Light and healthy homes

Findings from a new study reveal how the choice of external wall insulation can significantly impact the thermal performance and natural lighting of a room. Kingspan Insulation reports


he drive towards a healthier built environment has picked up pace in 2018 with the WELL Institute introducing the pilot WELL Standard v2. BREEAM New Construction has also been updated, with a number

of changes designed to better assess how a building will impact occupant wellbeing. When creating healthier homes, the key considerations include ensuring good levels of natural light and maintaining comfortable temperatures throughout the year. A new study has now shown that the choice of external wall insulation can significantly impact not only the thermal performance of the element but also the amount of natural light entering a room.

DAYLIGHTING Many of the health and wellbeing benefits associated with proper daylighting provision are highlighted within BS 8206-2: 2008 (Lighting for buildings. Code of practice for daylighting). Tey include a regulated circadian system, reduced symptoms of Seasonal Affective Disorder (SAD) and improved levels of vitamin D. Internal natural light levels are affected by many factors, including window

dimensions, room layout and even the choice of paint. Daylight designers must find a balance in natural light levels as too much can cause overheating, while too little can lead to dark spaces. One way to identify this is through the average daylight factor (ADF).

AVERAGE DAYLIGHT FACTOR Te ADF calculation estimates how much light will reach occupants throughout a building. To estimate this, a horizontal surface (working plane) is plotted at the height that work will typically be carried out. Te ADF then looks at the amount of daylight reaching each area of this plane, in comparison with its


Bedroom Living Room Kitchen


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total area. Te outside daylight levels used within the calculation is based on a standard overcast sky. Te final ADF is expressed as a percentage representing the average amount

of light (illuminance) on the working plane compared with outside. Put simply, an ADF of one per cent would mean the average internal light level is one hundredth that of the outdoor (unobstructed) light level. Many building codes suggest or require a minimum ADF. For example, BS 8206-2: 2008 (Lighting for buildings. Code of practice for daylighting) recommends an ADF of at least two per cent for a whole property. Te code of practice also sets minimum ADFs for individual rooms (see table). Tese values are used to define ‘provision of good daylighting’ within

BREEAM and can contribute towards the award of two credits. As previously mentioned, there is a fine balance to achieve: large areas of

glazing can result in summer overheating or excessive heat loss in winter (as the thermal performance of the glazing layer is typically poorer than the rest of a wall or roof construction). BRE BR 209 suggests that interiors with ADFs of over six per cent are likely to suffer from these issues. To ensure good daylighting provision, ADFs should therefore be in the range of around two-five per cent. | HMM September 2018 | 41

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