September 2022

As we all know from the heatwave we experienced in July and August, the climate is warming to unprecedented levels due to increased carbon emissions.

As the UK government’s Climate Change Risk Assessment highlights, this poses clear and substantial risks to health, life, vital services such as healthcare and education, and the economy.

The UK launched its Net Zero Strategy last year to reduce these climate-wrecking emissions and decarbonise all sectors of the economy, with a plan to achieve net zero by 2050.

With 17% of UK greenhouse gas emissions coming from buildings, mainly attributable to burning fossil fuels for heating [1], urgently addressing this is crucial in our journey to net zero.

That’s why the UK launched the Heat and Buildings Strategy last year, which sets out how we will decarbonise our homes, and our commercial, industrial, and public sector buildings with a £3.9 billion funding pot.

Buildings in this country are not designed to cope with the high temperatures we’ve had recently. Many of our homes and workplaces are already too hot in summer and too cold in winter. So, addressing this is not only vital for decarbonisation, but also for indoor thermal comfort of occupants.

Traditionally, policy has always focussed purely on energy efficiency, but the Heat and Buildings Strategy sets out a holistic approach to designing safe and comfortable buildings for the future considering energy efficiency, low carbon heat, overheating, indoor air quality and flooding risk, with new legislations in the form of Building Regulations being one method to achieve this.

In June this year, new Building Regulations came into force including the entirely new Approved Document O, set up to mitigate the risk of overheating in new homes, which the Climate Change Committee says is one of the highest priorities for an effective response to climate change in the UK.

WHAT IS OVERHEATING?

CIBSE define overheating as: ‘conditions when the comfortable internal temperature threshold of 28°C is surpassed for over 1% of the time’. It is a major concern as overheating not only causes occupant discomfort, but can also negatively impact health, wellbeing, and productivity [2].

Furthermore, CIBSE states that there is a significant danger of heat stress if the internal temperature is above 35°C. In extreme cases, this can cause fatalities. According to the Department for Levelling Up, Housing and Communities, there are about 2,000 heat-related deaths in the UK every year and if not addressed, overheating in buildings specifically is expected to cause some 4,500 premature deaths per year by 2050 [3].

WHY IS OVERHEATING OCCURRING?

Aside from the obvious increase in outdoor temperatures, there are a multitude of factors leading to the increased risk of overheating in modern buildings including:

• Modern buildings are heavily insulated to retain heat and designed to be more airtight to prevent heat loss and energy wastage, with efficient design standards such Passivhaus becoming more popular.
• Natural ventilation is either inadequate or non-existent. In some high-rise buildings windows cannot be opened so there is no natural escape for the heat and solar gains. Similarly, if a building is near airborne noise or pollution from busy roads, railways or industrial sites, occupants will be reluctant to open windows so heat will accumulate inside.
• Urban areas are hotter due to the ‘urban heat island effect’ where hard surfaces such as roads, paved areas, and rooftops absorb large amounts of solar radiation.
• Internal gains from electrical appliances, lighting, and the activities of occupants such as cooking, bathing, and showering all generate heat.

HOW CAN WE MITIGATE OVERHEATING?

The revised Building Regulations document states, ‘All new residential buildings, including homes, care homes, student accommodation and children’s homes, must be designed to reduce overheating, making sure they are fit for the future and protect the most vulnerable people.’

This can be done by designing and constructing the building to achieve both of the following:

• Limiting unwanted solar gains in summer.
• Providing an adequate means of removing excess heat from the indoor environment.

Mitigating solar gains

The obvious first step is to reduce solar gains (heating due to direct sunlight). Approved Document O broadly states that this can be achieved through:

• Fixed shading devices such as shutters and blinds.
• Glazing design, including size and orientation.
• Building design, for example, the placement of balconies.
• Shading provided by permanent adjacent buildings and structures.

Removing excess heat

Despite reducing solar gains, there is still a likelihood of overheating and may be a need to remove heat from the building. Methods for removing excess heat allowed under Part O are:

• Opening windows (effectiveness improved by cross ventilation).
• Ventilation louvres in external walls.
• A mechanical ventilation system.
• A mechanical cooling system.

The regulations state that passive means, i.e., no energy usage, should be used as far as reasonably practicable to limit solar gains and remove excess heat. But the issue with natural ventilation, i.e., opening windows, is that it can be ineffective at cooling the internal space during hot outdoor conditions, and in urban areas, can permit polluted air in while removing any sound insulation and security benefits.

In many cases, there will be a need for mechanical cooling and/or mechanical ventilation. Of course, the issue here is that, like a heating system, it uses electricity/energy to operate.

THE NEED TO MAINTAIN GOOD INDOOR AIR QUALITY

Alongside Part O, Part F of the revised building regulations highlights the need to maintain good indoor air quality (IAQ) and may present designers with challenges in terms of meeting energy usage levels, thermal comfort and good IAQ for building occupants.

The recent uplift to Part F includes a new requirement that when any improvements, extensions or renovations are done to a building, the ventilation is no worse than before the works began. The works must also comply with all regulations concerning controlled services such as cookers, boilers, fires, or electrics. 

Moreover, there is a recommendation that all replacement windows are fitted with trickle vents unless there is an alternative form of ventilation, such as whole house mechanical ventilation with heat recovery (MVHR).

MECHANICAL COOLING + VENTILATION: WHAT ARE THE OPTIONS?

If passive means of cooling are inadequate for a particular building, then mechanical cooling should be used, and mechanical ventilation may also be considered for improved IAQ.

Jaga offers a range of energy-efficient heating and comfort cooling solutions, with optional ventilation provision, suitable for connecting to any heat source, particularly heat pumps and low-temperature systems.