EnerPHit

A Step by Step Guide to Low Energy Retrofit

James Traynor

• Publisher: RIBA Publishing
• Year: 2020
• ISBN:
  9781000706819
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture générale

In order to meet UK Carbon reduction commitments for 2020 and 2050 building owners will be required to upgrade their buildings to meet an increasingly stringent set of energy performance requirements. In the absence of any clear advice from UK Government on how this can be achieved, the EnerPHit standard offers a very clear methodology. This is a practical guide that gives architects the tools to retrofit buildings to the highest EnerPHit standard. It equips the reader with the key information on EnerPHit (as the most effective benchmark for performance), the practical know-how and tips to ensure effective retrofit throughout all Plan of Work stages of a project to the EnerPHit standard. Backed with real-life case studies, it enables you to understand how to achieve successful outcomes tailored to suit available budgets and programmes.

1.0: Introduction

1.1: PURPOSE

This book considers the importance of building refurbishment and the Passivhaus EnerPHit standard as a means of achieving improved thermal comfort for building users and reduced carbon emissions in the building sector. Both are vital in order to meet the international targets set out in the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Climate Agreement of December 2015.

Much has been written on the importance of Passivhaus. Developed in the early 1990s by academics Bo Adamson (Lund University, Sweden) and Wolfgang Feist (Institute for Housing and Environment, Darmstadt, Germany), the first Passivhaus building was created in 1991 in Kranichstein, Darmstadt. With tens of thousands of completed projects around the world and clear evidence from these that performance in use closely matches the design model, it has since become recognised as the gold standard in building performance. Passivhaus was originally developed as a voluntary standard, but has now been adopted by many local authorities as a means of both reducing carbon emissions and ensuring buildings perform as designed.

However, much less has been written on the application of Passivhaus to existing buildings. The first existing building to be refurbished to the Passivhaus standard was the Ebok office building in Tubingen, Germany, completed in 2003. Following these early refurbishment projects by the Passivhaus Institute (PHI) in Darmstadt, Germany developed the EnerPHit standard in 2010. It employed the same energy performance methodology but, in recognising the difficulty of refurbishment, would accept a marginally lower standard. For example, in an existing building it may not be possible to insulate the ground floor or basement level, and it can be extremely difficult to change the orientation of the building or significantly alter the building form. Therefore, alternative methods need to be employed to improve the building fabric and reduce heat losses. Nevertheless, the performance standard for refurbished buildings is still significantly better than typical newbuild standards in most countries.

This book recognises the benefits and challenges of EnerPHit as a means of achieving improved building performance, and shows how this has been applied to a series of building typologies around the world. Passivhaus – and more recently EnerPHit – has been most widely applied in the domestic housing sector, with many examples in the UK alone; however, there are relatively few examples of EnerPHit applied in non-domestic sectors. A range of building typologies and projects from around the world have been selected as case studies to represent both the challenges and opportunities for deep retrofit to the EnerPHit standard. These case studies include a church, university, commercial bank, affordable housing, sheltered housing, student housing, private owner-occupied housing and private rented housing in a listed ‘heritage’ building. In each case, the standard EnerPHit methodology was used to inform the performance target, with individual challenges that required a specific response in design, delivery and execution. Where available, pre- and post-retrofit studies that were undertaken by the project team or third parties to demonstrate actual performance against targets have been referenced.

While this book is primarily addressed to architects, engineers, surveyors and contractors, it is also written to inform both building owners and policymakers of the benefits of EnerPHit to improve performance and reduce carbon emissions. Building owners with a long-term interest in their assets need to understand the impact of this methodology in terms of improved comfort and reduced running and maintenance costs, alongside the impact of the physical works and capital cost. Policymakers seeking to implement carbon reduction targets for 2050 must also understand the importance of this rigorous methodology and the need for consistent support, advice and legislation to enable building owners to achieve these targets.

While only two of the eight case studies presented are in the UK, the background issues and implications of EnerPHit are primarily applied to the UK context and important lessons are drawn from other countries, most notably Germany, which has the highest uptake of EnerPHit projects. Alternative local or national methodologies are also referenced for measuring energy performance and contrasted against the Passivhaus methodology to understand relative benchmarking both in design and in use.

Significantly, there is feedback from the building users – perhaps the most important aspect of a successful retrofit. Many questions are considered in each case, and feedback gathered to inform future retrofit projects. Were the building users involved in the design development of the project? Did the building users remain in occupation during the works, and was this successfully managed? Are they satisfied with the outcomes of the retrofit? Does the building perform as designed?

Unlike newbuild projects, retrofit schemes benchmark against both existing energy performance and existing thermal comfort. In EnerPHit schemes this means significant improvement in both measures, but a fair comparison would assume that the existing building was heated, cooled or ventilated to adequate levels, e.g. World Health Organization thresholds. If that were the case, the percentage reduction in carbon emissions or energy bills would match modelled expectations. However, in many cases, this is not the reality. The very reason for the retrofit may be due to the poor thermal comfort, perhaps caused by fuel poverty and the inability of building users to adequately heat the building. As a result, the building users are able to adequately and affordably heat, cool and ventilate their building but it can cause a ‘rebound effect’ (also known as the ‘Jevons paradox’) which reduces the theoretical carbon savings and environmental benefits.

This rebound effect can apply to a diverse range of building types, as described in the case studies for Wilmcote House and Sparkasse Bank. While this rebound may include legitimate improvement and does not necessarily affect performance against the EnerPHit standard, it should nevertheless be considered when estimating the potential benefits of wider application and carbon reduction targets. Pre-retrofit evidence¹ from Wilmcote House clearly demonstrates the need to understand actual energy consumption rather than estimated consumption.

Finally, the conclusion considers the evidence from the case studies and other relevant data compared against the global and national targets for carbon reduction by 2050, considering the practical challenges and the means of overcoming these in a ‘step-by-step’ retrofit plan over the next 30 years. It also reflects on the benefits of a widespread retrofit programme to the EnerPHit standard, and how this compares to current targets (or lack of) for the improvement of existing buildings, other refurbishment initiatives and the wider social and health benefits to building users.

1.2: BACKGROUND:

There are around 27.1 million dwellings in UK, 80% of which will still exist in 2050.² At present these dwellings represent approximately 27% of UK CO₂ emissions.³ Almost 40% of housing in England pre-dates 1945,⁴ and about 15% of the UK’s CO₂ emissions can be attributed to the burning of fossil fuels to provide space heating in housing.⁵ As current rebuilding rates are delivering only approximately 120,000 new homes per year, we clearly cannot rely on newbuild to deliver the seismic shift needed to achieve the targets set by the Climate Change Act 2008. Neither can we rely on demolition of the worst-performing stock. The acute housing shortage in the southeast of England⁶ and the partial failure of the Pathfinder scheme⁷ in the northwest of England show in different ways that we cannot demolish and rebuild our way out of this problem.

Retrofit is distinctly different to refurbishment or repair, which have traditionally been the methods used to treat existing buildings. This has generally been either for essential maintenance purposes or for cosmetic reasons, to update or modernise the appearance of the building. Instead retrofit aims to upgrade an existing building to meet wider objectives: reducing energy consumption and improving thermal comfort. Retrofit also typically includes other works, including essential maintenance and improvements to the aesthetic appearance of the building, which are carried out at the same time.

Retrofit is typically cheaper than demolition and rebuild. While there may be other reasons to consider redevelopment, such as increased density, it is usually more cost-effective to refurbish. The questions then become how to retrofit, to what standard, and how can this be done with building users in situ? If we consider the targets set out in the Climate Change Act and subsequent international agreements such as the Paris Climate Agreement (2015), existing buildings need to be ‘zero carbon’ by 2050. But if af all existing buildings were upgraded to be zero carbon, this would mean that over 2,000 buildings per day, every day, until 2050 would need to be upgraded to meet this target.

1.3: ATTEMPTS TO RETROFIT

There is much to be done over the next 30 years. If we are to have any chance of achieving these targets, the work needs to start now.

In recent years, the UK government has attempted to leverage change and encourage retrofit through initiatives such as the high-profile, but ultimately unsuccessful, Green Deal scheme. The failings of this scheme are well documented both in the uptake, cost-effectiveness⁸ and the quality of installations carried out. Indeed, this author was involved in the largest Green Deal scheme and saw at first hand the impact of piecemeal measures and poor-quality installations. Following the closure of the Green Deal scheme, the UK government commissioned Dr Peter Bonfield to lead a review⁹ into the failings of previous retrofit schemes and provide recommendations for the future. The recommendations in the ‘Every Home Counts’ report included ‘cross-cutting’ themes including the following:

• Consumer protection
• Advice and guidance
• Quality and standards
• Skills and training
• Compliance and enforcement

It also included sector-specific themes:

• Insulation and fabric
• Smart meters
• Home energy technologies
• Application to social housing

Under ‘quality and standards’, the review recommended the development of an overarching standards framework for end-to-end delivery of retrofit measures. The existing code of practice and specification for installers of energy-efficiency measures (PAS 2030) was particularly criticised as not fit for purpose, and this document has subsequently been rewritten by industry experts. An updated version was released in 2017, which requires three fundamental principles to be followed as described below:¹⁰

• Designers are to provide an adequate and site-specific design for each installation, and no installation may proceed without a design. Installers are to check the design is satisfactory before installation, referring back to the designer where amendments are required.
• Designs and installations must have a ‘whole-building focus’, with understanding of the interaction between different building elements, both physical junctions (such as wall to roof details) and technical relationships (such as airtightness and ventilation strategy). This strategy should include measures that may already be installed, those that are being considered as part of the works, and those that may be undertaken at a future date.
• When upgrading insulation, the impact on ventilation must be considered. Background ventilation must be provided via trickle vents to all rooms, and extract ventilation provided to ‘wet rooms’, i.e. kitchens and bathrooms. Where multiple measures are installed and deep retrofit achieves airtightness levels lower than 5 m³/m²/hr at 50 Pa, all rooms must have ventilation via air inlets with extraction from wet rooms.

These seemingly obvious requirements were not stipulated under previous retrofit schemes. In conjunction with the development of a new ‘EHC (Every Home Counts) Quality Mark’ equivalent to the Microgeneration Certification Scheme (MCS) for renewable energy installations, it is hoped that these recommendations and the forthcoming PAS 2035:2018 (specification for the energy retrofit of domestic buildings) will result in a more comprehensive, holistic approach to future retrofit.

1.4: NEWBUILD STANDARDS

It is well known that buildings are typically designed to meet, rather than exceed, statutory performance requirements. While some clients choose to target higher standards, it is not the norm. Building regulations in all countries tend to increase requirements over time, which means that older buildings typically perform to a lower standard. As a result of the 2002 EU EPBD (Energy Performance of Buildings Directive), standards for energy performanc...