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The Impact of Part L Building Regulations

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The Impact of Part L Building Regulations

Navigate the impact of Part L changes on usable space and development density. Explore the challenges of thicker windows and innovative solutions for a sustainable future in construction.

Thicker Windows, Thinner Walls: Navigating the Impacts of Part L Changes on Usable Space and Development Density

Recent revisions to Part L of the Building Regulations, which aim to enhance energy efficiency in new buildings, have introduced stricter requirements for window performance. Future changes to Part L are expected to further reduce the expected U-values. While this shift is undoubtedly positive for the environment, it also necessitates the adoption of thicker glass systems (currently triple glazing) and thicker window sections, which in turn raises concerns about the implications for wall thickness, usable house footprint, and the number of plots on a development.

The Thickening Window Dilemma

The new Part L regulations mandate that windows achieve lower U-values, a measure of their thermal insulation. To achieve these improved U-values, window manufacturers are increasingly turning to thicker glazing units and the next change is likely to mean widespread adoption of triple glazing. While these advancements undoubtedly enhance a building’s energy efficiency, they also come with a physical consequence: thicker glass requires deeper window frames. This is particularly true when you consider products like the sliding sash, where two panes slide behind one another and an additional 20mm of thickness in each glass pane could become an additional 40mm of overall glass thickness. 

Further to the thickening of the profiles to allow for the glass unit, manufacturers are also having to consider the additional weight of the glass units. Often this means heavier and bigger ironmongery, as well as further increases in the thickness and width of window profiles to handle the additional weight.

Impact on Wall Thickness and Usable Space

The adoption of thicker window frames invariably leads to an increase in wall thickness. While this may seem like a minor inconvenience, it can have a significant impact on the usable space within a building. In smaller dwellings, even a slight reduction in interior dimensions can make a noticeable difference in the overall living experience.

This reduction in usable space can also affect the layout and design of homes, potentially limiting options for furniture placement and circulation. Architects and developers may need to carefully consider these space constraints when designing new projects.

Implications for Development Density

The combined impact of thicker windows and increased wall thickness can also have ramifications for the density of housing developments. As the footprint of individual dwellings expands, the number of plots that can be accommodated on a given site may decrease. This could potentially limit the number of homes that can be built, particularly in areas with high demand for housing.

Adapting to the New Reality

While the shift to thicker windows presents challenges, it also presents opportunities for innovation and adaptation. Architects and developers can explore alternative design strategies to minimise the impact on usable space and optimise development density. For instance, they could consider using thinner internal walls or incorporating more open-plan layouts to maximise interior space.

Additionally, the industry can continue to push the boundaries of window technology, seeking ways to achieve superior energy performance without compromising frame thickness. This could involve developing new materials or refining manufacturing processes to create thinner, more efficient glazing units.

An Alternate and Less Disruptive Option

A good example of this is to use LandVac Optimum glass units. LandVac Optimum delivers thermal performance far exceeding triple glazing, while also having the flexibility to be as thin as a regular double-glazing unit. The price point for this unit is higher, but when compared to the cost of losing usable floor space or having fewer plots on a development, the cost of the glass is a minor factor.


The changes to Part L represent a significant step towards a more sustainable future for the construction industry. However, it is crucial to acknowledge and address the potential drawbacks of thicker windows, particularly their impact on usable space and development density. 

By adopting creative design approaches and encouraging further innovation in window technology, the industry can successfully navigate these challenges and continue to deliver high-quality, energy-efficient homes. LandVac Optimum offers an early solution to this problem which is oven-ready and can be incorporated into existing manufacturer profiles to ensure compliance today.

Find out more about Part L building regulations here.