Thermal mass

Highly insulated buildings have a tendency to overheat in summer. An appropriate amount of thermal mass, combined with shading and controlled ventilation is essential to provide a buffer against overheating.

Thermal Mass

Thermal mass in the walls, floors and ceilings should be exposed to the internal spaces. Heat will be absorbed from the air during the warmest part of the day reducing the internal temperature. The heat absorbed is then released from the mass at a time when the external temperatures are cooler, usually during night. Thermal mass effects work best with significant daily temperature ranges. Thermal mass causes both a time lag and a reduction in both temperature peaks and troughs.

Thermal Mass

Building fabric can be used to stabilise internal temperatures, absorbing heat when temperatures rise and emitting heat when they fall. Thermal mass can be used more effectively by extracting the heat during warmer periods. This can be done by passive means, for example, ventilating the building during the cooler night period. Or, it can be done actively, by passing chilled water or air through the fabric to remove the heat.

What should I do?

Ensure that thermal mass has been considered and has been modelled by design consultants where relevant.

WLGA - CLILC Llywodraeth Cynulliad Cymru / Welsh Assembly Government