Energy-saving windows: The clear choice

With temperatures down and the cost of electricity up, energy efficient house design continues to be a hot topic.  And although it’s finally also becoming a priority for local architects and housing developers,  an estimated  90% of South African homes remain inadequately insulated and vastly inefficient in terms of energy consumption.  Ceiling, pipe and geyser insulation is a good place to start if your aim is to start saving energy, at a relatively low cost. However, if you’re prepared to invest a bit more with the aim of a long-term energy saving investment, a step in the right direction would definitely be to replace your home’s existing 4mm float glass windows, with energy efficient windows made from low-e glass.

Windows are a critical element of any house design and fulfill multiple objectives: they allow in natural light, fresh air, provide outside views, and are fundamental to the aesthetic. Who doesn’t love big windows that allow morning light to stream in, or sweeping views of a lush garden? Unfortunately windows can also be weak spots in a home’s thermal envelope, and could be costing you money. Thankfully glass and window technology has improved significantly in recent years, and high-performance windows now make energy-efficient homes possible with much greater freedom of design than ever before.

Whether considering a new build or a large-scale renovation, including energy efficient windows should be a priority. When choosing windows, it’s critical to purchase the most energy-efficient windows you can afford, because they will pay for themselves over their lifetime. Energy efficient windows come in different forms, the most commonly known as double-glazed or low-e. Low-e coatings provide various performance levels and the glass can be used in a variety of ways including single glazing, laminated glass or double glazed windows. Double-glazed windows use twice the amount of glass as standard Low-e windows, and are therefore very costly.  For a  relatively mild winter climate like South Africa (compared to the colder northern countries such as USA, Canada and Europe), low-e glass is a very good alternative to double-glazed windows.

Low-e is standard clear glass  with a special thin metal coating on one surface. The E in low-e refers to low emissivity and describes the capacity of a surface to radiate heat. Emissivity is measured across a scale from 0 to 1, where 1 represents the highest emissivity. Low-e glass can reduce the amount of heat loss by around 30% compared to ordinary glass. It also improves thermal efficiency by cutting glare and preventing damage interior furnishing caused by ultra-violet rays.

New generation low-e often uses laminated and toned glass combinations to provide superior performance over non-coated glass. The most effective solution is found by combining a low-e coating with double-glazing, such as has been done in Stand 47 where outdoor temperatures can reach well below freezing during winter. By using low-e coating and a suitable frame that limits the transfer of cold air, it’s possible to stop up to 70% of heat loss and 77% of heat gain when compared to standard glass.

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