As previously mentioned, the UK Levelling Up Secretary, Michael Gove, has relaxed planning rules in an attempt to densify housing in city centres, creating more “walkable, liveable communities”. However, density is a debated topic within planning. Green Alliance recently addressed this debate during their ‘Conservation vs densification: what’s next for sustainable planning?’ event.[i]
Britain has a backlog of 4.3 million homes that have never been built and put onto the national housing market.[ii] Even if the government’s target to build 300,000 homes a year is fulfilled, this housing deficit will take at least 50 years to address.[iii] Therefore, some see building more homes in the UK’s city centres as a very important way to help out Britons.
Increasing density also means more people will have greater access to public transport, which should increase its use. Centre for Cities has found that Britain’s low-rise terraced and semi-detached housing prevents more people from living near city centres and having access to public transport.[iv] This contributes to UK cities (outside of London) comparing poorly to other European cities in terms of public transport. In big European cities, about 67% of people can reach their city centre by public transport within 30 minutes. In Manchester, Birmingham, Leeds, Sheffield, Bristol, Newcastle, Nottingham, Liverpool, and Glasgow, only 40% of people can reach their city centre by public transport within 30 minutes. Centre for Cities has calculated that £23.1 billion ($29.5bn USD) per year is lost from the job opportunities and productivity that are limited by poor transport links in the UK.[v]
Density also has a relationship to surface urban heat islands (SUHIs). The urban heat island (UHI) effect is the phenomenon that cities are warmer than rural areas due to the thermal mass of building materials like concrete that absorb and then release large amounts of heat and the smaller quantity of trees and bodies of water. There are two kinds of UHIs, SUHIs and atmospheric UHIs. The sky view factor (SVF) is the fraction of the sky visible when looking from the ground up. Low-rise detached housing tends to have a higher SVF than high-rise apartments. Low-rise housing also tends to have a higher land surface temperature (LST) because the ground receives more direct solar radiation, contributing to a greater SUHI effect[vi]. However, there is a tipping point. Extremely high-rise, high-density apartments that create an SVF of less than 0.2 contribute to an increased LST because there is less green infrastructure for cooling, lower ventilation performance, higher anthropogenic heat, and decreased longwave radiation.[vii]
Whilst higher density is often associated with taller buildings, it is possible to increase density without building high-rise apartments. This is beneficial because taller urban environments have higher life cycle greenhouse gas emissions despite lower operational energy use, but low-density urban environments use more land, so having denser buildings that are not as tall addresses both problems.[viii]
Figure 1: Illustration of different urban typologies. a) High-density, high-rise, b) low-density, high-rise, c) high-density, low-rise, d) low-density, low-rise.
Figure 2: Graph of empty homes in England
Professor John Barrett from Leeds University was arguing the case for conservation at the Green Alliance event. He explained that the UK’s immediate priority needs to be reducing greenhouse emissions. Of course, there is a housing shortage in the UK, but demolishing existing building stock to create denser housing is not the solution. Demolishing and building new homes increases the embodied carbon in cities. There are currently 676,452 empty homes in England[ix] and nearly 250,000 long-term empty homes in the UK[x]. In London alone, there were 89,508 empty homes in 2022 and 34,327 long-term empty homes.[xi] Filling these homes with permanent residents would slightly ease some of the UK’s housing demand. Professor Barrett said that all options need to be explored before demolition, and this includes focusing on the needs of communities before investors. This would require some reforms of the UK’s planning system.
Gemma recently graduated with a degree in International Development. She is currently studying for an MSc in Sustainable Urbanism, which examines urban planning and urban design through a sustainability lens. “I’m passionate about addressing sustainability challenges in a holistic and pragmatic way. Zero Carbon Academy's diverse range of services targets many of the areas that need support if we are to transition to a liveable future. I’m excited to see the impact that the Academy makes.”