Green Services Direct

From energy efficient glazing to sustainable materials, discover how to make a more planet-friendly choice

Whether you want to protect the planet or just cut your fuel bills, making your home as energy efficient as possible through the installation of double or triple glazing is a no-brainer. Few people would consider installing single glazing today - and in fact, today’s Building Regulations don’t allow it apart from listed properties.

Climate change is a hot topic that has made us increasingly aware of the urgent need to reduce our impact on the environment. Shopping for windows is no exception. New builds and extensions often feature large swathes of glazing – bifold doors, picture windows, rooflights – but all glass has implications for energy efficiency because heat escapes through it more readily than through an insulated wall. By making a more informed and responsible choice, you can reduce your carbon footprint, save money on bills and create a better-insulated, comfortable home.

Energy efficiency & insulation

One of the most important glass performance measures is U-value. This shows how much heat flow, or heat loss, occurs through the glass due to the difference between indoor and outdoor temperatures.  Meanwhile R-value measures the insulating capacity. The lower the U-value, the better its insulation.

To comply with the latest Building Regulations, windows must achieve a U-value of no higher than 1.4 W/m2K or watts per square metre per degree kelvin. This can be eye-opening for those who still have single glazed windows, as they usually exceed 5.2W/m2k. Meanwhile the most energy-efficient double or triple glazed windows available today can go as low as 0.7 W/m2K.

The British Fenestration Rating Council provides a helpful colour-coded rating system. The best performing windows which keep the heat in are rated A++ going down to E (the worst). Legislation in the UK now requires all new and replacement windows to be a minimum ‘C ‘ rating to help reduce our carbon footprint.

Materials:  

Timber

Timber is a popular option when prioritizing energy efficiency as wood is naturally a great insulator. Timber is also relatively unprocessed with low levels of embodied energy and a smaller carbon footprint than uPVC or metal frames.  The BRE Green Guide recognises timber as a sustainable material, rating timber frames A or A+ for sustainability.

You can be assured your timber windows are from responsibly managed forests by checking if it is FSC (Forestry Stewardship Council) certified.

Modern microporous paints and stains have made timber windows easier to maintain. These products are absorbed into the wood, so they don’t flake or blister and should only need reapplying every 8-10 years.

Aluminium

Perhaps you like the look of aluminium but are worried by its significant carbon footprint? Aluminium is possibly more sustainable than you might realise. It’s known as the ‘green’ metal as it is 100% recyclable. Recycled aluminium uses just 5% of the energy it takes to create produce the metal from raw materials.

Aluminium is lightweight and very strong, making it a good choice where large expanses of glass are required. It is extremely durable and resistant to corrosion as a powder-coated finish needs little upkeep.

Metal frames used to be synonymous with poor energy efficiency. But thanks to modern thermal break technology (where a less conductive material, such as a plastic insert, separates the interior and exterior aluminium profiles to reduce temperature transfer), today’s aluminium windows are far more energy efficient than ever before.

Aluminium clad windows

Originally designed in Scandinavia, to cope with incredibly harsh winters, these windows combine a low maintenance, thermally broken aluminium frame with the eco credentials of a timber interior. Remember to check if the aluminium is recycled and the timber is sustainably sourced with FSC certification.

uPVC or Unplasticised Polyvinyl Chloride.

While uPVC windows are often the most affordable option, they are highly energy intensive. Plastic windows typically score badly for climate change, water extraction and fossil fuel depletion. On the upside, uPVC window frames have a surprisingly long lifespan and can be recycled. The plastics industry says uPVC profiles are a sustainable choice as they can be recycled up to ten times, providing about a total 350-year lifetime.

Check with window manufacturers what percentage of recycled content, if any, is in their frames.

Durability

Windows that last for decades can help reduce waste and the need to manufacture replacements from raw materials. As with other products, warranties can be an indicator of the reliability of the window and its manufacturer.

Timber windows typically have a longer lifespan than plastic windows. During the average 60-year life cycle of timber frames, UPVC frames would have to be replaced at least once, says the Wood Windows Alliance. This increases the carbon footprint of uPVC frames considerably.

Glass specification options

It is thought that between 10-50% of a home’s energy is lost through windows and doors and 90% of that energy loss is through the glass itself. Manufacturers are having to up their game and produce better performing products.

Low-emissivity or Low-E glass slows the rate at which heat escapes through the glass. Low-E glass is essentially standard glass with an invisible metal oxide coating on one of the inward-facing panels which  reflects heat back into the room.

Low-iron glass, also known as optically clear glass, is made from silica with reduced iron content compared to ordinary glazing. This type of glass can let in more of the sun’s energy and heat into your home, so is ideal for north facing properties.

Solar control glass absorbs or reflects solar radiation and is especially suited for south facing facades where there are large expanses of glazing to prevent overheating in summer.

Insulated with argon gas between the glass panels. This also improves energy efficiency as argon gas has a higher density than plain air, which helps to keep internal air from escaping.

Double or triple glazing.  As the name suggests double glazing includes two panes of glass while triple glazing has three. Both are excellent ways to insulate your home but triple usually comes out top in terms of energy efficiency and will help keep rising energy bills down. Triple glazing is an essential component in modern, ultra-low energy new builds together with very high levels of insulation and airtightness.

On the downside, triple glazing is significantly more expensive than double glazing and a lot heavier due to the additional layer. Glass is among the most energy intensive manufacturing methods, so it’s also about weighing up whether that extra pane is worth it for the bigger carbon footprint it will bring.

When establishing the eco-credentials of a window, look at the overall rating (A++ to E) and the U-value. Think also about the materials in the frame. Only choose a supplier that uses FSC certified timber or recycled materials – these are basic indicators that the product is likely to be a sustainable choice for your project. The glass specification also has a big impact on performance.

It’s always worth getting quotes from several companies and comparing the cost of each option.  It may be helpful to consult with a professional or conduct research online to find the best options for your home.