The built environment can affect how we sleep. Dr Darryl O’Brien identifies environmental influences and suggests some intelligent design strategies that can improve the sleeping environment.

The average person spends around one third of their lives sleeping. While most sleep scientists do not know precisely why we need to sleep, it is generally agreed that it is necessary and that the optimal sleep environment is cool, dark and quiet. This can be directly affected by thermal comfort and noise – factors that can be directly influenced by the building design.

To go to sleep, the body’s core temperature needs to decrease by about 2ºC and stabilise at this temperature. Research suggests that a temperature range of 19-24ºC is considered optimal to get to sleep and continue sleeping.

Above this range, thermal stress causes wakefulness leading to overall decreased sleep time and quality. While lower temperatures are also shown to affect sleep quality, this is in reality less of an issue as blankets and bedclothes can be used to self-regulate thermal comfort.

The next commonly known factor to affect sleep is noise. Indeed, such was the impact on sleep quality that Ancient Romans banned chariots from city streets. During Medieval times, straw was scattered on roads to muffle noise.

Noise can affect your sleep by: increasing the time it takes to fall asleep; reducing sleep depth and duration; and, leading to unwanted awakenings. Health impacts from disrupted sleep can be quite severe and include increased fatigue, heart disease, depression and reduced performance.

Studies have identified a peak noise level of between 45 and 55 decibels (dB) as capable of disturbing sleep with the World Health Organisation’s (WHO’s) 2009 guidelines suggesting an average night time exposure of 40dB measured over an eight hour nocturnal period.

The softest noise detectible by the human ear is approximately 3dB, typical speech levels are approximately 65dB and permanent hearing damage occurs at approximately 125dB. Interestingly, studies have shown that a constant background noise (white noise) is less damaging to sleep quality than sudden noises, such as slamming doors (pink noise).

The final link in the sleep chain is light, specifically natural light. We need daily exposure to daylight (within the 480nm blue wavelength spectrum) to reset our sleep clock. So while unwanted exposure to light during the night (such as street lights) can disturb sleep, missing sunlight exposure can potentially aff ect the general sleep cycle. This point has particular relevance to office workers who travel to and from work in the dark (particularly in winter) and spend their days under artificial lights (predominantly of the red wavelength). This effect can be further exacerbated by the use of some energy-efficient glasses that may actually filter out 480nm blue wavelength light.

One emerging area of concern is the question of air quality in bedrooms. The provision of natural ventilation in habitable rooms is necessary to enhance occupant comfort and health; however, reliance on natural ventilation by opening windows or doors means that the noise and thermal insulation benefits provided by these elements would be lost if used as intended. This means that increasingly, people are relying on air conditioners to maintain thermal comfort. Where no fresh air is provided in confined spaces such as bedrooms, it is possible for CO2 concentrations to rise to rates of 1,600ppm, as compared with CO2 levels of between 550–600ppm where natural ventilation was provided. Elevated CO2 levels have the potential to contribute to health conditions such as headaches, nausea, dizziness and fatigue.

THE CODE RESPONSE
A review of the relevant parts of the BCA shows that there are no obvious measures related to optimised sleep hygiene design.

In relation to sound transmission, the BCA requires a maximum sound insulation value of 50dB between housing units; however, there are no requirements for façade noise management which is a major source of nocturnal noise pollution. In relation to thermal comfort, the BCA has minimum energy efficiency requirements, but these do not extend to address the thermal comfort needs of occupants. A similar situation exists for natural light and ventilation whereby minimum floor area to opening ratios are prescribed, but these do not reflect the needs for quality sleep.

BEST PRACTICE VERSES MINIMUM STANDARDS
While the BCA may lack minimum standards in relation to the sleep hygiene environment, it is possible to identify and implement best practice design.

NOISE
Although the BCA requires minimum sound insulation between common walls, exterior walls, doors and windows, acoustic leakage can still occur that can disturb sleep. To minimise this noise pollution, door seals, acoustically-rated (such as double glazed) windows and external walls that have bulk sound insulation materials can be used. If sound insulation of around 50dB is specified for these elements, the average interior noise levels will remain around 40dB and sleep quality should not be seriously affected.

TEMPERATURE
Depending on the local climate it may be necessary to use air conditioners to maintain thermal comfort; however, fans and breeze paths can also provide effective cooling benefits. It should be noted that elements used to provide acoustic insulation (such as double glazing) are also effective in creating a comfortable thermal environment, so numerous benefits can be created from intelligent and holistic design.

LIGHT
Natural light is a trigger for wakefulness while dark is the ideal sleep environment. Controlling unwanted light in the bedroom is perhaps the easiest to self-manage, with heavy curtains (with pelmets) being effective in blocking light. It is also worth noting that heavy curtains can also provide useful sound and thermal insulation, so again intelligent design can provide a number of additional benefits.

AIR QUALITY
While an air quality meter is necessary to measure internal CO2 levels, air exchanges through door and window gaps will ensure healthy air quality. Where air quality may become an issue is when gaps must be sealed to restrict noise pollution (such as a house is on a busy road). If this is the case, it is important that the air conditioning system provides fresh air and does not simply continue to recycle the indoor air.