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The zero carbon agenda is driving changes to Part L, steering inexorably towards delivering zero carbon buildings by 2019. But while developers and landlords have been preparing for this new legislation for the last couple of years, its impact on tenants – and in particular on retail tenants – is only just starting to be noticed.
Of particular significance to retailers are new tests for solar gain through the shop front, and artificial lighting allowances. Changes to the regulations now mean it is very difficult to have a clear glass, highly transparent shop front, with low-efficiency spot lighting within the retail area.
A very large proportion of high street retail space relies on permeability of the shop entrance, and visibility into the store. Except for the dressed windows of large department stores, this transparency of frontage is vital for displaying the goods effectively within the shop and encouraging customers in to spend.
However, recent changes to Part L – and in particular the introduction of the solar gain test to reduce overheating through the façade - are making it increasingly difficult for shop fronts with extensive areas of clear glass to pass Building Regulations. The regulations require that any conditioned space behind a façade must comply with the solar gain test, even if it is a display frontage
Solar gain test
In order to pass this solar gain test, the area of glazing used in shop frontages needs to be reduced substantially. The only other alternatives are that a darker tinted glass is used or some form of solar shading is employed.
The problem is that either reducing the area of glass or making it darker are options that both tend to conflict with retail tenants’ briefs for the full-height, clear glass facades that best display their products. Darkening the glass can alter the appearance of clothes, particularly for fashion retailers, whilst reduced areas of glazing can give the appearance of reduced transparency.
Providing solar shading is not without its problems either, because devices such as brise soleil can also be difficult to incorporate once a scheme has planning consent.
To further complicate matters, there is no standard approach that will give a consistent output from the assessment method. This is because the solar gain – and therefore the measures required to control solar gain – varies from project to project, depending on the glass type and extent of glazing used, as well as the orientation and location of the building. For example, projects in the north of the country generally find compliance with the criteria marginally easier, due to the reduced solar intensity at higher latitudes.
So what does this mean for new retail space? It is becoming more apparent that early discussion between developer and tenant is key to establishing how best to ensure that the retail space is designed and built to comply with regulations, while also giving retailers the frontage they require to ensure the shop maximises its potential.
The use of brise soleil or other means of creating shade on the façade is probably the simplest way of passing the solar gain test and complying with the requirements of the regulations. It is likely that in the future, solar shading will be increasingly incorporated at the design stage to allow a wider choice of glass types for retail frontages. However, this option is limited to schemes that do not already have planning consent.
For projects that have gained planning, but have not pre-registered with building control for submission under the 2006 regulations, other solutions are required. So is there another option that can be explored before the glass type or extent has to change?
Traditionally the partitions between the building façade and the shop unit have been plasterboard stud walls, which again do not allow visibility through a display window in to a shop interior. However this does not suit the brand image or identity of many retailers, so an alternative solution is needed. One such option is the creation of an un-conditioned zone between the façade and the shop unit – effectively a glazed inner partition where a dressed window can be created. In future, retailers will need to look at these and other innovative solutions to ensure they meet ever more stringent Part L regulations.
Dave Wakelin is associate sustainability consultant at Hilson Moran .
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