Heritage Retrofit

10 BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION THE EASY WINS A strategic approach to improving energy efficiency in traditional homes RACHEL COXCOON T HE PAST three years have seen an explosion in retrofit activity, not least because of the heavily promoted (but now defunct) Green Deal programme. External wall insulation in particular has been promoted heavily by government as the number of unfilled cavities and lofts has diminished and policymakers’ attention has turned to the ‘hard to treat’ sector, which includes almost all buildings of traditional construction. 1 However, the list of approved measures under the Green Deal did not include some of the simplest available interventions. An unfortunate side-effect of this omission has been to focus public awareness on the more expensive, disruptive and (for traditional buildings) potentially damaging 2 measures at the expense of easier, cheaper and less disruptive ones. Growth in demand for these more expensive measures has also created opportunities for less skilled operatives to move into this area of work. This has increased the risk of poorly applied external wall insulation systems being carried out by general building firms without the specialist knowledge needed to specify each system to the bespoke needs of the house in question. This is especially true of traditional buildings, which function differently to modern ones, particularly with regard to how air and moisture move around them. Modern buildings rely on a high level of air and moisture tightness, and the design aim is to create a sealed envelope that keeps most moisture out through the use of moisture-resistant materials and finishes. Excess moisture such as that generated in bathrooms and kitchens is typically expelled mechanically via extraction fans or, at the very least, trickle ventilation in windows. Applying an external render that adds to the already impermeable design can significantly improve some more modern buildings in terms of thermal performance. By contrast, traditional homes (partly because they pre-date the technical ability to achieve moisture tightness) have tended to work with flows of moisture. Damp from the ground, driving rain and occupant use would have travelled through the walls and occupants principally relied on sunshine, wind, heating and ventilation through windows, chimneys and draughts in order to keep the building at an acceptable equilibrium. Since many traditional homes were not originally constructed with an internal bathroom, plumbing or central heating, and because the idea of taking a daily bath or shower would have seemed like madness to many of our predecessors, the amount of moisture generated daily by a household would have been much lower. Most traditional homes now have these features, so the fabric of those buildings must deal with far higher levels of moisture than in the past. When coupled with the application of impermeable insulation materials and insufficient ventilation, this can have disastrous consequences. Moisture that would previously have travelled through the walls is now trapped inside. Mould and mildew can build up and eventually cause damage to the fabric. It is therefore vital that those living in traditionally constructed homes are asking potential contractors the right questions about the system that will be used and the way that excess moisture will be dealt with. Less well documented, but perhaps of equal concern, is the effect that new external finishes can have on the historic significance of many traditional buildings. The Centre for Sustainable Energy (CSE) Tightly packed Georgian housing in Bath: intrinsically sustainable design with a low ratio of external envelope to interior