How the right glazing can boost energy performance in heritage buildings

Phil Brown, technical advisory service manager at Pilkington United Kingdom Limited, a member of the NSG Group, explains how the right choice of glazing can help improve energy efficiency in historic buildings without spoiling their aesthetics.

In Britain, we prize characterful old properties.

Houses with lots of original features in place command a premium in the market, and many public and private institutions take great pride in their grand historic premises.

But, while they are appealing in many ways, one disadvantage of heritage properties is their tendency to have very poor energy performance, and large, single-glazed windows are a significant contributor to this.

Normally, there is a simple solution – install double glazing. Unfortunately, putting in traditional double-glazed units (DGUs) can have a significant impact on a building’s appearance, making it undesirable. In the case of listed buildings or those in conservation areas, the stricter planning rules that often govern historic properties can mean it’s not an option at all.

Upgrade options

In conservation areas, the external appearance of buildings is protected, while listed-building status normally means it must be unchanged inside and out.

Traditional double-glazed units (DGUs) often cause difficulties because the extra thickness may not be easily accommodated in frames traditionally used with single glazing and the sightlines may be visible over the beads.

However, it is not impossible to upgrade to double glazing.

In some cases, choosing framing of the right material and colour for the building can reduce the visual impact of installing traditional DGUs.

If a property is subject to stricter planning rules, it is worth checking with the planning officer – especially in the case of a conservation area – as they may be happy to agree a design if it is sensitively done.

If this is not possible, another option is a product such as Pilkington Spacia™, a vacuum insulating glass that uses a vacuum rather than an air- or gas-filled cavity to deliver the same benefits as a high-performance DGU in the same thickness as single glazing.  In addition, as sound transmission through a vacuum is lower, superior acoustic performance can be achieved.

This will allow you to create windows that are visually almost identical to single-pane designs while enjoying all of the energy and acoustic benefits of double glazing.

A case in point

St Gerard’s school, a Catholic co-educational school in Bray, County Wicklow, near Dublin wanted to improve the energy performance in the oldest building on its site, Thornhill House.

The building dates back more than 150 years to before the school was founded and features large, sliding sash windows across two floors on all sides.

For this reason, the building was expensive to heat and difficult to keep warm during colder months of the year.

The school explored a range of options for window replacements and discovered that replacing all of the windows, as would be required to install traditional DGUs, would either entail a very high cost to be done sensitively, or have a big negative impact on appearance.

Instead, the school decided to replace the existing glazing with Pilkington Spacia™, keeping the existing frames.

As a result, heat-loss through the windows was reduced by almost 25 per cent, drastically cutting the need for heating, with no significant change to the appearance of the building, and no need to replace the frames.

The school also received positive feedback from teachers around the reduction in external noise levels in the classrooms, and how this had helped create a much-improved learning environment.

Improving the energy-efficiency of conservation buildings is likely to be a hot topic for Renovate Europe Day this month, on the 9th of October. The glass and glazing sector has a huge part to play in building stock decarbonisation targets, so let’s all use this day to spread awareness of how we can help and provide solutions.  

Check our YouTube channel ‘PilkingtonTV’, to see our latest video on Pilkington Spacia™ made in conjunction with Gowercroft Joinery, which shows how energy-efficiency has been boosted at the historic Repton School in Derbyshire.