News: Energy Efficiency of Windows & Doors

Dale Windows helps transform 1900s house into contemporary 5 bedroom family home


Energy efficiency is an increasingly hot topic in the building trade. As people’s knowledge and understanding of the benefits available has increased, so too has demand for more energy efficient products.

Whilst to some energy efficiency may mean renewable technologies such as solar, biomass or A-rated appliances and LED lighting, it’s worth considering that around 35% of the heat generated in a property escapes through the walls and gaps in and around the windows.

So when it comes to a refurbishment, extension or retrofit project, getting the basics right can make a major difference. What the doors and windows are made of, the glazing options and the style, right through to how they are installed can all impact on the energy efficiency provided.

Here we take a look at some of the key things to consider.


When it comes to the energy efficiency the more you can slow the amount of heat travelling from the inside to the outside, the more energy efficient a property will be. And when it comes to windows and doors there is more to look at than simply opting for low U-values.

What Material?

 What material you go for will depend on a number of factors and you may be forgiven for thinking that modern materials such as PVC-U, offer better performance than traditional materials such as timber.

For replacement windows, the Centre for Alternative Technology recommends good quality timber frames, requiring little energy to manufacture, that can last over 50 years, and then be renovated rather than replaced. Timber also has a low thermal conductivity helping reduce cold-bridging.

In a report commissioned by Heriot Watt University in 2013, the results revealed timber frames to have an expected life service of between 56 and 65 years. PVC-U came in at 25-35 years.

Style options

There are a growing number of window styles on the market today, but some are better than others when it comes to energy performance. If keeping the warmth in and the weather out is important – particularly where properties are exposed to the elements on the coast or on moors then careful consideration should be given to the appropriate style/design. This will help protect against extreme weather conditions. The highly efficient double glazing units and draught stripping maintain excellent insulating properties.

Opt for windows manufactured using a robust multi-layer timber process that is warp and twist resistant, engineered to last.

Technical Accreditations

Look for windows that have been independently tested and approved in accordance with BS 6375-1:2009 and BS 6375-2:2009

Part 1 – Weathertightness

Part 2 – Operation & Strength

And exceeded requirements for:

Air Permeability (EN1026)

Watertightness (EN1027)

Mind the Gap

The panes of glass in double glazing are separated by a spacer bar. Traditionally these have been made from aluminium, which conducts heat out around the edge of the unit. Insulating spacer bars, sometimes referred to as ‘warm edge’ spacer bars have no metal content and are therefore considered much more energy efficient.


Around 66% of the energy lost from a standard window is through the radiation travelling through the glazing. This thermal transmittance of a glazing unit is known as the U-value.

When it comes to selecting windows, the lower the U-Value, the less heat loss and the more insulation provided

Consider as standard double glazed units featuring performance glass along with warm edge spacer bars and argon gas for superb insulation. Look for U Values of 1.1 W/m2K (centre pane u-value) which equates to 45% more energy saved than with ordinary double glazing, 80% more than single glazing.

Unless your client is specifically asking for the highest performance windows possible, the British climate means you won’t really need to go as low as -20 or as high as +40 degrees, so think before you pay for a performance feature you won’t really gain from.

Fully Factory Finished.

Every element of window and door manufacture done in isolation is going to have a potential impact on energy efficiency. Window frames that are manufactured then delivered to site and separately glazed, primed, painted/stained are open to inconsistency.

Consider windows and doors that are made-to-measure (to the specific sizes required for the property for a better fit) with options to select the specified glazing styles and finishes needed. These will arrive on site fully finished and ready to install complete with manufacturing guarantees across the timber, workmanship and paint or stain finishes.


The installation of an energy-efficient window is as important as its manufacture – a poorly installed window can be hugely inefficient, perhaps increasing heat loss by as much as 30 per cent.

Positioning of the window in relation to the insulation, and how far back within the wall it is set, are both important factors.

In Conclusion
There are a few key steps to take to ensure your customer can enjoy additional energy efficiency levels from their windows and doors.

For more information call us on 0800 030 2222 or email or visit our range of windows and doors at

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