The energy-efficient house: all about thermal mass

An energy-efficient house located in a temperate climate will include materials that provide "thermal mass," that is, materials that will store heat readily and cool down very slowly. These tips will help you understand the importance of thermal mass and how these materials can help reduce your energy costs.

Concrete floor slabs are an example of a material with a high thermal mass. Brick and stone also have high thermal mass as does water, which has a heat-storage capacity five times that of brick. Materials with high thermal mass are best used inside the house where they are exposed to winter sunlight through south-facing windows, but shaded by the eaves from direct summer sun.

The thermal mass, such as a brick or stone wall or a concrete floor covered with ceramic tiles, slate or hard vinyl, will soak up heat like a sponge during the course of a winter day and then gradually release it throughout the night, helping to maintain a comfortable room temperature.

A concrete slab floor has the benefit of the earth below to help maintain it at a stable temperature. In summer, the floor slab or wall will be shaded from the sun by the eaves and maintain a lower temperature than its surroundings, so that it will exercise a cooling effect on the interior. Floor slabs should be left uncovered in summer so that the maximum amount of heat can be absorbed and released. To maintain comfort, such a floor can be covered in carpet or rugs during the winter.

When a house has enough thermal mass in the south-facing rooms, and effective insulation in the roof and external walls, it will use less energy for heating and cooling and will be more comfortable in all seasons. Insulating materials placed in the roof and walls contribute significantly to the energy efficiency of a house by excluding unwanted summer heat and by ensuring that heat collected through windows during the course of a winter's day is not allowed to escape quickly at night.

The roof space should be treated with bulk insulation, such as glass-fibre batts or loose fill, placed on the ceiling.To further reduce the penetration of summer heat through the roof, a reflective foil laminate may be installed on the rafters under the roofing battens. To achieve maximum energy efficiency, all external walls of a house also should be insulated. The proper insulation (such as foam) placed in the cavity of a double brick wall or behind the lining of other forms of wall during construction will reduce heat gain in summer and heat loss in winter.