Stricter standards implemented in the Part L regulation in England came into force on June 15th 2022 and will be a crucial interim step towards achieving the Future Homes Standard by 2025, as well as contributing to the ambition to deliver nearly zero energy buildings (nZEB) in the UK.

The implementation of the changes outlined in the supporting approved documents is expected to lead to up to a 31% reduction in carbon emissions in dwellings compared to the current standard. Achieving this will require embracing carbon-saving technologies, such as low-carbon heating systems, as well as improvements in building fabric standards.

A ‘fabric first approach’ is key to meeting the new building requirements

Key to meeting the new requirements is a fabric first approach, where a buildings’ materials are prioritized for maximizing energy efficiency. In the case of glass and glazing, this means limiting fabric parameters, or ‘back stop’ values for building elements such as windows or doors. These ‘back stop’ values, or U-values, refer to the rate of heat transfer through a material, divided by the difference in temperature across that material.

Lower (better) U-values will contribute towards the overall target performance of the building and help meet the new requirements. For windows in new dwellings, the previous maximum U-value of 2.0 W/(m2·K), has been tightened to 1.6 W/(m2·K). For replacement windows in existing dwellings, the maximum U value is now 1.4 W/(m2·K), down from 1.6 W/(m2·K).

However, the expectation is that the U-value will still have to be much lower than this to enable new dwellings to achieve the target primary energy, carbon emissions and fabric energy efficiency rates, with a window U value of 1.2 W/(m2·K) referenced in the notional dwelling specification. Thinking ahead to the Future Homes Standard, a reference window U-value of 0.8 W/m2·K is anticipated.

The role of triple glazing

Insulating Glass Units (IGUs) with higher thermal insulation specifications may be necessary for projects to help prevent heat loss through windows and meet the tighter regulations.

Although a somewhat divisive topic within the industry, it is worth noting the operational performance and carbon payback of triple glazed windows.

New research from Glass for Europe, based on public data and energy performance models, tells us that the carbon payback of low-E triple glazed windows over low-E double glazed windows can be as short as 35 months, dependent upon factors such as climate and heating system.

The study concludes that high-performance triple glazing offers benefits in terms of reduced operational CO2 emissions that largely outweigh the incremental embodied CO2 emissions compared to high-performance double-glazed windows.

Amplified by an increase in specifier queries on the U-value of our products, as well as the options when it comes to triple glazing, any new glass products will need to demonstrably limit heat loss, for old or new dwellings. Undoubtedly, triple glazing is part of the solution.

Glass solutions

Of course, it is not just triple glazing but a whole host of glass and glazing solutions that unlock huge potential for energy saving and CO2 emission avoidance. Insulating glass units can be installed into many types of existing window frames, and specialist coatings can modify products to make them more energy efficient during manufacture on-line or subsequently off-line.

Window Energy Ratings (WER) are often used as a means of demonstrating compliance with Part L for replacement windows in existing dwellings and take into account the total energy performance of a window.

The rating doesn’t only look at heat loss, but also at the amount of the sun’s energy passing through the glazing.  As an alternative to the U value compliance route, replacement windows achieving minimum WER band B can satisfy the new requirements.

Solar control glazing allows daylight to pass through a window or façade while reflecting away a large degree of the sun’s heat. For example, Pilkington Suncool™ is specifically designed to ensure buildings don’t overheat during the warmer months and also helps to reduce the need for both cooling and heating systems.

From an earlier Glass for Europe study, we know that by using high performance solar control glass adequately, annual energy savings of 28% from cooling can be achieved in 2050 in Europe.

Where there isn’t a need for cooling systems, incorporating a low-e glass such as a glass from the Pilkington K Glass™ Range or Pilkington Optitherm™ S1 Plus helps to prevent heat from escaping through windows, reflecting it back into the building, allowing architects to use more glass.

Changes to Part L are just the beginning

As we look to the future, it is important for installers to be prepared for the tightening of these regulations in the run up to the introduction of the Future Homes Standard in 2025.

The changes to Part L are just the beginning, so understanding the energy performance of your chosen glass and pre-empting further tightening of the regulation will play a significant role in meeting the targets in the coming years.