Climate change is laying bare the inability of ageing, inefficient housing stock to keep occupants cool during hot weather. With another sweltering summer on the cards, Tim Clark explores what can be done to address the UK’s overheating homes problem
Once a month, the UK’s Met Office publishes its long-term forecast for the UK. In the midst of data and computer models looking whether it will be rainy, dry, windy or a washout in last week’s update, one thing stood out.
The forecaster predicts that the UK’s climate this summer, whatever the day-to-day weather, will be hotter than the average 30-year trend from 1990 to 2020.
When it comes to the UK’s built environment, the hotter summers pose a problem in particular for homes, which have not been designed to handle sustained hot spells.
Rob Harris, senior principal at Introba, says that the issue is a historical aspect of the UK’s homes, which were arguably built for a colder climate.
“Many of us will remember just how uncomfortable the heatwave was last year and the challenge of keeping homes cool.
“Properties just haven’t traditionally been designed to cope with these extremes but increasingly landlords, contractors and supply chain teams are going to have to anticipate changing weather patterns and the demands they put on housing.”
The impacts of a hotter climate is already being felt. On 19 July last year, a record temperature of 40.3 °C (104.5 °F) was recorded and verified by the Met Office in Coningsby, England.
During the same heatwave in Dartford, south-east London, parts of the local road network were affected by scrub fires.
A number of homes in the village of Wennington, situated north of the Thames east of Dagenham, burnt down during the heatwave, prompting concerns that UK homes aren’t built to withstand the fire aspect of hot summers.
“Serious overheating has already become more frequent and more severe in England, and is projected to increase as our climate changes,” says Philip Box, policy advisor at the UK Green Building Council (UKGBC).
“One in five homes experience overheating, even during relatively cool summers, and by 2050, overheating could cost more than £1bn every year in energy, while heat-related deaths could increase by 250% compared to today.”
In total, the UK’s Climate Change Committee (CCC) – a body setup to monitor and assess the impact of climate change on the UK – estimates that adaptation to the full range of climate threats could cost up to 4% of UK GDP by 2050, which is nearly twice the cost of the armed forces and more than the entire current UK budget deficit.
Seeking shade
According to UKGBC’s Box, most of the technology and design solutions for overheating homes already exist, and are relatively simple.
“First, we can limit the solar gains through external shading, improving energy efficiency, using reflective paints, or utilising nature-led solutions like tree shading, neighbourhood greenspace, or green roofs,” he says.
“Mechanical cooling solutions like air conditioning or air-to-air heat pumps are also available, though these should generally be used as a last resort to reduce energy demand.”
The carbon-cost of cooling homes is also an issue which Introba’s Harris is keen to tackle. He agrees that placing air conditioning in buildings may seem like the simple solution, but it doesn’t solve the main problem of overheating homes and can add to the energy burden of the UK electricity grid.
“Crucially, we need to focus on design solutions which don’t call for large amounts of mechanical cooling,” Harris warns. “Homes full of air-conditioning systems to mitigate failings in the building’s passive design, ultimately adding complexity to projects and cost to developers and residents alike, will only set us back in the battle against carbon and climate change.”
Hotting up
Local authorities and town planners could also work to help bring down rising temperatures in UK towns and cities. Urban centres act as heat islands, raising local temperatures by a few degrees compared with the rural areas that surround them. In London, the difference can be as much as two to three degrees higher than the Homes Counties.
A number of studies, including a recently published report by Pennsylvania State University in the US, found trees reduced surface temperature and median radiant temperatures, increased evapotranspiration, and provided shading.
The study also found that increasing the height compared to the width of building was beneficial, stating: “It is recommended that the utilisation of taller and denser buildings with higher albedo pavement surfaces should be considered to enhance thermal comfort conditions, particularly in urban blocks with limited vegetation coverage.”
Narrower streets can also help mitigate overheating effects. While this may do little for the UK’s swathes of detached cul-de-sacs and estates, it can help influence UK urban design.
“Homes full of air-conditioning systems to mitigate failings in the building’s passive design will only set us back in the battle against carbon and climate change”
Rob Harris, Introba
When it comes to our existing building stock, Ste Garlick, senior architect at global multidisciplinary design practice BDP, says that the importance of fabric-first energy efficiency measures in decarbonising our existing cannot be overstated, and improvements to insulation and the thermal performance of doors and windows can help minimise overheating when undertaken carefully and via a holistic ‘whole house’ approach.
“This must consider how retrofit measures work together, and will likely incorporate airtightness works, ventilation upgrades, and various steps to mitigate overheating risks,” he says.
“Retrofit projects must start with a careful assessment of overheating risks using tools such as that developed by the Good Homes Alliance, and using weather information that accounts for climate change to improve resilience to rising temperatures and heatwaves. Passive measures should also be prioritised to avoid the need for active cooling and the associated carbon emissions.
“Whilst existing buildings are often subject to inherent overheating risks presented by site, location, and orientation, retrofit provides a unique opportunity to address some of these issues.
“For instance, insulation works often involve the repositioning of windows to mitigate thermal bridging, and therefore the opportunity to establish deeper reveals to improve shading. Physical shading elements may also be installed, or insulated pattresses incorporated within insulation to accommodate future installation.”
The UKGBC has a number of tools available to help designers, planners, and architects brush up on the latest innovations in home design. These include 3D models for microclimate to apply different design iterations to, examples of more efficient heat transfer fluid in buildings, as well as case studies of the impacts of green roofs and climate risk models linked to overheating.
Cooling down
According to T&T’s McWilliams, an initiative led by the mayor of London’s innovation partnership encourages a “whole-house” retrofit approach that focuses on delivering guaranteed improvements in overall energy performance – through winter and summer.
“At the core of such an effective retrofit approach is the government-supported standard, PAS2035, that includes design criteria for both extremes of temperature,” he says. “This is part of a design and construction methodology that will verifiably deliver the intended occupant level of comfort.
“This may mean combining insulation improvements with some form of mechanical ventilation – and connecting the home heat pumps or heat networks that provide sources of both heating and cooling.”
The biggest obstacle to installing measures to limit heat exposure remains funding.
“The scale of the retrofit challenge in the UK is immense, but we have two large, related issues: insufficient funding and an acute skills gap,” Garlick says.
For landlords and homeowners a number of funding streams exist, such as the Energy Company Obligation 4 (ECO4), which is designed to tackle fuel poverty and help reduce carbon emissions by placing an obligation on energy companies to deliver energy-efficiency measures to domestic premises.
The government’s Home Upgrade Grant (HUG) provides energy-efficiency upgrades and low carbon heating via local authority funding, to households in England that are low income, off the gas grid, and have an Energy Performance Certificate (EPC) between D and G. Up to £630m of grant funding is available for successful local authorities to help them deliver HUG 2 from April 2023 until March 2025.
Compared to the multi-billion-pound bill parliament has estimated it will take to upgrade the UK’s homes to more energy efficient status, the £630m isn’t much. But it is a start.
A further fund is the Social Housing Decarbonisation Fund (SHDF) which can help reduce the cost of retrofit works. T&T’s McWilliams says that for commercial landlords which may not qualify for such schemes there are green loan finance options, and possibly the emergency of energy companies starting to offer self-financed approaches.
A further fund is the Social Housing Decarbonisation Fund (SHDF), which can help reduce the cost of retrofit works.
“Whilst there are encouraging signs on funding, such as the Social Housing Decarbonisation Fund (SHDF) contributing towards large-scale retrofit projects, progress is far behind what is urgently needed as climate change risks continue to grow,” Garlick adds.
“Despite this, whilst the SHDF demonstrator projects targeted relatively ambitious levels of energy efficiency and occupant comfort, subsequent SHDF waves have decreased in scope and budget.”
With storms brewing over the UK, the season of balmy days and nights gives the UK’s architects, developers, and urban planners plenty to mull over when it comes to alleviating overheating in UK homes.
Harris adds: “We need to embrace different materials and systems as an industry that solve this issue resiliently, passively, and most importantly, simply.”
Main image: Juergen Faelchle/Shutterstock
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