24 THE BUILDING CONSERVATION DIRECTORY 2024 CATHEDRAL COMMUNICATIONS PASSIVE STRATEGIES EFFECTS Comfort Energy Efficiency Embodied Carbon Adjust internal uses in response to sun path, maximising daylight and solar gain Massively improved Improved No influence Using materials with favourable thermal-mass to minimise climate fluctuations Improved Massively improved Slightly worse Tackling any water ingress and water/ rainwater penetration Improved Slightly improved Improved Draught proofing windows to improve ‘air tightness’ and insulation Massively improved Massively improved No influence Using lime-based screeds and plaster to improve breathability at ground floor level and external walls Massively improved Slightly improved Slightly improved Enhance natural ventilation to prevent damp and improve air quality Massively improved Slightly worse No influence Bringing chimneys back into service Improved Worse No influence Retaining or using wood through the building’s fabric to lock carbon in Slightly improved No influence Massively improved Sealing off the chimneys while keeping top and bottom ventilated Slightly worse Improved No influence Arrange external spaces to suit outdoor activities in summer (shaded spots) and winter (sheltered spots) Improved No influence No influence Table 1: Effects of passive strategies on comfort, energy efficiency and embodied carbon level of intervention is necessary and indeed possible. The first step is to understand the significance of these properties and thereby the constraints in which work must be sensitively interwoven. There is then a chance to really begin to understand what might be achieved, whether it is changes around the fabric of the building, appropriate repair or modern retrofit. We also need to understand how these buildings have been built and how their fabric deals with moisture in particular, as most traditional structures need to breathe. This in itself presents a challenge when looking at improving the performance of these sensitive buildings. Carbon must be at the core of all our thinking. All our old heritage and listed buildings, whilst they will have the benefit of a significant lifespan, are essentially acting as stores for embodied carbon. We must therefore think very carefully about the improvements that we make or are required to make. Assessments of embodied carbon through carbon accounting can also allow designers and energy consultants to compare the different design strategies and approaches to redevelopment and upgrading, for example, light versus deep retrofit. In general terms, the case for refurbishment in short life buildings or those with a lifespan of 30 to 60 years is sound, as it will take many years for an efficient new building to draw level with an efficient refurbishment given the high energy and carbon required in new build. The same goes for older buildings, too, and by extending the life of our historic assets we can materially reduce the need for high carbon materials, technologies and activities. Historic England says that ‘the longer a building and its component parts last, the less embodied carbon is expended over the life of the building’, so, where required, repair, maintenance and upgrading will be the right approach in terms of keeping embodied carbon ‘locked up’. WHAT STRATEGIES CAN BE APPLIED TO HISTORIC PROPERTIES AND LISTED BUILDINGS? Given all the constraints, we know that the best results are delivered by retrofit practices taking a whole building approach using an understanding of a building in its environmental, cultural and economic context. This delivers balanced solutions that save energy and carbon, sustain heritage significance and maintain a comfortable and healthy indoor environment. This means a site-specific approach where opportunities and constraints can vary widely depends on context. A whole building approach makes use of passive and active strategies to achieve a truly sustainable renovation and upgrading of a building’s energy performance, while limiting embodied carbon emissions during retrofit, repairs and replacement. A passive strategy is one that capitalises on the natural elements of a site including sun and wind patterns to provide natural heating and cooling of spaces through the different seasons. An active strategy goes much further and relies on mechanical processes. These may involve adding new systems to generate energy, as well as incorporating improvements to the existing systems of the building. Passive strategies Passive strategies support a fabric-first approach to reduce the space heating demand by focusing on fabric improvement. There are a number of possible passive interventions applicable to a project. Not all may be applicable and some may be unnecessary or hard to justify financially or in embodied carbon terms, given their low impact. Table 1 illustrates a list of passive strategies that may be applied to historic buildings depending on their listed grade and specific constraints. Figure 1 (previous page) illustrates these interventions in the context of a typical architectural section of a listed property. Active strategies Given that most historic buildings have a greater reliance on their fabric for moderating their environment rather than on mechanical systems, then installation of active technologies can be challenging. However, their implementation can massively improve a building’s performance. Active technologies demand high capital costs and a noticeable increase in embodied carbon due to their manufacture and complex end of life disposal. For these reasons, systems should be selected and sized carefully to give value for money and achieve optimal performance. Figure 2 illustrates a range of active interventions in the context of a typical architectural section of a listed property. Some of these technologies may be impossible to install in a listed property while, for others, their application will require discussion and creative solutions so as not to compromise either the building’s historic fabric or damage its sense of place. For hot water and heating, one solution is the installation of heat pumps (ground or air sourced). Their technology is proven ACTIVE STRATEGIES EFFECTS Cost Energy Efficiency Embodied Carbon Air Source Heat Pumps Medium Massively improved Slightly worse Ground Source heat Pumps High Massively improved Slightly worse Hybrid boiler/Heat pump Medium Improved Slightly worse Biomass Low Improved Uncertain Hydrogen High Uncertain Uncertain Direct Electric Low Worsened Little influence District Heating High Worsened Uncertain MVHR High Massively improved Slightly worse Fireplace/chimney Upgrade* Medium Improved Little influence Table 2: Effects of active strategies on comfort, energy efficiency and embodied carbon * The fireplace/chimney upgrade includes installing tempered glass doors and a heat-air exchange system that blows warm air back into the room
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