Lifting the curtain on façade thermal engineering

March 23rd, 2017 Posted in: Business Development

As buildings are increasingly judged on their performance as well as their appearance, the role of the thermal engineer is taking centre stage. We take a closer look at how McMullen Facades’ dedicated thermal engineering department is helping to deliver sustainable solutions that meet the required building regulations and exceed client expectations.

The rise of thermal engineering

With the need to reduce the environmental impact of a building being a prime design consideration, identifying ways to minimise heat gains and losses through the building envelope and achieve the desired U-values is paramount. The numerous revisions to Part L of the Building Regulations have led to heat loss targets being some 30-40% lower than they were ten years ago and this, in conjunction with more stringent air leakage values, has led to significant advances in building materials in terms of thermal performance. The need to understand, design and install facades that meet these ever-changing requirements has also led to thermal engineers becoming an increasingly important and valued part of the design team.

2D - Extract from of Thermal Report of Residential Project


3D - Extract from of Thermal Report of Residential Project


With this in mind, McMullen Facades created its first dedicated thermal engineer role back in 2008 and since then, through investment in the latest 2D and 3D thermal modelling software, ongoing staff training and increasing demand from our client base, the department has expanded both its size and level of expertise.

Facing the challenges

Glass and aluminium feature heavily in modern façades, with curtain walling systems, doors and windows having a huge impact on the overall thermal performance of a building. One of the most important aspects of a thermal engineer’s role is to look at how these different systems work together to achieve the lowest possible U-values whilst ensuring that any thermal improvements are practical and in no way detrimental to the overall structural or weather performance of the façade.

Keeping up to speed with the latest innovations is also essential as many aluminium fenestration products, particularly double and triple glazed units, have seen many improvements over the years in the quest to combat heat loss through the facades. The fact that glazing units constructed with warm edge spacer bars and Argon gas filled cavities are becoming the norm rather than the exception, and the surge in popularity of low emission and solar control coated glass, highlights the progress that has been made in this area.

In the frame

However the performance of the glazing system is to some extent, only as good as the aluminium frame retaining it. For our part, the McMullen team is continuously looking at ways to improve the thermal performance of our aluminium curtain walling, window and doors systems without any detriment to any other system performance requirements. This drive to reduce system framing U-values is a truly collaborative effort, utilising the skills and expertise from our research and development, structural and thermal engineering departments. By carrying out in-house thermal modelling, improvements can be identified and made to the system’s thermal breaks and gaskets and heat loss minimised by reducing the size of the air cavities within the thermal break zone.

It is vitally important that the correct balance is found between the façade infill panels and the framing system, as it is counter-productive to use high performance glazing units within a framing system with very poor thermal performance and vice-versa. This is one of the areas where the McMullen team of thermal engineers can advise on the most economical solutions, especially if it involves the design of bespoke framing systems.

Early engagement, lasting benefits

Ever decreasing building U-values can lead to overheating problems and as it is more expensive to cool a building using air conditioning than to heat a building, it is important that the right balance is found between thermal performance, solar gain and light transmittance. Again this is where McMullen’s in-house thermal engineering department can offer their clients help and advice. Sector experience is also important as there is often a considerable difference in the thermal performance requirements of a residential building and a commercial building and it is therefore important that system variations can be offered to meet the requirements of either building type.

Early Engagement Calculations to Assist Building Thermal Modelling.


Another unfortunate and sometimes overlooked side effect of lower U-values and reduced air leakage values is that these can increase the risk of condensation within the building or within the building fabric. Sometimes surprisingly, improving the thermal performance of a building element can be detrimental to the façade condensation resistance. The use of thermal modelling can prove essential in flagging up potential risks and more importantly, identifying cost-effective and practical solutions.

Facades in the future

Despite the specific characteristics and performance criteria of aluminium facade systems, the general approach of current building regulations means that curtain walling has to be treated as a traditional building envelope. A more considered approach, with thermal regulations and SAP/SBEM software specifically targeting curtain walling would shed light on these grey areas and foster the growth of innovation and best practice. Another positive consequence of this would also be that façade thermal engineering may develop into a less niche area of specialism which in turn would create a deeper pool of talent for recruitment and expansion.

Such change will ultimately be driven through increased awareness of the importance of thermal engineering and the realization of the specific part that façade systems play in reducing the overall carbon footprint of the building envelope. The continuous drive to reduce building CO2 emissions and create a greener environment will ultimately lead to an ever increasing value being put on façade thermal engineering departments.

Share and print content

Leave a Comment