Can Strategic Design & Planning Help Combat the UHI Effect?

Temperature variations within buildings are to be expected. However, with the effects of climate change becoming more and more obvious, concerns are being voiced that extreme temperatures could result in increased usage of heating and cooling systems. This would significantly raise the operational carbon emissions emitted across the built environment – at a time when we need to be doing everything we can to reduce GHG emissions to achieve net zero by 2050.

It’s easy to think of ‘extreme conditions’ as being something to worry about in the future. This is especially true here in the UK, where the average maximum temperature between 1991-2020 came in at 12.79 degrees Celsius, and the average minimum temperature at 5.53 degrees. However, climate change isn’t the future; it’s the present. And we’re already starting to see real warning signs, with the Urban Heat Island (UHI) effect recently being witnessed across a number of major UK cities.

What is the UHI effect?

The Urban Heat Island effect occurs when a built-up area exhibits notably higher temperatures than the rural areas surrounding it. While the proximity of the two locations should mean that both experience similar temperatures, urban heat islands are unnaturally warm in comparison to their less densely built counterparts. And UK cities are already on track to become dangerous heat islands.

London is a prime example. Temperature records in the capital show that the city is regularly 10 degrees warmer than the suburbs. And it’s not the only city where there’s trouble brewing. It’s estimated that by 2080, London, Manchester, and Edinburgh could all be recording temperatures that are 7 degrees greater than the UK’s more rural areas – consistently, throughout the year.

Of course, on the surface this may sound like a welcome change to our notoriously chilly country. But the truth is that urban heat islands can cause devastating effects in a whole host of different ways.

Firstly, UHIs pose a significant risk to human health. In fact, even temperatures between 16 and 20 degrees Celsius can have a negative effect. A 42% rise in excess deaths was recorded in London during the 2003 heatwave. Worryingly, it’s estimated that 7000 people per year could succumb to heat by 2050; up from between 2000-5000 heat-related deaths in 2015.

Secondly, increasing temperatures mean increasing use of cooling technologies. Reports show that heating and cooling devices – including mechanical ventilation systems, air conditioners, and electric heaters – account for 35% of total energy consumption in the average building. That’s much more than the 18% of energy used to power appliances, and the 11% of energy used for interior lighting.

Why do we have heat islands?

So what’s causing the UHI effect? Well, there’s really no one single factor contributing to the creation of heat islands. In fact, naturally occurring variations in the climate can play a role. These variations have been taking place for billions of years, due to factors such as volcanic eruptions and changes to the sun’s intensity. However, ‘play a role’ is the operative phrase. Natural changes alone aren’t enough to create an effect of this extent. Anthropogenic causes are the biggest contributors.

The United States Environmental Protection Agency identifies a number of causes related to human activity. And essentially, every one of these reasons can be boiled down into two simple categories:

Increasing urban development
Loss of natural landscapes

Urban heat islands are ultimately created by a combination of the ever-expanding built environment and dwindling natural greenery. This makes architects perfectly positioned to generate solutions.

Combatting the UHI effect is a responsibility that’s falling on architects’ shoulders. Methods include utilising materials that minimise the impact of urban development, and incorporating structural features that help to maintain comfortable temperatures. It’s a responsibility they must take seriously.

Tackling the UHI effect through design & planning

It’s clear that thermal analysis must be considered during the initial design and planning phases. UHI-combatting features need to be built into the very foundations of any new building.

Early-stage thermal analysis is becoming increasingly vital. This enables architects to fully understand and consider the thermal impacts of the materials, designs, and processes they intend to utilise. Using thermal analysis data, architects can better shape their new buildings. They can incorporate materials and features that will facilitate more natural heating and cooling to combat the urban heat island effect.

Thermal analysis may include considerations such as:

Heat gain intensity
Regular building occupancy
Maximum building occupancy
Building orientation
Interior layout
Shading
Ventilation

So what does this mean for architects? It means finding innovative ways to achieve two things simultaneously: low impact heating of buildings in winter, and natural cooling during the summer.

Today’s architects are using two methods to do just that:

Building structures that better regulate temperature

A widespread shift to timber construction is being seen across many parts of the world today in an effort to eradicate the Urban Heat Island effect. Timber has lower thermal conductivity than traditional building materials such as brick, concrete, and steel. It’s therefore better equipped to keep heat locked in on cooler days, and reduce external heat penetration during the hotter months of the year. In fact, it’s estimated that wood is 400 times better at maintaining safe, comfortable temperatures than steel. Timber is an effective way to minimise use of GHG-emitting heating and cooling systems.

Incorporating urban greening practices

Evaporative cooling is emerging as one of the most critical considerations for architects. Using urban greening practices, architects can add additional insulation to their structures. These include creating green rooftops by adding planters to otherwise unused space, or supporting new tree growth around the building. Research shows that green roofs can result in around a 2.8 degree Celsius reduction in city-wide temperatures, helping to ease the UHI effect. Additionally, the evaporation cooling properties of green roofs can lower the total energy usage of the building by around 0.7%.

Our future lies in green, sustainable infrastructure

The Urban Heat Island effect is a significant concern. It’s true that densely packed cities may always record slightly higher temperatures than their rural surroundings. However, the extent of the variation that we’re on track to observe could have devastating implications on both human health and our country’s carbon-neutral goals. Changes can certainly be made to existing structures to help counteract the UHI effect, but our main priority must be centred on reducing new build impacts.

Architects are instrumental in this. And through strategic design and planning that helps to better regulate temperature through natural means, urban heat islands could become a thing of the past.