Moving from building simulation to building performance

There is a long history of architects using empirical methods to test their design proposals, including physical models and prototyping, to help them understand potential performance outcomes. They rely on sound technical guidance when making design decisions, and use carefully constructed simulations to model how their buildings will perform (under particular conditions and use scenarios).

Yet post-occupancy evaluation (POE) shows that many buildings underperform on energy use, often by a factor of four, as the evaluative tools used may not be sufficient to resolve the complexity of the whole building. This difference between predicted and in-use energy consumption, often called the performance gap,¹ is becoming a key issue for clients and the design team, although POE has yet to become mandatory through Building Regulations. Clearly a critical approach to technology is essential to ensure that architecture performs well.

Sarah Wigglesworth Architects’ exemplary primary school, Sandal Magna, demonstrates a unique attempt to ‘demystify’ the way the building works; visible environmental technologies are designed into the building to help occupants and visitors to read and use the building as a whole. The relationship between building and users has led to it being cherished, while also acting as a learning tool. Despite this, the complex technology employed at the school, and its command centre – the building management system (BMS) – have failed to perform as intended, due to a lack of adequate guidance and aftercare compounded by contractual difficulties. Such issues must inform a critical approach to the usability of technology, especially when recommending relatively complex technologies to clients and users. The move to a more holistic understanding of building performance represents a departure from more simplistic simulation of single issues.

Monitoring to socio-technical evaluation

Architects have always recognised the relationship between buildings and people, but it is only recently that they have begun to appreciate – based on the collection of sound evidence – the scale of the impact of human behaviour on actual building performance. At the ground-breaking BedZed development in Hackbridge, London, monitoring over the first seven years post-completion showed a twenty-fold variation in energy use for exactly the same housing design.² These types of studies have led a number of practices, such as Anne Thorne Architects, to actively adopt building performance evaluation methods which take account of people’s attitudes and behaviour, in addition to the usability of the building itself.

Fabric performance standards

Another relatively recent change has been the increasing emphasis on improving the performance of the fabric of buildings. In the last few years an increasing number of practices have adopted the Passivhaus approach. Originating in Germany, the Passivhaus standards combine increased airtightness with high insulation standards in the building envelope, and controlled mechanical ventilation heat recovery systems.³ The jury is still out on how resilient these technologies will be over time, but early performance evaluations have been very positive.

Other practices, such as Stride Treglown, are actively investigating the use of naturally hygroscopic materials (such as lime and hemp) to increase comfort, minimising the need to resort to mechanical air conditioning. New research and understanding of the building physics of natural materials is leading to an increasing interest in low embodied energy solutions for construction.⁴

Climate change mitigation and adaptation

Climate change prediction and modelling software⁵ is becoming increasingly available and has the potential to be a game changer, offering practices – such as Bauman Lyons Architects (BLA) – the opportunity to future-proof their designs by factoring in predicted increases in temperature and extreme weather events, such as storms and flooding. By dealing with climate probabilities (rather than specific design constraints) this approach accepts a degree of uncertainty and leads to robust design solutions that can accommodate a range of different futures. It can be used to ensure that both new-build and retrofit projects are to remain fit for purpose.

BLA have made a commitment to do environmental modelling during the early stages of design, and aim to ensure that their design work is underpinned by a firm understanding of the building physics involved. This is something that all practices will need to do if they are to fully engage with the implications of our rapidly changing climate.

Economic life-cycle costing to whole life-cycle costing

The proportion of a building’s total (embodied and in-use) energy consumption that happens before the building is even occupied can be between 30 and 70 per cent – and this has led to an increasing interest in moving from purely economic life-cycle costing to whole life-cycle costing, which includes embodied energy/carbon as well as other environmental impacts. These are methods that Stephen George & Partners have been investigating in their study of materials for ‘commercial’ projects. Despite increasing interest, there are no mandatory requirements to undertake this type of evaluation in the UK, although there is strong lobbying for change with proponents noting that whole life-cycle costing is routine in countries such as the Netherlands.⁶

Soft Landings and BIM

The last major change in technology is the advent of building information modelling (BIM) and the complementary Soft Landings process. Whereas BIM allows those involved to fully coordinate all aspects of building information over the building’s whole life cycle, Soft Landings aims to help solve the performance gap.⁷ The government is committed to applying Soft Landings through Government Soft Landings, mandated from 2016.⁸

Standards, simulation and the need to synthesise

Using technology successfully in architecture involves strategic briefing and the careful choice of performance targets, usually with the intention of meeting particular standards. While the choice of target standards is ultimately related to the client’s ambitions, architects may influence the decision. Many practices prefer the BREEAM assessment as their benchmarking standard of choice, while others are increasingly adopting (and being employed because of their experience in meeting) standards that are more rigorous, or that focus on a particular aspect of performance. Like many practices, Anne Thorne Architects work to Passivhaus standards and use the related Passive House Planning Package (PHPP) spreadsheet tools during design.

While some standards have their own related tools, often the next step after standards are decided on is to choose a suitable building simulation software package, such as CarbonMixer,⁹ which will allow preliminary morphological choices to be tested against predicted carbon emissions. Frequently a different package will be needed later in the design process in order to test and refine design proposals and predict overall energy and carbon use.

Selecting a detailed simulation is not always easy – there are many to choose from, and not all software is particularly user-friendly or well integrated with other design tools. However, judicious use of environmental software with climate change prediction tools, such as Integrated Environmental Solutions (IES) – as used by BLA for developing their future-proofed retrofit solutions, can pay huge dividends in terms of providing evidence to inform current design making. Nonetheless, through research associated with their modelling, BLA have identified numerous shortcomings with thermal simulation in relation to thermal adaptation strategies, which they have had to overcome in order to produce resilient solutions.¹⁰

Bucholz McEvoy Architects have taken their analysis further, and have developed a process which allows them to better synthesise their technical research. They know that with many design solutions come increasingly specific performance criteria relating to individual building elements and therefore use a matrix which allows them to make comparative judgements across multiple modes of working, recording data and criteria, to help ensure that they use technology holistically.

Embodied performance

Stephen George & Partners have taken a novel approach to assessing the various embodied factors contributing to fabric performance. Having identified the typical environmental criteria related to the whole life-cycle costing of materials, they go on to examine two factors they deem most important (embodied energy and carbon emissions) against other commercial factors such as delivery time, training requirements, potential product failure and financial risk. This allowed them to pragmatically rule out a number of materials for their case study building that had originally seemed environmentally promising. They also came to the conclusion that it was extremely difficult to obtain answers from manufacturers, suppliers and trade organisations and that it was unlikely that a single quantified answer could ever be arrived at. This is an interesting viewpoint, and one very much at odds with conventional evaluation tools, such as SimaPro or the BRE Green Guide to Specification.¹¹ It is also, perhaps, more honest, as it acknowledges the impact of context and location – something rarely present in typical life-cycle evaluation. However, the downside is that it is impossible to know how rigorous their evaluation actually is due to the ‘swings and roundabouts’ approach that effectively results in qualitative trade-offs. A truly comprehensive tool for materials selection, one that integrates both quantitative and qualitative issues, remains a holy grail.

Embodied energy is not the only aspect of building materials that requires research. Other aspects of the performance of materials include thermal properties; Stride Treglown are meticulous in their measurement of the thermal conductivity of materials, using desktop methods to predict the U-values of construction elements while monitoring performance through temperature and humidity data loggers. This allows them to analyse the performance of the insulation panels they have developed.

While none of the case studies in this section of the book has mentioned the use of thermal imaging cameras or airtightness testing, these are another two useful methods available to practices. Although not totally foolproof, they do give fairly quick answers about performance, flaws, and whether design intentions are being realised.

Building performance evaluation

Several of the case studies in this section have successfully utilised building performance evaluation (BPE) methods¹² to understand the performance of their projects in reality, and improve their future. BPE is different from POE in that its methods can be used at any stage of the building life cycle – not just after occupation – to inform future design and performance.¹³ Unfortunately POE does not automatically result in performance improvement and, sadly, unless built in from the start, many studies are bolted on at the end, and their results may end up on the shelf. However BPE, or planned POE, can lead to useful findings.

Anne Thorne Architects used a variety of POE methods, including occupant surveys and environmental monitoring, to establish how well their design intentions were realised at Angela Carter Close. A key finding for them was about the importance of specifying environment controls for buildings that are more user-friendly. Stride Treglown Architects and Bucholz McEvoy Architects went one step further and investigated fabric design solutions by using BPE methods to improve performance directly.

Stride Treglown used careful experimental monitoring to test a new form of retrofit panelling. Bucholz McEvoy integrated BPE methods alongside prototyping and physical models to develop a bespoke timber facade for natural ventilation purposes. However, neither practice mentions evaluating the installation and commissioning stages: this can be critical when relating design intentions to actual performance.