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2 April 2025
ASWS explains how dated windows can achieve modern standards of energy performance
Laura Mercer, Managing Director ofAssociated Steel Window Services(ASWS),reflects on the steps available to help heritage W20 and other traditional steel and timber windows attain contemporary standards of energy performance.
New horizon on energy performance for traditional steel windows
Together with building owners, most specifiers can see the aesthetic benefits of retaining traditional steel windows when restoring an older property, whether it is subject to conservation requirements or not: Universal Suite, W20 sections and other frame types generally suit everything from dockland warehouses to Art Deco villas. The slender sightlines and glazing patterns undoubtedly complement brickwork or 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 have poorly maintained or even 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 radically improved upon to the point where a number of restoration projects have successfully targeted the higher levels of BREEAM - without replacing the old windows. In fact, there are even points available within BREEAM assessments for saving the original fenestration from the scrap yard.
The ideal starting point is to have ASWS, an experienced window specialist, 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 even put forward to the conservation authorities as part of the planning or listed building application.
With commercial work accounting for a high proportion of its portfolio, ASWS has been involved on some of the most challenging redevelopments to have been carried out over recent years, including at Woolwich Arsenal, Hackney Town Hall, Battersea Power Station and former BBC premises, Bush House. 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.
Significantly, on one of the projects where ASWS is currentlyworking,The Harrison for RED Construction, none of the windows actually closed properly, representing a huge waste of heat and poor comfort levels. The desktop EPC assessment process does not take this situation, or its resolution, into proper account.
The easy wins in a lot of cases are to ‘reset' the opening lights - where the skilled engineers physically straighten the vents so that the edges meet correctly - before new draught-stripping is applied. Then, as almost all old steel windows will have been single glazed, there is the opportunity to upgrade this, depending on the depth of rebate.
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 to1.9 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.
Embodied energy
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.
ASWS offers a full range of survey, repair, replica replacement and maintenance services for all ages and types of metal and timber windows. For more information on ASWS, please visit asws.co.uk.
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Note to editor
ASWS is a long-established member of the Steel Window Association and well-recognised expert in the repair of metal windows, from the earliest wrought iron examples through to contemporary curtain walling. ASWS also undertakes full restoration works to all timber windows and doors, architectural metalwork, specialist glazing, bronze windows and shopfronts. As well as in-situ servicing and restoration, the company frequently removes frames back to its London workshops for repair, or to produce replica replacements. Further services include carrying out full condition surveys, retrofitting thermal glazing upgrades and enablement works for demolition and other contractors, where fenestration can be documented and removed to secure storage for the duration of a project.
With compliments:
Taylor Alden Ltd
media@tayloralden.co.uk