The University of Pretoria has released results of its thermal performance study, which assessed the operational energy usage of structures built with six different walling materials across six South African climate zones.

Annual operational energy is the sum of all heating, cooling and ventilation electricity costs accumulated over one year. Measurements were based on the residents living in reasonable thermal comfort of between 19˚C and 25˚C.

By referencing this study, architects can make informed decisions about walling material specifications and design high-performance structures that reduce reliance on expensive electricity.

Building types
Because the size of a building influences its thermal performance, three building types were analysed:
• A large 2 000m2 commercial building.
• A middle-income residential home of 130m2.
• A low-income home of 40m2 (with heating fuelled by paraffin).

Variables such as floor, roof, windows, doors and occupancy patterns were kept constant.

Wall types and materials
Six wall types were analysed:
1. Solid double clay-brick wall, internal and external (220mm thick and plastered).
2. Uninsulated double clay-brick cavity wall (270mm thick with a 50mm air cavity).
3. Insulated double clay-brick wall (280mm thick, 30mm insulation in the cavity).
4. 140mm hollow core concrete block (150mm thick, plaster/bagged).
5. Light steel frame, externally clad with 9mm fibre-cement board to SANS 517 (145mm thick with vapour membrane, strand board plus internal gypsum board with insulation).
6. Timber frame to SANS 10082 clad with external weatherboard (145mm thick with strand board and plasterboard internal cladding).

The best and the worst
The lowest energy use was found in:
• Residential buildings in all climate zones with thermally insulated 280mm clay-brick cavity walling.
• Non-residential building in climate zone 1, built with 140mm hollow concrete block walling.
• Non-residential building in climate zones 2 to 6, built with 220mm solid clay brick walling.

The highest energy use was found in:
• Residential buildings across all climate zones with 140mm hollow concrete block walling.
• Non-residential building in climate zone 1 with timber frame walling.
• Non-residential buildings in climate zones 2 to 6 with light steel frame walling.

The Clay Brick Association of South Africa
Tel: 011 453 5229
The annual electricity consumption of six different walling types in a 130m2 home.