BUILDING PHYSICS 28 Reasons why rapid air exchanges are incorrectly omitted in the summer: • assumption that ventilation at night is not required in passive houses • risk of falls in children’s rooms (max. tilting of the windows) • reduced ventilation effect because of insect screens • pets (windows are tilted at most) • ground floor apartments (for security reasons, windows are tilted at most) • restriction of the ventilation effect for the apartment because of closed interior doors • noise in the surroundings especially at night In the summer, the daily fluctuations of the outdoor temperature are generally greater than in the winter. Moreover, there is a very high temperature difference on the component surfaces in consequence of the irradiation of the sun. Measures for optimisation: • increasing the heat insulation. • Insulating layers placed on the outside and masses with the capacity of storage have favourable effects on indoor temperatures. • Choice of windows: according to more recent building physical research, the heat permeability of windows has a much greater effect on the interior room temperature than the capacity of the interior masses to store heat. • The kind of the chosen insulating material does not have such decisive importance. Instead, the thickness of the provided insulating layer, as well as the material type and thickness of the cladding facing the interior room are in the foreground of the examinations. • Correct user behaviour: the room climate can be additionally improved by ventilation during the night and keeping windows and doors closed during the day. The results of the scientific studies show that the summer heat insulation can be equated only to limited extent with the components’ storage capacity. With a rising level of heat insulation, the summer temperatures in the room fall to a comfortable measure. CLT BBS elements have a positive effect in this because CLT BBS provides simultaneously good insulation from heat as well as excellent storage capacity. The simulation of a single-family home shows that with increasing heat insulation, temperature exceedances become much less frequent and are by far weaker. The experiences gathered by residents, too, show that comfort and room climate in timber houses are consistently evaluated as being positive also during the summer. Humidity regulation Wood as a natural and replenishable raw material has many positive building physical properties. One is the ability to absorb moisture and release it again. Thus, CLT BBS has a reducing effect on the peak values of humidity in rooms (see Figure 15). At a room temperature of 20 °C and relative humidity of 55 %, 1 m³ CLT BBS stores around 43 litres of water. If the relative humidity changes from 55 % to 65 %, 1 m³ CLT BBS absorbs a rounded 7 litres of water from the room air. Figure 15 – Absorption behaviour of different building materials ABSORPTION PROPERTIES CLT BBS Concrete mortar Humidity (%) 0 20 40 60 80 100 Concrete Brick 35 30 25 20 15 10 5 0 Mass-specific water content (%) -65 -12
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