Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

Glazing over?

Glass cladding - Is the trend for glass-clad landmark buildings set to come to an end? Margo Cole reports on the latest thinking in façade design.

Part L of the Building Regulations has created a challenge for building designers in that they must now look at a building's performance in a more holistic way.

Levels of energy efficiency required in the Regulations - coupled with the possible implications of forthcoming energy labelling - are changing the mindsets of designers as they try to maximise performance.

One area coming under particular scrutiny is façade design, where the trend in recent years, particularly in high prole commercial buildings, has been for lightweight structures clad almost entirely in glass.

'Letting agents find it easier to market a transparent building, ' explains building physicist Mikkel Kragh, an associate at Arup.

'What they're selling is an image of a transparent building, but that's not what it's actually going to look like on the outside most of the time.'

The reality is that most fully glazed buildings need some form of shading - either planned or makeshift - to stop occupants overheating during the summer.

We may complain about the poor summers in the UK, but overheating is a very real problem in modern ofce buildings. Air conditioning can provide some relief, but - thanks to the introduction of Part L and its emphasis on reduced energy consumption - designers have been encouraged to look at alternatives, like natural ventilation.

'If you're looking at a lightweight building with lots of glass, you're not going to be able to cool it just by natural ventilation, ' says Faber Maunsell director Ant Wilson. 'The building will get too hot.' If that is the case, then the changes will have to come in the design of the façade itself, which could, ultimately, lead to a move away from entirely glazed buildings.

'There is always a balance between getting the daylight right and stopping too much solar gain, ' explains Wilson. 'Solar shading is effective at stopping solar gain, but you are also cutting some of the daylight out.' Kragh understands this dilemma, but approaches the problem from the point of view of the overall comfort of the people inside the building.

'Comfort is a complex issue and it is hard to quantify in a contract, ' he explains. 'That's why people try to simplify it.' He cites evidence that suggests building occupants can tolerate higher temperatures than those usually suggested if they have some level of control over their environment.

Building physicists like Kragh are often called in towards the end of the design stage to analyse the predicted performance of building elements or parts of the design.

But he believes they should be involved right from the start, and their expertise used to inform and optimise design at the outset.

'By appropriate analysis you can optimise performance and minimise or control risk, ' he says.

'People often forget the latter - they think it's a 'nice to have', but in actual fact we can prevent all sorts of risk.' This is particularly evident in façade design, where Kragh's approach is to consider the cladding performance at four levels: detail, system, room and building - returning to each level iteratively as the design progresses.

He has a range of analysis tools at his disposal. These can, for example, calculate the effect of the sun's movement on different walls, for how many hours blinds would need to be provided, and which areas of the building need articial heating while others need cooling down.

They can also study individual cladding systems to identify how they will perform. Used at the appropriate time, he says, these tools can be used to help designers and their clients look at all their options.

'You have an architectural vision and an energy benchmark, ' he says, 'and we can demonstrate ways of meeting those.' Early prediction of environmental conditions inside a building gives clients the opportunity to decide how to use the building, or to change their mind over the overall look of it.

For example, once they are aware which areas are likely to be subject to high solar gain they can decide to use these for circulation rather than as offices, or look at different levels of solar shading in different areas.

Alternatively, they might think twice about having a transparent building, and we may see a trend towards more limited areas of glazing or greater use of traditional materials in façade design.

Advances are also being made in glazing that may help with the solar gain/daylight balance, with coatings being developed that can let in more of the visual light spectrum while keeping out some of the heat.

Arup is also exploring new materials - such as composites - for cladding and curtain walling.

'We are starting to look at new materials in façades because aluminium is the worst material you could use as it is highly conductive.' The metal is traditionally used for cladding systems, but its ease of use and light weight must, according to Kragh, be weighed against the problem caused by cold bridging.

He is also concerned about the current fashion for curtain walling in high rise residential developments.

'In non-dwellings, you have high internal thermal gains, because they have a lot of equipment inside them, so the issue is very much about cooling the building, ' he says.

'But in dwellings the main issue is about heating them.

We are seeing a lot of high rise now coming through in the residential sector, which means we're seeing a lot of curtain walling. But the thermal performance of the systems may not be appropriate to residential buildings.' According to Kragh, Part L of the Building Regulations relating to domestic dwellings does not cover curtain walling - just walls and windows. 'Curtain walling performance is very much about the detailing of the frame, ' he says. 'If you don't carefully consider the framing, the input into your energy model is just going to be plain wrong.

I suspect that in a number of models the frame hasn't been considered - so the performance won't be as assumed.

'There's no such thing as a frame u-value on its own, ' he continues.

'It depends on the way it's built. So talking about a window u-value and a wall u-value is meaningless.' On the whole, Wilson and Kragh applaud the aims of the new Part L, although Kragh says what he does is 'nothing to do with Part L compliance - it's optimisation of the building'.

'What we are moving to is a performance-based method of designing, whereas before it was an elemental approach, ' says Wilson.

'Part L is encouraging holistic design, and if the result is that we get buildings that respond better, then that's good.'

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.