This article looks at enhancing window performance in each type of build that can be undertaken, as there is a lot to take into consideration for this one element of the building envelope.
Secondary glazing is an internal window, fitted into or onto the window reveal. It significantly enhances primary windows thermally, preventing heat loss and draughts; provides unparalleled acoustic insulation – cutting out noise nuisance and adds another layer of security. It is generally suited to listed buildings; however, it can be an equally important option for some new builds.
With land, on our small isle, at a premium, more and more of the plots being released for development are on brownfield sites which can come with their drawbacks. The main nuisance being noise, as often the areas are next to motorways, multiline rail tracks or airports. However, the dream can be attained, and the issue overcome.
When designing a new home, thought will need to be given as to how planning requirements will be met; so publications – such as BS 8233:1999 ‘sound insulation and noise reduction for buildings’, Planning and Policy Guidance 24: planning and noise, and the World Health Organisation guidelines – should be checked to ensure no issues are encountered down the line with planning departments.
If land purchased falls in one of the heavy noise areas, then undoubtedly high-performance primary double glazing would be the obvious solution, or even triple glazing. Yet, these systems can come at a high price tag and; in fact, not as effective as using a more rudimentary primary system in combination with an air gap and secondary glazing.
High-traffic areas can create noise in the region of 70-80 dB+; well-sealed standard double glazing (4-16-6) can reduce this by 34 dB. To put this into perspective, the WHO recommends bedrooms and living rooms have an ambient noise level of between 30-40 dB – so you can see, the system will not achieve this and disturbed nights’ sleep may ensue. By installing a more basic primary glazed solution and secondary glazing with a glass-to-glass gap of 150mm, a reduction of up to 48 dB can be achieved and even more if specialist acoustic glass is used.
These projects will often feature in a building which is; listed, in a conservation area, or is a change of use – i.e. church to residential. Again, especially in the case of listed properties or those in conservation areas, there will be many planning stipulations in place to stop changes being made to the historical details/architecture of the building or the surrounding area.
One of the weakest areas of the building both from a sustainability point of view and acoustically, are the windows. Generally, as part of the constraints, the original windows will need to be retained – which are often single glazed, draughty, allow heat loss and due to air gaps in the ill-fitting old frames – will allow noise to seep into the building. One of the only solutions to combat these issues is to install secondary glazing on the inside of the original window. It is a recognised solution and accepted by most conservation officers, as it is a reversible adaptation. This means that the secondary windows can be removed at any point in the future with little ‘making-good’ as it is a minimal intervention and a discreet treatment.
With the vast array of systems and styles in the market, it is possible to mimic the original windows and even have the secondary double glazing colour matched, to ensure it blends in with the surrounding decor, making them unobtrusive and unnoticeable. It will help reduce heat loss up to 60%, which; in turn, will have a positive impact on energy bills and reduce wastage – good for those whose priority is sustainable living. It can also help achieve Passivhaus and EnerPHit standards if a high level of sustainability is desired. It will have the same benefit acoustically as described above, creating a peaceful and relaxing environment. Additionally, even with a rudimentary system, it will add another layer of security, as single glazed windows are deemed more vulnerable and a soft target for burglars. Some systems on the market can also provide higher levels of security, including Secured by Design – the police preferred accreditation system – so always ask the supplier for evidence of testing and conformance if these products are required.
A recent conversion project, which had secondary glazing installed to meet planning requirements, was the change of use of a Grade II Listed 17th-century disused pub into a family home. Located on a busy thoroughfare in St Albans and having the original crown glass, and wooden framed windows; a solution was required to make it more thermally efficient as well as to reduce the noise ingress from passing traffic. Designs were drawn up and listed building consent sought (this should always be attained, even though secondary glazing is a retrofit solution). The plans were passed, and 16 units installed throughout the property. The owners are extremely pleased with the outcome, with a considerable reduction in their energy bills and barely notice the passing traffic outside.
What could be seen as a product of the past, is providing many benefits for a variety of building products. Systems and designs of secondary glazing have come a long way over the years and with the ability to shape and curve the aluminium frames, as well as colour them in a durable powder paint coated finish; you will feel the benefits almost immediately without noticing how they have been achieved.