Windows are an important part of sustainable buildings. With clever construction and technology, your indoor environment can be efficiently cooled, lit and heated.

Large windows are more likely to lose or gain heat than smaller ones, and south-facing windows allow more heat and light to enter than north-facing ones. Awnings and overhangs may let in winter sunlight and provide shade in hot months.

Energy Ratings

The British Fenestration Ratings Council (BFRC) has introduced a rating for energy performance, with categories running from A to G. Calculations are based around:

– U-Value – a reading of heat loss
– Solar Heat Gain Co-efficient (SHGC) – measures how much heat a window will absorb from sunlight.
– Air Leakage (L50) – measures how much air leaks in and out of a closed window.

Type of Frame

Frames can significantly affect the way a window works. Wood is sustainable, but it can be costly and needs painting frequently. Fibreglass is easy to maintain and energy-efficient but can be pricey. Aluminium conducts heat readily and is less energy-efficient.

PVC is a favourite. It is made from vinyl and is cheap to buy, energy-efficient and easy to maintain. Painting is not necessary, and it is water-resistant. Vinyl frames give improved thermal performance when they are insulated.

A Dublin windows and doors specialist such as can advise on options. For more on energy-efficiency, see

Glazing Options

An energy-saving window has two or more glass panes separated by an air gap to delay heat transfer and provide noise insulation. Modern versions use krypton or argon for improved thermal performance.

A metallic coating called low-e is new. Windows treated this way are intended to lower heat flow – by reflecting heat back into the building or back outside.

In between the glass layers in a window, spacers are used to steady them. Spacers used to be made of aluminium, but thermal insulation was poor and condensation problems developed. New warm edge spacers have a high thermal efficiency: materials include fibreglass, silicone foam, vinyl and reinforced thermoplastic.

Eco-Friendly Designs

In the last 20 years, windows technology has been revolutionised, with customers saving both money and energy. Crucially, energy-efficient windows lower carbon emissions and help to tackle global climate change. Combined with green building technology, they are your best choice to help the environment.

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