UK residents are increasingly searching for ways to keep their homes cool as temperatures rise, with research indicating that over 4 million homes now have air conditioning. This figure has doubled since three years ago, though many homeowners hesitate to install the expensive units, which are often used for only a few weeks annually. While electric fans can provide temporary relief, they sometimes circulate warm air. The concept of window stacking offers a different approach to maintaining a comfortable indoor environment without the high costs of permanent cooling systems.
Anthony Threlfall, head of marketing at Everest, describes window stacking as a method of layering different types of window coverings, usually around three. This creates a combined system that blocks heat, controls light, and improves comfort during hot weather. Rather than relying on a single blind or curtain, the method builds up a heat-blocking layer, a light-diffusing layer, and a heat-control layer. According to Threlfall, the result is far more effective than a single covering alone, giving much greater control over the temperature and airflow in a room throughout the day.
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Debbie Leigh, design manager at interior textiles company ILIV, explains that the most effective stacks combine light-filtering and heat-blocking layers. She recommends starting with a sheer or voile fabric close to the glass to diffuse strong sunlight without completely blocking it. Next, a well-fitted blind, such as a blackout or thermal roller blind, should be added to be pulled down during the hottest parts of the day. For the final layer, curtains can be used, which can be adjusted depending on the time of day. These also add a layer of insulation when temperatures drop in the evening.
How to set up the airflow
The physical setup of the windows is just as important as the fabrics used. Anton Neike, cooling and energy expert and CEO at Taupia, notes that ideally you need two sets of openings, one lower down and one higher up. You should start by opening a window on your ground floor, ideally on the cooler, shaded side of your home. Then, open a window on an upper floor, such as a bedroom window or roof window, to let the hot air escape. For best results, open the bottom sash of your lower windows to let cool air in and the top sash of your upper windows to let warm air out. If you have a two-storey home, opening first-floor windows on the windward side and second-floor windows on the opposite side works brilliantly.
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A common mistake is opening windows during the hottest part of the day, which lets hot air in and actually makes the home warmer. Neike states that the stack effect only works when the air outside is cooler than the air inside, so it is best used in the early morning and late evening after sunset. Another mistake is relying on fabrics that are too heavy, which can trap heat rather than reflect or diffuse it. Over-layering can also reduce airflow around the window, making rooms feel stuffy if everything is kept closed all the time. On a similar note, you need to ensure the window dressings are layered in a flexible way as if they are too difficult to adjust it becomes harder to respond to changing temperatures throughout the day.
