Housebuilder & Developer’s James Parker speaks to IDSystems’ David Clarke, to discover how the 2021 changes to Building Regulations have driven the specification of better glazing systems for new build and retrofit domestic projects.
How have the changes to Part L thermal requirements improved glazing specification?
The tightening of Part L since 2021 has made thermal performance a core driver of glazing specification rather than a secondary consideration. There is now a far greater focus on U-values, thermal bridging and whole-system performance, with glazing being recognised as a critical part of the building envelope. Improvements in glass technology mean that frames, rather than glass, are often the weakest point, which has driven better frame design and more considered system engineering. Overall, Part L has raised standards, retired older, poorer performing systems and pushed manufacturers to develop higher performance products without abandoning aesthetics.
How have you seen specifier awareness among developers change over the years around glazing systems, evidenced in the audience research we’ve undertaken?
Specifier awareness has increased significantly over the past three to four years. We were part of research with Housebuilder & Developer that showed relatively low awareness among housebuilders, including limited understanding of upcoming changes around Part L and Part O as well as the path to Future Homes Standard. Since then, knowledge levels have improved markedly. Developers, architects and housebuilders are now much more conscious of regulatory compliance, thermal performance and long-term implications of product choices. This awareness has filtered down from architects to developers and end clients, creating more educated and discerning customers who no longer simply replicate previous specifications for new projects.
Why have sliding doors overtaken bifold doors to become the go-to option for glazed doors on extensions, renovations & new-build projects?
Sliding doors have benefited from several converging factors. Thermally, they are capable of outperforming bifolds because they have more glass and less frame, and frames are now
the weakest thermal element. Aesthetically, they offer larger panes, slimmer sightlines and uninterrupted views, which suit contemporary design trends. Practically, sliding doors are easier to install and maintain, and in the British climate they remain closed for most of the year, making visual aesthetics more important than full opening width. For developers, they also offer a better balance of performance, cost, longevity and compliance.
What are the benefits of working with a supplier who provides the entire design & manufacturing service?
A fully integrated supplier offers greater control over quality, performance and regulatory compliance. By designing, manufacturing and installing in-house, companies like IDSystems are not constrained by third-party system limitations and can engineer solutions specifically to meet building regulations. This reduces risk, avoids passing responsibility between parties and ensures accountability throughout the project lifecycle. It also allows earlier and more meaningful collaboration with architects and developers, leading to better coordinated, more reliable outcomes.
What are the impacts you’re seeing on residential designs of having to manage the balance between Parts L & O of the Regs?
Designers increasingly have to find a compromise between maximising the amount of glazing against thermal efficiency (Part L) and overheating risk (Part O), particularly on south-facing elevations in London and the South East. This has led to more considered facade design, sometimes reducing glazing areas, and greater use of shading strategies such as overhangs, brise soleil and integrated design solutions. There is a growing recognition that the whole building envelope must work together, as excessive glazing can undermine energy efficiency if it leads to increased reliance or use of energy-hungry air-conditioning units.
What is the future for trickle vents? Do you still have to include them or has mechanical ventilation made them obsolete?
Trickle vents remain a regulatory requirement under Part F of Building Regs and therefore must still be included for most new-builds (and extensions and replacement work). However, they are sometimes seen as an undesirable and somewhat illogical solution, as they can compromise airtight, thermally efficient systems. Mechanical ventilation is becoming more common and may reduce reliance on trickle vents in the future, but for now they remain part of compliance. There is an expectation that future regulations may address this more holistically.
Are you seeing increased market share for aluminium versus PVC, driven by sustainability?
Yes, aluminium is increasingly favoured, particularly in higher-end residential and developer projects. It is associated with high performance, durability, slimmer frames and premium aesthetics, all of which align with current design and sustainability expectations. While not stated as a wholesale replacement for PVC across all sectors, aluminium’s performance credentials and longevity contribute to its growing appeal, as it has infinite recyclability.
Why are bonded systems to be treated with caution?
Ultra-slim bonded sliding door systems permanently fix glass to the frame, which creates long-term risks. If the glass breaks, replacement often requires the removal of the entire panel and reliance on the original manufacturer still producing that system. This can be costly and problematic years later, especially if the manufacturer or system is no longer available. Non-bonded, dry-glazed systems where the glass is secured in place by beads allows double or triple glazed units to be replaced independently, offering better long-term serviceability, reduced risk for developers and homeowners, and greater resilience over the lifespan of the building.
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