London, Sep 10 (The Conversation) During a seminar in the late 1990s discussing building cooling strategies, I distinctly remember hearing the prediction that “in 30 years' time, the climate of London will feel like Marseille’s today.” That warning has stayed with me ever since. Back then, the prospect was both alarming and somewhat intriguingly attractive.
Now, three decades later, it's all become very real. As someone with Mediterranean roots living in London, I've experienced this climate transition firsthand. When I co-authored "The Architecture of Natural Cooling," I drew from both professional expertise and childhood memories of whitewashed walls, shady courtyards, and shuttered windows.
These age-old techniques, well-adapted to the Mediterranean, now offer valuable insights for modern Britain, where heatwaves have become routine.
One of the simplest yet most effective methods for cooling buildings is changing their colour. White surfaces have the ability to reflect sunlight rather than absorb it. Research indicates that painting roofs white or applying reflective coatings can potentially lower indoor temperatures by over 1°C and even by more than 4°C in some cases. Additionally, these measures can reduce outdoor air temperatures by up to 2°C.
While these temperature changes might seem modest, on a city-wide scale, they can significantly mitigate the urban heat island effect, where urban surfaces absorb heat, making cities warmer than the surrounding rural areas, thereby keeping homes more comfortable during the peak heat of the day.
The effectiveness of these strategies, however, comes with a stipulation. The more we incorporate low-energy “passive” strategies—such as using shutters, painting buildings white, and enhancing ventilation—the better they work. For instance, a white roof is more effective when windows remain closed during the hottest periods, with shutters or external shades blocking the sun.
Moreover, closing windows is complemented by heavyweight walls and floors, as these materials retain the coolness of night air and gradually release it during the day. This is why Mediterranean homes can remain comfortable for extended periods, even during extreme heat.
Night-time ventilation also holds importance—provided that outdoor temperatures actually drop after dark. In cities like London or Manchester, where the urban heat island effect prevails, adopting reflective roofs and minimizing waste heat from air-conditioning units is even more essential.
What about winter concerns? Some might worry that a white roof would make their homes colder during winter. However, this issue is relatively minor, especially if the roof is adequately insulated. The key factor for winter heating is the ability of a home's outer shell to retain internal heat, rather than preventing external heat entry.
In northern climates with weak winter sunlight often obscured by clouds, harnessing solar energy for warmth is more effectively achieved through allowing sunlight to enter via double-glazed windows than relying on darker construction materials.
Repainting a home white is not prohibitively expensive, especially when compared to the overall costs of heating and maintaining a house. Many homeowners in the UK, particularly those in suburban areas, already opt for white finishes during refurbishments.
For flat or low-pitched roofs, applying reflective coatings is relatively cost-effective. However, for steeply pitched roofs, paint may not be a viable option due to wear and aesthetics, as frequent repainting would be required. Tile roofs, in particular, need to “breathe” to let moisture out, and paint could impede this, causing damp issues.
The optimal choice is to replace dark shingles or slate tiles with more reflective clay tiles that lower the roof's surface temperature. While this is a more time-consuming and costly solution, it can be worthwhile, with costs in the UK starting from around GBP 125 per square meter of roofing.
The climate is undeniably changing, but sometimes the best solutions are neither high-tech nor expensive.
A coat of white paint, together with a few simple design strategies, could help make Britain’s homes cooler, less expensive to operate, and better equipped for future climate changes and rising energy costs. (The Conversation) SKS SCY SCY
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