Kris Bennell of Associated Steel Window Services discusses how the company helps heritage, W20 and other traditional steel and timber windows attain contemporary standards of energy performance.
Over the last few years, Associated Steel Window Services has seen an increased desire and necessity to bring older windows into our modern building requirements. As a leading specialist in the refurbishment of steel, timber, cast iron and aluminium windows, our clients’ and often our architects’ preference is for refurbishment. This obviously has its own significant benefits by reducing the impact of manufacturing and sourcing new windows, often lowering the impact on a projects BREEAM aims and aiding in the Net Zero Carbon Assessment. In a world where heritage is often seen as outdated or in need of replacement, ASWS is able to offer a modern upgrade on windows that brings the traditional window into the modern world of performance and energy efficiency.
Building owners, and specifiers, realise the aesthetic appeal of retaining traditional steel windows when restoring an older property; Universal Suite, W20 sections and other frame types suit every building from dockland warehouses to Art Deco villas. The slender sightlines and glazing patterns complement brickwork and render across multiple architectural styles, but the accepted wisdom that steel simply cannot satisfy the thermal performance requirements leads to many project teams seeking alternative solutions.
There is, though, genuine and growing cause for taking a more positive and proactive attitude to existing windows of any material, even if they are suffering from corrosion in the case of steel, or rot in the case of timber, misalignment, and poorly maintained or missing fittings.
Not only can they be fully refurbished and put in good working order, but their notorious draughtiness and the heat-sapping thermal transmittance issues can be improved to the point where a number of restoration projects have successfully targeted the higher levels of BREEAM – without replacing the old windows. There are even points available within BREEAM assessments for saving the original fenestration from the scrap yard.
ASWS is currently working with RED Construction on The Harrison, Curtain Road, a Grade II listed structure which offers circa 40,000 sq. ft. of space for rent across five floors; with an accreditation of a BREEAM Excellent achievement and a top EPC rating of ‘A’. Image credit CGI by Hut Architecture
The ideal starting point is to have an experienced window specialist, such as ASWS, carry out a full condition survey prior to any work beginning on site with the likelihood of the drawings, observations and detailed recommendations often being incorporated as part of the tender documents – or put forward to the conservation authorities as part of the planning or listed building application.
Inevitably, listed building status significantly limits the interventions which can be made but taking advantage of modern glazing technology is just as important as diligence in overhauling the frames themselves and understanding that leakage occurs around the frames and the fabric of the walls, as well as through the vents themselves.
While standard 4mm glass delivers a centre pane U-value of just 5.8 W/m2K, swapping this for a 12mm Eco Slim DGU can reduce this wasteful figure to 1.9 W/m2K. Better still, utilising option of vacuum glass units, the centre pane U-value falls to a far more efficient 0.4 W/m2K. Importantly, there are documented figures available on different glazing solutions which can deliver an automatic improvement to EPC scores while the use of infra-red thermal imaging can dramatically highlight the difference between the before and aftereffects of window upgrades.
It is also worth pointing out that, although vacuum units remain an expensive option, their construction avoids the issue of a double reflection being created across the window when viewed from outside, which often leads conservation officers to oppose their inclusion on buildings of historical importance.
Quantity surveyors may be regarded as the construction industry’s bean counters, but the entire project team is nowadays tasked with cutting its carbon footprint by reducing waste and sourcing products in a sustainable manner. So, when working out the overall impact of a large renovation scheme, having avoided replacing the old fenestration – with all the additional lorry journeys and impacts of landfill or recycling – can offer a significant win. Accordingly, every activity which is carried out by the window restoration specialist is logged in its BREEAM assessment. This will include not just the number of deliveries and origins of products used, but also items such as the FSC certification for timber. And finally, when a project is completed, there can be a certificate of improvement relating to energy loss through the façade, which confirms the gains to be achieved through comprehensive fenestration upgrades.
The other significant benefit of a steel or timber window refurbishment is getting windows to operate properly. Often, after years of poor maintenance or over painting, windows do not operate how they were intended to, and this means there is significant air leakage as well as poor closure. Both are significant issues on a building’s energy efficiency and have a significant impact on the building’s usability for the tenants or owners.
