Performance of medium-rise, thermally lightweight apartment buildings during a heat wave

There is growing evidence that medium rise, thermally lightweight, well-insulated, naturally ventilated, single apartment blocks are at risk of overheating especially when sited in the SE of England. This paper reports the thermal comfort and heat stress conditions recorded in 15 apartments located in North London on the outer fringes of the urban heat island. The apartments were built using off site, light gauge steel prefabrication methods. Bedrooms on floors one and two and on floors seven to eleven were monitored for 22 days during July and August 2013, a period that included a heat wave, which precipitated a level 3 heat wave alert. The risk of overheating was assessed using the static criteria in CIBSE Guide A and the three CIBSE TM52 adaptive thermal comfort criteria. Heat stress levels in one room were assessed using the Humidex and Heat Index metrics. The bedrooms on floors one and two did not overheat whereas all the apartments on the upper floors failed both the static and the adaptive criteria producing conditions that would lead to heat stress. The results strongly suggest that the design, ventilation and servicing strategy, combined with the inherent fragility of thermally lightweight and well insulated construction, is inappropriate in some areas of the UK and may even be dangerous in hot summers. The findings have significance for construction companies, landlords and social housing providers and those concerned with construction guidelines and the building regulations.