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To decarbonise the built environment, it is widely assumed that ‘fabric-first’ building upgrades are essential. An alternative, people-first approach is proposed that could deliver energy and carbon reductions at scale and speed. The approach begins by re-examining some rarely questioned assumptions around historical practices and building science. Physics and thermal physiology can inform a reassessment of the causes of thermal discomfort, and show why using air temperature alone as a measure of the thermal environment is inherently problematic. Historical sources reveal the forgotten ways people were made more comfortable in the days before space-conditioning. Together, these encourage a deeper examination of how buildings were constructed, maintained and operated prior to the Industrial Revolution. These insights can be harnessed to develop a practical new trajectory for building operation and retrofit. Preliminary results are reported from two ongoing UK field studies. Co-creation workshops and simple environmental monitoring are being used to encourage occupants to learn to ‘sail’ (i.e. passively manage) their own buildings more effectively to support their own needs. It is not yet possible to put numbers on the energy and carbon saved, but these early experiments may encourage professionals and policymakers to give much greater consideration to ‘people-first’ climate action. Policy relevance A common approach to decarbonising buildings is a focus on ‘fabric-first’ retrofits, which tend to be disruptive, carbon-intensive, expensive and will take decades to convert the stock. Feedback is also exposing disappointing savings, and risks to both building fabric and occupant health. This approach often seeks to update buildings to ‘modern’ standards, using models that have proved problematic, and frequently ignoring in-use performance. Conversely, a ‘people-first’ approach can empower occupants to identify what might improve things, trial simple interventions, and make rapid, low-risk alterations to improve their health and thermal comfort. This can draw on and adapt proven, low-cost historical methods. This alternative ‘soft’ approach uses facilitators to help occupants ‘learn to sail’ (i.e. effectively operate) buildings more effectively and sustainably. The insights will also enable any capital measures to be more precisely targeted.

The path we are currently following towards ‘sustainable design’ is a result of the accidents of the past 300 years of history. If we look further back, to before the exploitation of fossil fuels, we find a very different approach to building envelopes, and to building use and comfort. This was necessarily very low carbon, and demonstrably effective, but, unfortunately, we have forgotten many of the fundamental principles on which it rested. This paper argues that our current choice of retrofit pathway is leading us away from, rather than towards, a sustainable built environment. Current efforts to reduce carbon and energy based on modern ’layered’ envelopes and misunderstandings of thermal comfort are proving much less effective than predicted. We would further argue that they are too often delivering unintended consequences: contributing to the overuse of carbon and energy, and derailing the development of a sustainable built environment. We draw on research and case studies, as well as on the lessons from history, to show how the problem derives from a neglect of first-principles thinking and fundamental building physics. Equally, though, we show how combining good building physics with a re-evaluation of older approaches to construction and building use delivers some powerful and effective tools for tackling the climate emergency.

The climate crisis demands an urgent societal shift, and the UK government has responded with a strong policy targeting energy retrofit to improve the energy performance of homes to achieve the net zero target by 2050. However, research has shown that standard retrofit measures have resulted in undesirable unintended consequences. Incorrect interventions such as using incompatible materials can affect the equilibrium of the building, increasing the risk of surface and interstitial condensation due to excessive humidity levels. Mould growth may develop under high levels of humidity, damaging the building fabric but also posing a risk to the occupants; it has been linked to asthma exacerbation and other respiratory infections. Therefore, what is needed is a well-integrated retrofit approach that not only reduces energy use but protects the building and the health and well-being of its occupants. This paper discusses the retrofit practices, the main challenges that retrofit practitioners face in the UK, and which guidance and tools they work with through the lens of the impact on occupants. A deeper understanding of the current practices is needed if those unintended consequences are to be avoided. For instance, replacing a 'fabric-first' mindset with a 'people-first' approach that considers more factors like the causes of thermal discomfort, and the gains to be made from passive and adaptive comfort approaches, could contribute to deliverer energy and carbon savings and increased building's indoor environment quality and usability justified.

Demands on buildings continue to increase: energy reduction, maintenance simplification, climate change adaptation, new ideas about comfort and modern patterns of use. It's often thought that these must be in fundamental conflict--but if you get things right, then it's usually fine all round. The key is to think holistically, concentrating not just on the building's fabric and context or its services, but on the occupants as well. At Historic England, we call this the building performance triangle: you can't address the fabric in isolation from the heating, cooling and plumbing. Housing and offices face similar issues: there is a huge gap between the energy performance promised by computer modelling and what is actually provided, and we also know that highly conditioned spaces are often too hot and poorly ventilated.

Building professionals often propose using water-resistant coatings to protect walls of masonry and other permeable materials, especially after devastating events such as floods. The effectiveness of materials such as stone, timber, brick and lime mortar lies in the very fact that they are water-permeable -- that is, they have an open and connected pore structure through which water can travel. Traditional construction also incorporates details such as eaves, hood mouldings and footings to protect weak points where water might collect and be drawn into the wall, though maintenance remains critical to its performance. The lesson is that treatments need to be tested outside the lab, and for longer periods. It is not enough to show that a coating can slow initial water uptake: other consequences need to be investigated, especially over the life of the building.

Practical Building Conservation was one of the earliest projects of the Research and Technical Advisory Service of English Heritage. Tasked with providing government and wider sector support for the conservation of the historic built environment, team leader John Ashurst decided that the most effective approach would be to rework the field notes from his conservation team in the Ministry of Works into a series of technical guides. Conservation Basics, Concrete and Roofing followed in 2013, with Building environment published in September 2014. The last of 10 volumes, Earth, brick and terracotta, will finally be published in July this year, by which time the technical side of English Heritage will have become Historic England. The first thing to note is that the books do not prioritise treatment: intervention choices must always be case-specific, and so to print anything resembling a specification would be dangerous.

Practical Building Conservation was one of the earliest projects of the Research and Technical Advisory Service of English Heritage. Tasked with providing government and wider sector support for the conservation of the historic built environment, team leader John Ashurst decided that the most effective approach would be to rework the field notes from his conservation team in the Ministry of Works into a series of technical guides. Conservation Basics, Concrete and Roofing followed in 2013, with Building environment published in September 2014. The last of 10 volumes, Earth, brick and terracotta, will finally be published in July this year, by which time the technical side of English Heritage will have become Historic England. The first thing to note is that the books do not prioritise treatment: intervention choices must always be case-specific, and so to print anything resembling a specification would be dangerous.

Water is critical to many of the familiar deterioration processes that affect historic buildings, but much of the picture describing how moisture accumulates and distributes itself within materials has been developed in fields outside conservation, and even outside building engineering. In the course of a more-or-less chronological literature review, this paper presents a summary - which is largely nonmathematical - of the current understanding of moisture behaviour in building systems composed primarily of brick, stone and mortar. From considering why porous materials attract moisture in the first place, and the principles behind how transport processes such as wetting and drying are mathematically modelled, the review moves on to look at the additional theory necessary to handle complex building materials and systems. After a short discussion of some building-scale processes such as rising damp, the paper concludes with a summary of some of the issues that remain unresolved.