The Building Conservation Directory 2023

55 C AT H E D R A L C O M M U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 3 | C E L E B R AT I N G 3 0 Y E A R S B U I L D I N G C O N T R A C T O R S 2 UPGRADING WINDOWS It has been normal practice to upgrade the performance of windows through wholesale replacement with sealed double-glazed units, or the insertion of thin sealed double- glazed panes within the existing window sashes. Either approach affects the historic fabric and appearance and may therefore also affect their significance. Secondary windows, by contrast, can be a reversible intervention, and, if double-glazed, have the effect of creating triple-glazed windows without loss of fabric and with minimal impact on appearance. On sash windows, secondary windows should always be in two parts, coinciding with the meeting rails of sashes, so that they can be opened for cleaning and maintenance. On casements the secondary window should similarly reflect the form of the original, with one or more opening lights as necessary. Steel windows can be hinged, but minimally- framed aluminium windows with sliding casements can be more discrete. In either case it is desirable to paint the outside of the stiles or rails of the secondary windows black, so that they disappear when seen from outside during the day when the windows read as dark voids. Since the secondary window installation is reversible – often carried out with magnetic tape fixing – it is possible to take a seasonal approach, reverting to the original fenestration and appearance by removing the secondary windows during the warmer months. UPGRADING INSULATION Research and testing carried out by the SPAB has shown how the thermal performance of traditional construction is often superior to that predicted by theoretical models. Nevertheless, the improvement of thermal insulation can make a considerable improvement in thermal performance as long as this is kept in balance with the impact on historic materials, character and appearance. The easiest impact can be achieved is by increasing the insulation in the roof and where there are voids that can be reached without adverse impact; always subject to avoiding problems of condensation. More difficult is the addition of wall insulation, particularly where there are elements of historic significance, such as timber lath and plaster, decorative plaster cornices, skirtings, window shutters and other trim. The significance of these elements must be assessed before deciding to add a layer of insulation to the inner face of an outside wall. One option might be to bury features behind the insulation and either accept their loss or replicate them above in a manner that is entirely reversible and retains much of the character of the interior. Another option is to physically move details of historic significance inwards and place them on top of the newly insulated wall surface. An experiment was carried out in one Victorian house, upgrading the insulation of windows, doors and walls in ways that take account of the performance of traditional, breathable fabric, rather than the highly insulated, highly sealed and highly engineered performance of new buildings. Materials were chosen that can be installed at very low cost by anyone on a DIY basis. The sash windows were draftstripped and a sheet of acrylic glazing was hung over the face of each window to provide almost invisible secondary glazing. Each is fixed by means of magnetic strips so that the panes can be easily taken down in summer. Duvets have been hung against the outside walls on brass picture hooks on the existing picture rail and decorated with sheets of fabric in muliti-colours, obtained from a market stall in Whitechapel Market. HEATING Electricity is increasingly derived from wind and solar energy, with no greenhouse gas emissions. The emphasis is now therefore on heat pumps – ground-source or air-source – that can supply around three times as much heat energy as the electricity they use. However, the water circulating from heat pumps is generally at a lower temperature and may require a greater area of radiators than conventional gas- or oil-fired heating, or may entail damage or destruction to historic floors in order to insert underfloor heating. The fallback may be an electric boiler used in conjunction with the existing pipework and radiators. Alternatively, on the analogy of open fires that would traditionally have been the only heat source, there is the possibility of radiant electric heaters used in the original fireplaces that are rapid response and need only be switched on when the room is in use, or, in rural areas, woodburning stoves placed in the original fireplaces. SOCIAL, ECONOMIC AND ENVIRONMENTAL SUSTAINABILITY The measures outlined above will help old buildings make a substantial contribution to mitigating climate change. However, this is not the only measure of sustainability for old buildings. All three pillars of social, economic and environmental sustainability apply to pre-1919 buildings generally and to listed buildings in particular. Those that are open to the public serve vital social purposes as centres of the local communities, contributing to social identity, meaning and well-being, and those privately owned also contribute fundamentally to a sense of place. Old buildings can contribute to economic sustainability through their uses, and their adaptation to accommodate present day needs is a well-known driver of the regeneration of run-down areas and towns, a vital ingredient in changing perceptions. The various funding regimes for heritage economic regeneration and heritage action zones have proved remarkably successful. The National Lottery Heritage Fund has allowed run-down listed building of high significance to resume a vital role at the heart of public life. Funding is dependent on a balance of environmental, social and economic improvements. Environmental benefits include the repair and upgrading of the historic fabric to bring out its inherent historic and architectural interest as well as to meet current requirements. Social benefits include making the buildings accessible, welcoming and able to accommodate a range of uses that benefit local residents, visitors from afar and others who use the building and its surroundings. Economic improvement and sustainability Poorly designed secondary glazing introduces an incongruous vertical element in the middle of these fine sash windows (Photo: Richard Griffiths Associates) Hanging duvets on outside walls and covering the windows with sheets of acrylic provide rudimentary insulation methods in this experimental study (Photo: Richard Griffiths Associates)