Passive Design

Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.

Thermal mass

Thermal mass can be used for passive heating and cooling.

‘Thermal mass’ is the capacity of a material to store heat energy.

In building terms, it reduces temperature fluctuations by absorbing heat when the ambient temperature is hotter than the mass, and then releasing the heat when the ambient temperature falls below the temperature of the mass. When used effectively, this results in improving indoor comfort.

For passive heating, thermal mass works by exposing a high-density material in the building’s interior – such as concrete or stone – to direct sunlight. Often, this will be a concrete slab floor, though it can also be a wall or a specially designed thermal mass element such as a Trombe wall. The sun’s warmth is absorbed during the day and then radiated into the home as the temperature cools at night.

For passive cooling, thermal mass is combined with ventilation – so heat is absorbed during the day, then ventilation is used to dissipate the heat when it is released at night.

To be effective, thermal mass must be considered along with other passive design features such as insulation, location, orientation and layout, window size and placement, and shading.

To ensure that a useful amount of mass is provided within the thermal envelope of the house, designers should use a thermal simulation software tool.


Updated: 09 February 2018