Essay 4
Designing low-energy buildings
Simon Bradbury, Plymouth University
Architects and designers are uniquely placed to take a central role in addressing the performance gap and delivering low-energy buildings. However, currently there are only a limited number of practices that have the expertise and are participating in post occupancy evaluation (POE) of their own projects. A recent survey suggested that only 3% of architecture practices undertake POE on their own housing projects.29 Therefore the profession is not able to feed back and build virtuous circles of learning.30 This chapter outlines why architects and designers are well placed to take this lead, and how they can develop their own processes of design and feedback.
Developing skills and knowledge
The first challenge faced by architects is developing the skills and knowledge necessary for energy modelling. Energy modelling is not typically an activity undertaken by architects because of the way it is procured. It is usually done by an independent consultant who will be primarily concerned with ensuring compliance with Building Regulations – and not with informing design decisions, optimising performance or developing accurate predictions of final energy use. This separation of function results in architects and designers not being directly aware of the consequences of design changes on energy performance – or, worse still, being hostage to compliance models late in the design process.
01 Change in heat loss parameter (HLP) in a house, from design to occupation
If you look at energy performance in buildings it changes throughout the design process as a result of variations to the form and specification of a developing project. This is clearly illustrated in Figure 01, which shows how the energy performance of a house changed from initial design to occupation. The graph plots the change in the heat loss parameter (HLP), – loss divided by floor area – with each change explained in Table 01.31 The graph also illustrates the changes in HLP derived from the regulatory model – the Standard Assessment Procedure (SAP). It is evident that there is significant variation in the design performance, particularly in the early design stages, relative to the as-built performance. It is also clear that there is a large discrepancy between the regulatory model (SAP) and the design performance throughout the project. Although this is only one project, the changes that have taken place in the design process are not unusual (for example cost, design coordination and compliance with regulations). This is because many design decisions impact on issues such as geometry, airtightness, M&E systems or the thermal performance of the fabric. Energy performance should therefore be seen as one of many other considerations (social, economic and regulatory) that shape the design of a building. This means that in order to manage the energy performance through the design process it is necessary to be able to update the energy model alongside variations in design, and not have a ‘gap’ between the design and energy model as in this example.
The separation of energy modelling from the design process therefore removes the ability to easily negotiate energy performance in the context of other issues. This is made more problematic when the model being used is a regulatory compliance model such as SAP, which is neither a design tool nor intuitive to use, and whose outputs are difficult to connect with design decisions.
Integrating energy modelling into the early design process, when decisions about massing, orientation and fabric are made, is particularly important. In Essay 3 Gething highlighted the importance of the early design stage in minimising the performance gap. The opportunity for architects is to develop capacity to undertake energy modelling as part of early design decisions, to allow for the optimisation of the building. This will also allow for a more integrated understanding of performance, as the complexity of projects develops over time. It will also support a collaborative relationship with the design team, engineers and contractors to ensure that early principles are carried through.
Many architecture practices have been drawn to use the Passivhaus Planning Package (PHPP), a spreadsheet tool for designing Passivhaus projects, as one way to develop this capacity. Despite its complexity the tool allows designers to understand the impact of decisions on performance. The recently launched three-dimensional plug-in to SketchUp further enhances this tool, by allowing architects to integrate energy performance into their normal workflows. This tool, along with others, offers significant potential for architects to engage with low-energy design early in the design process. It also helps to build an appreciation of the many other factors, such as services, thermal bridging and airtightness, that influence the delivery of a low-energy building and help to minimise the performance gap.
Managing the design process
In addition to developing skills and knowledge it is also important to be aware of a number of common areas where decisions in the design process are likely to impact on performance.
Changes to the design brief are common, particularly in the early design stages when different overall design strategies are being considered. However, attention should be given to how this affects the compactness of the building form and orientation. For example, the PHPP encourages designers to focus on a compact form and good solar orientation, which contributes significantly to the ability to design a building that achieves Passivhaus standard. Compact building form and careful orientation go a long way to reducing total energy consumption of buildings.
Cost control and value engineering can have a significant impact on performance. The changes can vary from the more obvious, such as product substitutions, to a lower-performing thermal element (e.g. window or insulation material), to the less-obvious such as changes in geometry or specification of different M&E systems. This happens throughout the design and construction of a project, but can be particularly difficult to manage once a building is on site. It is important that architects are aware of which changes will impact on energy performance, and that these are communicated between the design team, contractor and client to enable the impact of any changes to be understood as part of any value-engineering process.
Specification and design of construction systems and products, particularly where they are complex or involve off-site manufacturing, can impact on design performance and contribute to the performance gap. Problems can arise when a system or product performance is based on a typical condition, and not on the specific design proposal. For example, the thermal performance of timber panel systems may be based on an assumed amount of timber content and not on the actual design solution, leading to unexpected changes to the performance late in the design process. Worse still, these changes may not be recognised until after construction. In addition, there needs to be careful consideration of the design of junctions between systems to ensure continuity of airtightness and thermal performance, as well as sequencing of construction. It is important therefore to work with suppliers to ensure that the assumptions about the performance of a system are robust, and that they are updated as the design develops.
Sequencing and design coordination must be considered early in the design process. This may include strategies to effectively install insulation and airtightness membranes, or the installation of services and penetrations through the thermal envelope. It is important to consider when, where and how services will be installed during the construction process. All too often, particularly in house building, this is left to decisions made on site. This can affect the efficiency of systems such as mechanical ventilation with heat recovery (MVHR), and also the airtightness of the building fabric. Other common issues relate to thermal bridges and airtightness at junctions, which can be affected by the sequencing of construction or tolerances of different building materials.
Regulations and standards, including those that are not related to energy, can also impact on performance. For example the incorporation of accessibility or fire regulations may change the geometry of a building, affecting its compactness or complexity. Alternatively planning constraints on overlooking or rights to light may impact on solar gain. Many of these regulations are requirements, and therefore consequential design changes may be needed, such as increasing thermal performance in other areas, to compensate for any negative impact that results from their incorporation.
The first steps to BPE
Developing a better understanding within a practice of energy performance and the issues that impact on it is often the first step to undertaking BPE. If you have an appreciation of the issues that impact on energy, it is easier to look for these in a completed project. However, undertaking BPE can still be a challenge for an architect who has not done it previously.
In this context, developing a range of partnerships with universities offers some opportunities. The Standing Conference of Heads of Schools of Architecture in 2015 was specifically about incorporating building performance evaluation into the curriculum and, with the RIBA soon to be updating its validation criteria, this presents a good opportunity to rethink how young architects engage with the evaluation of buildings.32
There are already a number of courses, particularly at postgraduate level, on which students learn about and undertake BPE.33 Although further consideration needs to be given to how to integrate BPE into undergraduate teaching, and particularly into the design studio, these courses may present opportunities for practice. For example, having a number of undergraduate students study a completed project may offer valuable insights both for students and practices.
There are many examples of this being done on individual buildings, where students monitor energy and interview occupants and the design team. Getting students to engage in BPE will create future practitioners with the interest and understanding to undertake this work. This of course calls for both university and practice to develop more collaborative models of teaching, which is indeed in line with current thinking on the future of education.34
Student projects do not need to be limited to studying individual buildings; they could evaluate other aspects of practice. One example is the work of the Plymouth University students who undertook daylight analysis of 900 award-winning housing schemes using a tool called LightUp. They were able to show that many projects were not meeting regulatory guidance for minimum daylight in homes. This revealed a systemic problem in regulation and practice, but also supported students in designing their own studio projects with a much more sophisticated approach to daylight.
These initial partnerships through teaching offer the potential to develop into more significant research collaborations of the sort described in the following two chapters, and exemplified by some of the case studies in this book. However collaboration between academia and practice is also valuable in that it ensures a level of independence in the evaluation of projects and, importantly, the obligation and mechanisms to disseminate findings.
Building collaborative models between teaching, research and practice therefore presents a clear opportunity for practice and academia, in an environment of increasingly competitive research funding and in a profession that needs to build a stronger evidence base that demonstrates the value of architects.35
Conclusions
Increasingly, practices that are engaged in low-energy buildings are building project teams that have an integrated understanding of the issues related to energy and are working across projects to improve their own practice. (Many of these practices are included as case studies in this book.) It is clear that where this is the case, lessons are being learned and fed back into the design process. However, much work is needed to encourage this across industry.
Where practices are learning from their own projects they will increasingly be able to work with clients to support them in mitigating the risk of underperformance by managing the process of design. In these instances the management of the energy performance of buildings could be viewed in a similar way to the management of the risk of overspend. In the early design stages, where there is significant uncertainty about the design of the project, the potential risk of under-performance will be high, along with the variation in the predicted performance. However, as the project is developed the variation of the predicted energy performance would reduce, as well as the risk of a performance gap. Figure 02 is a diagram of how this might be understood, illustrating each stage of the design and construction of a building. This approach should enable a more critical understanding of how to manage energy performance in buildings, while recognising that it is not an exact science.
Finally, developing a culture of feedback on projects should also be about broadening the issues and methods we use to evaluate buildings. In this book the focus is on energy in the context of social and technical challenges, and on how to close the performance gap. However, evidence is needed across a range of other areas – and architects, in collaboration with academia, have the potential to uncover this.
02 Graph detailing performance variation from operational energy performance by construction stage
Building performance evaluation – where to start?
1 Build internal capacity
Architects should build internal capacity to enable a better understanding of energy issues in the context of design. This will also enable them to work collaboratively with those producing the building energy models from the outset of projects, and to work with clients and contractors to integrate this through the design of a project.
2 Keep it simple
Do not be over-ambitious with complex buildings and monitoring processes. Low-energy buildings are becoming increasingly technically complex, and systems and building complexity have been shown to have an impact on the reliability of performance (see Essay 2). It is also not necessary to embark on complex evaluation processes; simple questionnaires and walk-rounds are a good start to uncover many issues.
3 Learn from your own projects
The practices in this book have all started in one way or another by looking at their own projects as a source of learning – including, in many cases, the monitoring of their own offices. This might also involve developing or improving existing project feedback systems. These initial exercises offer a low-risk way of testing and learning about new technologies and processes.
4 Seek partnerships
In the longer term, partnerships with academia, other architects and consultants offer the greatest potential to access additional resources, and also collectively address the issues you are interested in. These could start in a relatively small way on a single project and then grow over time.
5 Publish your findings
Although the findings that emerge from your own projects will be of benefit directly to your future work, practices that have engaged in BPE have found that publishing their findings provides them with credibility among clients and in the wider profession.