Sleep Well - Designing a Good Night's Sleep in a Warming Climate

By Henry Pelly

05 April 2018

You’re awake. Again. Still. The covers are off and your skin prickles with moisture. The low, glowing light of the clock says 5.05. The heat cloys at you unrelentingly. You’ve tried everything but there is no relief…

Sleep is a fundamental human need. But over the past 150 years, industrialised society has undermined the amount and quality of sleep we get. The evidence that our lack of sleep is having a negative impact on our health is mounting. Almost every major disease in the developed world - Alzheimer’s, cancer, obesity, diabetes – shows a causal link to our lack of sleep.

The design of our cities and bedrooms has a big impact on the quality of our sleep. In order to fall asleep, our core temperature must drop by 2 degrees. We need environments that are dark, quiet and cool. Bedrooms that are too hot prevent this happening. Many people living in cities have to make a difficult choice between a bedroom which is too noisy and a bedroom which is too hot. In developments in cities across the UK, bedrooms are not being designed to be cool, dark and quiet. This means many people are becoming sleep deprived because their bedrooms are not designed to meet our sleeping needs. The simplistic response is to install comfort cooling but this is energy intensive, expensive to operate and costly to the environment.

The warming climate provides an additional challenge. Flats and houses built in the UK today need to support summer nights which could regularly exceed 30°C by 2080. In addition to the challenge of a warmer external environment, we are creating homes which are much more efficient at holding on to heat. New homes in the UK are being designed to minimise energy use, which means that they are better insulated, more air-tight and often serviced by centralised heating and hot water networks. This has led to an epidemic of new homes that are unable to lose excess heat and are overheating during the hotter months.

It’s possible to design bedrooms that deliver both optimal sleeping environments and minimal environmental impact. Sleep has always dictated residential architectural design. Whether it’s the indoor, open fire or the four-poster bed, the importance of good sleep has been understood and catered for in design for centuries. There are many factors that aid a restful sleep. The renowned sleep researcher Professor Matthew Walker describes thermal environment as the most under-appreciated condition determining the ease with which we fall asleep.

So, what is overheating?
The NHBC’s overheating guide¹ provides an excellent description

“most people begin to feel ‘warm’ at 25ºC and ‘hot’ at 28ºC... 35ºC is the internal temperature above which there is a significant danger of heat stress. However, overheating is not just a function of high temperature, other factors such as lack of air movement and sustained exposure to high temperatures will also affect the comfort level of occupants. Furthermore, some factors may only manifest themselves in particular geographical areas or at a ‘micro-scale’, such as the ‘heat island’ effect, which is particular to dense urban areas.”

The Problem
The National House Building Council (NHBC) produced an excellent review² of overheating in homes at the end of 2012, saying: “overheating ranks amongst our greatest concerns that need to be addressed as a priority.”

The NHBC review highlights three particular groups at risk:

  • “The elderly are at an increased risk from heat-related illness”; “in those above 75 years old sweating is reduced or possibly absent”.
  • Obese individuals “generate more heat during activity”, “require less heat to be produced before their core temperature begins to rise” and “a strain is put on the cardiovascular system of obese individuals who already have a decreased cardiac output.”
  • “Urban dwellers are at an increased risk of heat illness due to the UHI [Urban Heat Island] effect. In London during the 2003 heatwave, temperature differences between London and the surrounding rural areas at times exceeded 9°C.”

An ageing population, increasing obesity and swelling cities, combined with noisier and dirtier air and hotter temperatures from climate change sets the stage for a fairly serious problem. The review cites the 2003 heatwave in northern France that “resulted in 15,000 excess deaths”, and states that “2,000 deaths in the UK per year” are caused by “excess heat”.

Causes of Overheating
The NHBC review states:

“Historically in the UK the use of heavyweight construction materials and limited amounts of insulation, allied with high levels of infiltration through gaps in the building fabric, have contributed to minimise overheating.”

“There is increasing evidence that new and refurbished properties are at risk of overheating, especially small dwellings and flats and predominantly single sided properties where cross ventilation is not possible.” They highlight “lightweight, airtight houses with little or no solar shading”, “often designed with large areas of glazing, mechanical ventilation and/or communal heating systems”, that “have the potential to overheat throughout the year, not just in the summer months”.

Add to this inefficient heating pipes, massive flat screen televisions, high density occupation for social housing, and it all means our bedrooms are at risk of becoming uncomfortably hot for most of the year.

Our Proposed Design Solutions
Some of the short-comings in the design of bedrooms include excess solar gain, window openings that are undersized for a heavyweight room, and the inability to open the windows due to excess noise and air pollution. All these factors and more can detrimentally impact on a good night’s sleep.

An alternative design could mitigate some of the factors that intrude on sleep. This includes a smaller area of glazing; one that still affords daylight and views but reduces solar gain and overheating. It includes an acoustically attenuated ventilation grille; one that still allows for some external air to enter the room but reduces the impact of external noise, particularly pertinent in cities. This alternative design also includes the installation of a ceiling fan – a seemingly simple way to aid a restful night’s sleep, installed in warmer climes all over the world but one rarely employed in the UK. It will become increasingly necessary here.

Our design fundamentals aim to focus on the following principles, which if properly integrated into a scheme will help mitigate overheating:

  • Provide all accommodation with cross ventilation.
  • Reduce solar heat gains entering the building by using appropriate window areas, shading devices and solar control glazing.
  • Design large openable areas in the façade to purge the home of heat.
  • Design secure ventilation which will be used to ventilate in summer when the occupant is out or sleeping.
  • If a communal heating system is used, ensure enhanced levels of pipework insulation, keep pipe runs as short as possible and design the system to work on low operating temperatures. This can be achieved through multiple, smaller rises with smaller pumps to reduce the overall auxiliary load.
  • We might even consider providing a mesh layer in the bedroom walls, which would effectively block electromagnetic radiation, known as a "faraday shield". This would enforce a digital blackout in the bedroom.

Current vs. Optimal Bedroom Design

In Summary
Sleep is a fundamental requirement for good mental health. But a combination of factors are conspiring to rob us of a good night’s sleep - most acutely is that of overheating bedrooms. Climate change is nudging up external temperatures, the increasing densification of cities leads to the urban heat island effect, and ever worsening air pollution and external noise prevents us from opening the windows. This is all leading to an epidemic of thermal insomnia. Worse still, overheated homes have been directly linked to premature deaths in the elderly. Something needs to be done.

We want to stimulate people to think about their own houses and their own bedrooms, and to contribute to the debate about the nature of good design in the UK. It's important to get people to consider the wider implications of climate change on their lives and the lives of generations to come.

We encourage people to share their experiences, both good and bad, in the comments section of this blog.

¹ Understanding Overheating – where to start: An introduction for house builders and designers, NHBC Foundation, July 2012

² Overheating in new homes: A review of the evidence, NHBC Foundation, November 2012



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