conductor of heat – another reason why the old farmhouses had so few windows.” Shade from outside remains your best friend, and if you’re building from scratch, Etienne explains you should recess windows deep into the walls so that the sidewalls cast shadows on the glass. A solution for an existing house is a screen that prevents the sun from shining onto the glass. “A pergola in front of the northern windows makes a big difference in summer and will let sunlight through in winter as long as the pergola is the correct depth (1,2m for a window that is 2,3m from ground level).”
Cool construction choices
Remember the following when you buy or build a house, says Etienne:
• The roof material itself is not as important as the colour. White is a good choice, as it reflects light the best. • Insulation material inside the roof is essential, and it is required by national building regulations. There must be space between the roof tiles and the insulation material. A fibre blanket such as Aerolite works well, whereas metal foil placed directly on the ceiling simply gathers dust and will lose its effectiveness after a year.
• Your choice of flooring does play a role, but it should not be so light that it reflects sunlight and thus heats other elements in the house. Stone, concrete and tiled floors keep a house cooler than wood or carpeting does.
A stoep helps to keep a house cool provided the heat can escape via a high opening or semi-solid roof such as a trellis. The dark-red paint or slate tiles you see on old farmhouse stoeps ensure the floor doesn’t reflect heat into the house.
• Tropical climates Timber-frame houses (a sustainable building method) work well because they breathe, in a manner of speaking. • Arid regions Brick or stone are your best choices, because they’re relatively affordable and have thermal mass, especially if you build a cavity wall (a “double wall” that consists of two layers of brick or stone separated by a 50mm cavity). • Eco-conscious options Use a variety of building materials, such as a stone wall with insulation and timber cladding on the inside. This will make it far easier to get by without air conditioning. • Adventurously eco-aware Build walls from rammed earth. Soil from the area is combined with cement and rammed in layers, more or less as you would cast a concrete wall. The thermal mass of these walls is ideal for arid regions. Because they’re made from the very earth they’re standing on, it’s as though the building is growing out of the landscape.
You won’t find a better “screen” than a tree, says Cape Town landscaper Petro Jacobs, but consider all four seasons before you start planting. “It’s not only the size, shape and root system that are important. Trees and shrubs should also be planted in such a way that they contribute to good natural ventilation. They’re often grouped too close together and, over the years, can become entangled, affecting the flow of air.” • Chill the northern side “Deciduous trees are my favourites [see left], as they let you witness the change of the seasons and allow the sun through in winter,” Petro says. >
• Cool down a hot wall Sometimes it isn’t the sun that heats a room but a wall that reflects heat towards the house. Petro solves this problem by planting a creeping fig ( Ficus pumila). The false olive ( Buddleja saligna) works well when you want to create an indigenous hedge against a wall. • Pergola to the rescue If you choose to follow Etienne’s advice and make use of a pergola on the northern side, Petro suggests you plant a deciduous creeper such as wisteria, which will let sunlight through in winter. “Edible creepers like a granadilla are popular, but this is an evergreen plant that won’t let much sunlight through. If you’d like a fragrant plant, I’d suggest star jasmine ( Trachelospermum jasminoides), which flowers in summer. Keep in mind, though, that it may cause hayfever.”
Etienne Britz boukuns.co.za Petro Jacobs petrolandscaping.co.za