106 THE BUILDING CONSERVATION DIRECTORY 2025 CATHEDRAL COMMUNICATIONS DRAUGHT-PROOFING IN HISTORIC BUILDINGS TOM COLES and DAN RAYMOND BARKER EFFECTIVE DRAUGHT-PROOFING in traditionally constructed buildings requires a careful balance between retaining essential ventilation and minimising heat loss. Unlike modern buildings, which prioritise airtightness, older buildings have depended on air movement (including draughts) to prevent damp and maintain indoor air quality. Building conservation professionals must navigate these complexities to ensure energy efficiency improvements do not compromise a building’s health. Proper ventilation is crucial for maintaining indoor air quality, preventing moisture buildup and ensuring occupant comfort in all buildings, no matter when they were built. Many older structures were designed with natural airflow in mind, incorporating chimneys, timber windows and wall vents to promote circulation. As buildings have been modernised with insulation, register plates and sealed windows these passive ventilation mechanisms have often been restricted, leading to condensation, mould growth and poor air quality. Natural ventilation in older buildings typically occurs through gaps in walls (around pipes and cables), around windows and doors, through floors and skirtings, and through passive systems like stack effect, where warm air rises and escapes through upper openings while drawing in cooler air from lower levels. Understanding these airflow patterns is essential when renovating or retrofitting an older building as blocking or altering these pathways without compensating with controlled ventilation can lead to unintended consequences such as high humidity or stale, polluted air. Traditional construction materials such as lime plaster, timber beams and masonry walls rely on ‘breathability’ to manage moisture levels effectively. Breathability technically refers to the movement of air through building fabric but is used as a shorthand for water permeability or openness to the movement of water vapour. Inappropriately applied modern materials, such as cement-based renders or synthetic paints and sealants, can prevent this natural movement, trap moisture and accelerate decay. While maintaining healthy airflow (ventilation) is important, excessive draughts (infiltration) can lead to significant heat loss, discomfort and increased heating bills. The challenge for conservation specialists is determining where background infiltration is beneficial and where it should be controlled. Out of 30 million homes in the UK, six million were built before 1919. Many remain unimproved featuring little or no draught-proofing, single-glazed windows, minimal loft insulation, solid walls and uninsulated floors. ASSESSING HEAT LOSS FROM DRAUGHTS Before introducing any draught-proofing measures to a period property, it is essential to conduct a thorough assessment. Windows and doors are obvious heat loss areas but floorboards, chimneys, loft hatches and entry points for cables and pipes can also be major culprits. Other sources include gaps in skirtings, suspended floors over ventilated voids and gaps in timber-framed structures. A careful inspection should include looking for signs of previous inappropriate repairs, such as foam sealants or hard mastics, which may have cracked over time, causing further air leakage and material deterioration. Additionally, misaligned or warped wooden components can introduce gaps that must be addressed with flexible and breathable sealing techniques. Research suggests that in a typical uninsulated two-storey detached house, heat loss via draughts and infiltration may account for approximately 30 per cent of total heat loss for the whole building. In semi-detached, terraced and multi-storey buildings, this percentage can be even higher due to proportionately lower heat loss through walls and floors. Air pressure tests, thermal imaging and smoke tests can help identify problem areas – often these are used in combination. In many cases, though, an expert will be able to make an assessment from simply examining the key elements. And often the occupants know all too well where the main sources of draughts are! DRAUGHT-PROOFING SOLUTIONS Windows are often a significant source of draughts in historic buildings. Draughtstripping is a straightforward but highly effective way of reducing air leakage. Traditional solutions, such as brush seals Draught sources can include chimney flues, doors, windows, vents and miscellaneous gaps. (Photo: Jonathan Taylor)
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