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Retrofit, restoration and the race to net zero
As the UK moves towards its ambitious goal of reaching net-zero by 2050, upgrading heritage and listed buildings to modern day efficiency standards is proving to be a stumbling block. Not only do these buildings hold key architectural and historic significance for the UK property sector, but the strict planning regulations restrict most changes that could improve the energy efficiencies of the properties. And given the UK has the oldest housing stock in Europe(1), halting improvements is a big portion of properties. In England alone there are 379,458 listed buildings and an estimated 2.8 million homes in conservation areas(2).
Sash windows first came to England in the late 17th century, and are a hallmark of Georgian, Victorian and Edwardian architecture. The design is linked to the aesthetic and historic values of these properties with the window style being just as popular now as when it was first introduced. Many of these windows were constructed with high-quality timber and single glazing that has stood the test of time but offers poor thermal performance by today’s standards. This creates a dilemma for homeowners and restorers, should they replace the sash windows with a modern alternative (if this is not restricted by planning regulations in the specific area), in doing so they will improve energy efficiency but alter the character of the building. Should they leave the windows as they are, the efficiencies will continue to decrease over time, resulting in increasing heating costs.
Although the regulations on listed and heritage buildings largely vary from region to region, all planning officers place stringent controls on the properties to preserve the architectural integrity. Owners must obtain consent before undertaking any changes that may impact the character of the building, with windows being considered ‘contributing elements’ of its heritage status. This means that restoration or repair is typically the primary option for window improvement, however this does not help improve the energy efficiency of the properties. Residential properties account for approximately 40% of UK carbon emissions, with that increasing to 42% by 2030, and older heritage properties are the worst offenders for energy inefficiency. Without updating policies and developing innovative approaches to retrofitting, these homes will become an obstacle to the net-zero target. Cushman and Wakefield also reported that 54% of homes in England have an EPC rating of D or lower, but around 12 million of these could be upgraded to a C rating or higher(3).
There are several different options when looking at sash window restoration within planning restrictions, that can help improve the efficiency of the property without impacting the overall look and feel of the sash window itself.
Vacuum glazing for heritage windows
Sash windows were typically made with a single pane of glass, meaning they are incredibly poor insulators, leading to significant heat loss. Vacuum glazing stands out as a revolutionary advancement in window design. The technology means that the two panes of glass that are typically slightly separated in double glazing, are enclosed together with a micro-thin gap thanks to the airtight space. Because of this, it closely resembles a traditional single-pane window. By retrofitting the windowpanes with vacuum glazing, it preserves the architectural integrity of the home, whilst enhancing energy efficiency. By preserving the historical features and being sympathetic to British historical architecture, it also complies with conservation regulations that most heritage properties are subject to. On average vacuum glazing offers a significant improvement in window energy ratings and a U value of 0.47 (compared to 5.82 in single glazed windows). Overall, vacuum glazing offers heritage property owners a sustainable and energy-efficient solution for improving the performance of the windows.
Secondary glazing for sash windows
An alternative option for heritage windows is secondary glazing. Not only does this retrofit style offer improved thermal efficiency and noise reduction, but it is also reversable and therefore an ideal choice for properties where permanent changes are restricted. Secondary glazing involves the installation of a fully independent internal window fitted on the internal side of an existing window.
Draught-proofing technology
Adding a draught-proof seal to sash windows is a fantastic way to improve the heat retaining features and overall efficiency of the windows themselves. Typical sealing systems such as brush seals can be beneficial, but full systems like the Ventrolla Perimeter Sealing System (VPSS) can offer a more tailored approach.
For the UK to achieve the ambitious net-zero targets, the regulations held over heritage and listed properties must be reviewed. The current rules place preservation over performance and halt any progress that can be made to improve efficiency. A balanced and slightly more flexible approach is needed, where the importance of conserving history is recognised, but sensible retrofits and restoration is allowed. Planning authorities must become more aligned with the rules and restrictions that are in place and create clear guidelines for all heritage property owners to help streamline any retrofits or renovations and reduce unnecessary confusion. Sash window retrofit is a fantastic way to drive meaningful progress towards the complex sustainability challenges, and it is one that should be placed at the forefront of the industries mind.
Due to the unique hidden and discreet design of Ventrolla’s VPSS, planning permission is not required when adding it to existing windows on listed buildings.
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