Stuart Judge of the Steel Window Association considers the performance benefits of contemporary steel frames in terms of meeting the future challenges for housebuilding.
Britain can take pride in the way its big pharmaceutical companies and top research universities responded to the pandemic over the past year. We have proved we are world leaders in the fields of vaccine development and gene sequencing, and the UK’s construction industry was also among the fastest to adapt to new working practices in order to safeguard its workforce and customers.
Despite the media’s attention mainly concentrating on the Government’s handling of the pandemic, Ministers were meanwhile continuing to address other urgent issues including climate change and the necessary energy reduction measures. Accordingly, building product manufacturers and many specialist contractors were also readying themselves for further tightening of regulations intended to cut carbon emissions.
While the much-heralded Future Homes Standard 2025 has resurrected targets for ‘near to zero energy’ buildings (nZEB) and focuses on an ambitious switch away from gas boilers to heat pump and hydrogenbased heating systems, contractors and consultants will be compelled to target improved U-values and airtightness far sooner. SAP assessors will be seeking gains right across the building envelope, while still ensuring healthy ventilation; by either mechanical or natural means.
April 2021 saw the conclusion of the Government’s consultation on revising Part L of the Building Regulations (conservation of heat and power), and Part F (ventilation), along with the formulation of the Future Homes Standard. Further important changes, including ones scheduled to be implemented this December, will see significant emphasis on the role of fenestration in both new build and refurbishment projects across all types of property.
Surprisingly, however, many specifiers remain unaware that steel windows have continued to keep pace with the Building Regulations’ requirements for new-build as well as retrofit projects.
Thanks to the investment of time, resources and experience – much of it led by the Steel Window Association (SWA) – important technical product improvements, as well as greater choice in terms of style and opening options, have been regularly brought forward.
Most recently, the development of a new option for thermally broken steel frames means manufacturers here have access to an innovative suite of profiles able to meet the benchmark U-value of 1.4 W/m2/K, which will begin being used from June 2022.
Thermal breaks were introduced by the suppliers of aluminium systems as the replacement double glazing market began to mature in the latter decades of the 20th century, primarily to tackle the problem of condensation forming on the inner faces to the frame. They have changed in shape and sophistication since then, with many manufacturers preferring polyamide as the material to separate the aluminium extrusions.
The latest advancement for thermally broken steel profiles, though, uses polyurethane, which can offer multiple benefits beyond the strength to match the 60+ year life expectancy of contemporary steel window frames. Using polyurethane is more economical than the available alternatives without compromising on quality, and still delivers very low thermal conductivity.
Unlike previous options for thermally broken steel frames, which tended to be more bulky, the latest development retains the stepped-leg design of the W20 window, which suits such architectural styles as Art Deco and many of our 20th century warehouse and industrial buildings.
SIGHTLINES & SECURITY
Importantly, the modern ‘marque’ maintains the characteristic slim sightlines, together with excellent light transmittance and an aesthetic of openness. The inherent strength further facilitates large overall window sizes, not possible with framing types such as PVCu, unless they are reinforced using steel. The availability of tubular steel profiles further enables even larger spans and the fabrication of heavy-duty doors for high traffic locations.
Steel windows and doorsets are also able to meet the toughest requirements on security and resistance to burglars, and are frequently the default option where fire performance is considered of prime importance. In such cases, the glazing selection is likely to swap from toughened to laminated featuring special interlayers; or even the multi-layered products of the type which support pedestrians in such locations as the walkways at Tower Bridge, or Portsmouth’s Spinnaker Tower.
TARGETING ‘FUTURE HOMES’ PERFORMANCE
Returning to the residential sector, Passivhaus and other approaches to ultra-low energy building have seen a greater focus in the past 20 years, and have generally utilised the best-performing triple glazed windows available. At the same time, across the wider housing stock far more carbon emissions have been saved thanks to the widespread installation of double-glazing that makes use of low-E glass, warm edge spacer bars, and argon filling.
However, with the Future Homes Standard aiming for U-values below 1 W/m2/K from 2025, triple glazing is inevitably going to become the default, with new materials already in the pipeline to permit further performance improvements. Not only do Krypton and Xenon gas deliver better U-values than argon, but new types of glass featuring special treatments have been trialled which are able to achieve centre pane values below 0.7 W/m2/K.
The challenge for window manufacturers will be to achieve the desired overall fenestration performance by balancing the glass area with that of the frame elements.
The SWA’s technical advisory service has long been a trusted resource for both prospective customers and member manufacturers, and the association’s website is in the process of being redesigned to enhance its value and accessibility to all users.
Given the swathe of improved products and services – those already available and in the pipeline – the steel options available make them fully relevant to the needs of property developers and discerning homeowners. And, the development of ‘new generation’ thermally broken frames also ensures they will continue to satisfy Government ambitions for ‘Future Homes,’ combined with a secure UK supply chain.
Stuart Judge is president of the Steel Window Association