In the UK, people spend over 90% of a day indoors. On weekdays, when outdoor air pollution concentrations peak in the morning and in the late afternoon, people are usually either in non-domestic premises or on their way to/from non-domestic premises. Therefore, establishing the distributions of indoor air pollutant concentrations in non-domestic environments is essential to model human exposure to hazardous air pollution, especially for vulnerable populations, such as schoolchildren or patients in hospitals. In the Hazardous Air Pollutant Exposure Model of the US Environmental Protection Agency, microenvironment pollutant concentrations are determined by outdoor pollutant concentrations, penetration of outdoor air indoors, proximity of the microenvironment to the outdoor pollutant emission source, and emission sources within microenvironments. Penetration of outdoor air to indoors is related to building characteristics, such as fabric air tightness and ventilation control, which can be affected by energy efficiency retrofits. The aim of this study is to predict the air penetration rate for London’s school buildings (nursery, primary and secondary schools) and enhance our understanding of how energy efficiency improvements will impact indoor air quality modelling so as to prevent potential harmful exposure and improve existing retrofit techniques. The baseline statistics of building physics for school environments in London were aggregated from the building typologies and room uses from 3DStock Model to analyse the effect of built configurations on building ventilation and air tightness. The simulation results show that air change rates due to natural ventilation is low in Post-1980 school buildings, which means recently built or retrofitted buildings that are more airtight and energy efficient need to carefully maintain purpose provided ventilation to ensure adequate air exchange.