The Building Conservation Directory 2022

100 T H E B U I L D I N G CO N S E R VAT I O N D I R E C TO R Y 2 0 2 2 C AT H E D R A L COMMU N I C AT I ON S FEELING THE DRAUGHTS Air-infiltration in traditional buildings LILA ANGELAKA and ROGER CURTIS O LD OR traditionally constructed buildings (often described as ‘pre- 1919’) are sometimes considered draughty and hard to treat. Figures for the exact number of traditional buildings vary, but in the UK, it is around 19 percent of the domestic housing stock. In historic town centres the figures are much higher. With so many older buildings there is an obvious imperative for them to contribute to mitigating the impacts of climate change. This can largely be achieved through reducing operational carbon use to reach the various national energy saving targets. Reducing CO 2 emissions within the existing building stock can be achieved through retrofitting to improve their energy performance, and a key aspect of this is managing air-infiltration in the building fabric. Besides the obvious changes to our perceptions and expectations of thermal comfort today, in older buildings excessive air infiltration often indicates an accumulated lack of maintenance or a combination of repairs and changes which may exacerbate existing issues. By addressing these issues and with some moderate adaptation, the building fabric can be made more airtight as part of the approach to increase energy efficiency. However, modest amounts of ventilation are also necessary for both the health of the building and its occupants. So, when considering work to address air infiltration in a traditionally constructed building, it is important to understand how that building was originally designed to work. In the past, buildings were designed with natural ventilation in mind, which ensured air flow around building elements, helping disperse water vapour and keeping the fabric free from excessive moisture and the consequent risk of decay. This was achieved by allowing modest air ingress and outward movement through vents, windows, doors, and chimneys. It is understood that much of this air movement was deliberate, as open fires needed incoming air to draw properly. Such ventilation should never be fully eliminated but reduced to acceptable levels. Some of these ventilation pathways are shown in figure 1. The general approach to ventilation in older buildings has been covered by Historic Environment Scotland (HES) in a recent Inform Friday seminar, and a link to this is at the end of the article. To accurately assess air leakage from a building, an air pressure test can be commissioned and in larger projects this is often done pre- and post-refurbishment Figure 1. Typical air and moisture movement throughout a traditional building. Figure 2. An infra-red image of a HES pilot building, showing the cold areas at the edge of the timber floor where there is air ingress.