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Building Products March 2018

INSULATION AND ACOUSTICS INTELLIGENT INSULATION With poor airtightness reportedly responsible for up to 40% of heat loss from a building, Sarah Buchanan, product manager at Isover, explores how airtightness and moisture management can be controlled with a smart membrane. the design stage of a building. Airtightness is achieved by designing and installing a continuous air barrier around the heated volume of the building. This air barrier will normally be on the warm side of the insulation. Junctions between different materials in the air barrier should be well sealed and penetrations should be minimised and thoroughly sealed where they cannot be avoided. The airtightness level of a building is measured using the blower door test and poor airtightness can be diagnosed during a test using tea lights, candles or smoke pens to spot cracks and gaps in fabric, or by conducting a thermographic survey. The ventilation strategy must also be considered at the same time as airtightness levels. Too much air leakage leads to draughts, heat loss and wasted energy. However, too little air infiltration can result in inadequate ventilation and poor indoor air quality if the controlled ventilation within the building is insufficient. According to the Energy Saving Trust, the total ventilation rate for a home MARCH 2018 | BUILDING PRODUCTS 31 Airtightness is the measure of uncontrolled ventilation through gaps and cracks in the building envelope and it is vital that this uncontrolled ventilation is minimised. As well as preventing unnecessary heat loss, there are a lot of other benefits to doing so as well. Minimising gaps in the building fabric reduces the need for internal heating in cold weather and helps the heating system to maintain a consistent temperature within the building. This, in turn, reduces carbon emissions and heating bills for occupants. However, it is important to note that, as airtightness increases, the need for controlled ventilation to maintain occupant comfort also grows. Energy efficiency targets for new dwellings are a key element of the Building Regulations, which provide an airtightness value for a guideline ‘notional building’ as well as an absolute limit. In the UK, its values are expressed as air permeability in the unit m3/h.m2 at 50Pa (q50). This value refers to the volume of air in m3 that can flow per hour through each square metre of the building envelope at a pressure differential of 50 pascals. However, the PassivHaus standard uses a slightly different measure: air changes per hour in the unit h-1, at 50Pa (known as n50). This refers to the number of times the volume of air in the building is changed each hour at a pressure differential of 50 pascals. Reduce the risk By minimising uncontrolled ventilation, an airtight structure will also reduce the risk of condensation within the building fabric, by limiting moisture transport into the structure via convection. Indeed, this will improve the longevity of the building. What’s more, a building with high levels of uncontrolled ventilation (such as poor levels of airtightness) will also leave occupants more exposed to outdoor contaminants such as volatile organic compounds (VOCs), nitrogen dioxide and carbon monoxide, which, in turn, can negatively affect the health and well-being of the end users. As such, it is recommended that airtightness levels and ventilation are carefully considered at Continued on page 32 >>>


Building Products March 2018
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