Policy 5.9 Overheating and cooling
A The Mayor seeks to reduce the impact of the urban heat island effect in London and encourages the design of places and spaces to avoid overheating and excessive heat generation, and to reduce overheating due to the impacts of climate change and the urban heat island effect on an area wide basis.
B Major development proposals should reduce potential overheating and reliance on air conditioning systems and demonstrate this in accordance with the following cooling hierarchy:
1 minimise internal heat generation through energy efficient design
2 reduce the amount of heat entering a building in summer through orientation, shading, albedo, fenestration, insulation and green roofs and walls
3 manage the heat within the building through exposed internal thermal mass and high ceilings
4 passive ventilation
5 mechanical ventilation
6 active cooling systems (ensuring they are the lowest carbon options).
C Major development proposals should demonstrate how the design, materials, construction and operation of the development would minimise overheating and also meet its cooling needs. New development in London should also be designed to avoid the need for energy intensive air conditioning systems as much as possible. Further details and guidance regarding overheating and cooling are outlined in the London Climate Change Adaptation Strategy.
D Within LDFs boroughs should develop more detailed policies and proposals to support the avoidance of overheating and to support the cooling hierarchy.
5.47 London will experience higher average temperatures. This is likely to intensify the urban heat island effect – the way higher ambient temperatures are experienced after sunset in urban areas in comparison with rural areas. This is most intense at night and in London is principally experienced within the Central Activities Zone, as buildings and roads absorb more solar radiation than green space and vegetation. Combined with man-made heat emissions, this can make the centre of London up to eight degrees warmer than the Green Belt on hot summer nights. The GLA is developing with the Chartered Institute of Building Services Engineers (CIBSE) guidance for developers to address the risk of overheating in buildings. The guidance will allow developers to take a risk-based approach to reducing overheating by providing different future hourly weather data to use in building simulation models. These take account of the location of the development with respect to the urban heat island and how sensitive the proposed use of the development is to overheating. The Mayor encourages the use of this guidance in the preparation of development proposals.
5.48 The cooling hierarchy in Policy 5.9 seeks to reduce any potential overheating and also the need to cool a building through active cooling measures. Air conditioning systems are a very resource intensive form of active cooling, increasing carbon dioxide emissions, and also emitting large amounts of heat into the surrounding area. By incorporating the cooling hierarchy into the design process buildings will be better equipped to manage their cooling needs and to adapt to the changing climate they will experience over their lifetime.
5.49 In accordance with sustainable design and construction principles, development proposals should maximise opportunities to orientate buildings and streets to minimise summer and maximise winter solar gain; use trees and other shading; increase green areas in the envelope of a building, including its roof and environs (see Policy 5.11); maximise natural ventilation; expand green networks across London (see Policy 2.18); and wherever possible incorporate a range of public and/or private outdoor green spaces. The Mayor fully supports urban greening initiatives and further policies are outlined below and in Chapter 7.