40% of global energy is consumed by buildings and is expected to increase due to expanding cities eventually to become mega cities. Building materials utilise low albedo surfaces and can absorb up to 80% solar radiation whereas high albedo surfaces deflect up to 90% of solar radiation. Such surfaces can increase the surface temperature by up to 6ºC with a mean intensity of 3.8ºC.
UHI has two characteristics, the urban canopy layer (UCL) and the Urban boundary layer (UBL) and both directly affect street canyons within the urban environment. UCL is the air between the ground and roof and is influenced by the urban surroundings, e.g., building facades, pavements and vegetation providing shelter from the wind while UBL is the layer above roofs and affected by wind.
Anthropogenic heat contributes to London’s air pollution, thus exacerbating the UHI phenonium. Pollutants produced as a result of Anthropogenic heat are Nitrogen Oxide (NO2), Sulphur dioxide (SO2), matters PM2.5 and PM10, Ozone and carbon monoxide, PM2.5 and PM10 contribute to respiratory conditions costing the NHS £3.7 billion annually. Diesel vehicles are the greatest threat to a Londoner’s health as they account for 40% Nitrogen Oxides (NOX) and PM particles. The World Health Organisation researched NOX and in 2016 and determined that Diesel exhaust fumes are carcinogenic. London Councils concluded that the UK government is contravening the EU air pollution directive and the Institute Public Policy Research (IPPR) supports London Councils conclusion.
The construction sector relies on impervious materials such as Asphalt, bricks, cement, and aggregates preventing water from percolating into the urban environment. Such aggregates also contain low albedo properties and increase urban temperatures throughout the day. Current building materials such as glass and facades do not entrap exhaust fumes particles, and toxins remain air-born at ground level due to the Urban Canopy effect. Urban designers focus more on building design than environmental design; less exterior vegetation is utilised in designs reducing overall evapotranspiration. More legislation is required to within the construction sector to ensure the external urban environment is considered at the concept design stage. Future population growth will affect housing reaffirming the requirement for implementing sustainable mechanical, electrical and public health systems through legislation.
Vertical living walls are proven to benefit the environment as they reduce noise levels, naturally cools the environment and improves external air quality. A 16cm vertical living wall complete with a 4cm gap between building facade could increase thermal insulation properties by up to 30%. Living walls contain high albedo surfaces, absorbing solar radiation during the day and releasing heat at night through evapotranspiration, providing natural cooling to the urban environment. Commercial offices within cities are designed to operate during regular business operating hours and building operation is not considered at night. The UHI increases evening temperatures, therefore increasing the internal temperature of the building. For wellbeing, commercial buildings must be cooled during the night especially during the summer nights before the morning shift.
Incorporating green roofs into architectural designs can reduce surface water run-off, therefore reducing pressure on an aging drainage system and prevent flooding. Research suggests that living walls can reduce energy consumption within the Urban Environment, Transport for London has recognised the benefits of living walls and are implementing green wall technology to several tube stations throughout London. The evidence suggests that green wall technology improves air quality thus benefiting air conditioning within commercial buildings and reducing energy consumption. Green roof technology prevents overheating of the building fabric during the day while cooling the building at night thus reducing energy consumption.