Vacuum insulation glazing in refurbishing listed buildings

Monument conservation and energy efficiency often seem to be a contradiction in terms. However, innovative technologies such as vacuum insulation glazing (VIG) show how to reconcile both with each other. This method enables energy-efficient refurbishment without fundamentally changing the outer appearance of buildings.

Listed buildings are often distinguished by their unique character and their special architectural charms. This determines the cityscape and makes an important contribution to conserving our cultural and architectural heritage. Due to their age, however, many listed buildings are typified by low energy efficiency. This is often owed to the frequently used single glazing, which not only insulates poorly but also favours draught and condensation.

Anyone wishing to refurbish and upgrade a listed building energetically is, as a rule, faced with high requirements. Because monument conservationists want to ensure the authenticity and the preservation of the historical building’s substance in as unchanged a state as possible. To master this high-wire act the insulation of windows and doors is an efficient method – with so-called vacuum insulation glazing (VIG) being particularly suitable.

As a rule, insulation glazing units consist of two glass sheets connected with each other and with a sealed space in-between.

Until the 1980s this cavity was filled with air. For the requirements made on thermal insulation back then this insulation was sufficient and the window structure remained comparatively narrow and easy to produce.

But as the requirements made on thermal protection rose better u-values were called for. The u-value states the heat transition coefficient – the measure for how much heat (measured in Kelvin degrees of temperature difference) flows through a construction component per square metre (W/(m²K).

To reduce the heat loss, the cavity between the glass sheets was filled with noble gas such as Argon rather than air. These gasses have a lower thermal conductivity than air, thereby reducing the heat transition and improving the insulation.

However, the double or even triple glazing units usually used in new buildings cause problems with many historical window frames because of their size and weight. They cannot be installed without further adjustments made to the existing substance which results in conflicts with monument preservation. The solution: the markedly thinner vacuum insulation glass.

Vacuum insulation glass has a different operating principle than classic insulation glass. It does also consist of two glass sheets and one cavity but instead of filling this airspace with air, the air is largely removed so that a vacuum forms. Small spacers inside prevent the sheets from being pressed onto each other. 

Thanks to the technical composition of VIG, very low u-values can be achieved ranging from approx. 0.34 to 0.5 W/(m2K) depending on the system.

Next to its energy efficiency, the longer lifecycle of vacuum insulation glass is also of great importance because its saves resources. Another asset is the recyclability of these window systems that can usually be recycled clean-grade.

This is why vacuum insulation glass holds a high potential for the energetic and resource-saving refurbishment of listed buildings.