The Building Conservation Directory 2022

101 C AT H E D R A L COMMU N I C AT I O N S T H E B U I L D I N G CON S E R VAT I ON D I R E C TO R Y 2 0 2 2 METAL , WOOD & GLASS 3.3 using what is called a ‘door blower test’. The results are given in ‘air changes per hour’(ACH) at a standard pressure and prescribed conditions. Many older buildings will have test results in the region of 15 ACH; modern standards are much lower than this. In a recent HES pilot with windows and flues excluded, a measure of eight ACH was achieved. To better understand discomfort and why some rooms may never get up to a reasonable temperature, it is also helpful to understand where the main areas of air movement are. For this an infra-red survey is useful. Many companies offer this service, sometimes with drones to get a close look at high level areas. Depending on the calibration, warm air moving out through gaps will generally show as red areas, and cool air coming in will show as blue or cold areas. This is often seen around skirting boards and where there are gaps in linings. Infra-red images will also show conduction losses where there is heat moving through the fabric. In some projects the IR survey is done at the same time as an air building air pressure test. Figure 2 shows a typical image showing cold spots due to cooler incoming air around the edge of a suspended timber floor. Draughts and heat loss by excessive air movement in traditional buildings should be addressed using technically appropriate methods. More detail on this and a whole house approach to energy retrofit can be referred to in the new HES Guide to Energy Retrofit of Traditional Buildings , which considers all aspects of traditional building retrofit in more detail (see Recommended Reading). However, a short introduction, considering common areas where draughts and air ingress can be addressed are discussed below: FLOORS A cold floor can absorb heat and, in the case of suspended timber floors, can introduce cold air from below the floorboards. This can affect the perceptions of thermal comfort in a house. If you have bare floorboards with larger gaps between the floorboards, these can be filled either by using thinner strips of wood glued in or a flexible sealant for more narrow gaps. Carpets can also add to thermal comfort and reduce noise, but if installing new carpets, consider choosing a breathable underlay and carpet. Insulating timber floors will also address air infiltration; insulation can be fitted between the joists, using a vapour permeable material such as hemp and wood fibre board. Tests on HES case studies have shown such materials to be appropriate for the insulation of suspended timber floors, achieving significant thermal improvements. Vapour open materials are preferred in traditional building retrofit as they allow humidity concentrations to dissipate through the material assemblies. These principles are discussed further in the HES Guide to Energy Retrofit . WINDOWS Windows are often the first components to be addressed when thinking about draughts as they are one of the main sources of air infiltration in a home. Draughtproofing the sashes or casements can reduce air leakage by up to 80 percent. A range of products is available, from brush strips to foam cushions, or a type of cushion strip applied to various parts of the window. This can be on the casement (figure 3) or on the frame. These do range widely in cost and durability, so ask for samples and look at examples of previous work. When upgrading windows in this way, Building Control may also require the introduction of trickle vents to ensure internal conditions remain healthy. Secondary glazing is a good way to reduce air ingress. This is essentially a second window installed internally next to the original window to reduce air leakage and conduction heat losses. It is effective, reducing heat loss by around 60 percent. Figure 4 shows secondary glazing on a HES pilot cottage on South Uist in the Hebrides. This is a polycarbonate sheet, held to the window case with magnetic strips. There are many other versions of such glazing, some are fixed in place, some openable on sliders, and some are of a shutter type. The type chosen will depend on circumstances, but an important factor is choosing a product that allows the shutters, if you have them, to close effectively. For listed buildings secondary glazing does not normally require listed building consent, although owners should check with their Local Authority Planning Department. DOORS Like windows, doors can introduce cold draughts from outside or allow warm air to escape through their edges. The most common means of addressing this is by draught proofing around the door frame. There are various ways to do this, with a range of products to suit the conditions and the value of the door itself. For standard doors, brush strips set into a cut channel Figure 3. A newly fitted cushion strip on a casement window as part of the HES pilot at Holyrood Park Lodge Figure 4. An HES pilot project in the Western Isles, which includes a double-glazed unit within the wooden sash and secondary glazing – a polycarbonate sheet held in place with a pale coloured magnetic strip.