16 November 2010

Consider thermal mass rather than R-values alone

While historical buildings remind us of the enduring and aesthetic attributes of clay brick in architecture, the current focus on global warming, the need to optimise energy efficiency in buildings and the renewed interest in passive solar design principles are all reminders of the thermal properties of clay brick walling.

As governments set targets to reduce greenhouse gas emissions and electrical energy usage, various scientific studies have been initiated to determine the material combinations and those material properties that are best able to optimise the thermal performance of buildings. Recent empirical research and thermal modelling studies of walling envelopes all correlate in endorsing the importance of thermal mass – and specifically that of clay face brick walling – in achieving optimum thermal outcomes, lowest energy usage and lowest lifecycle cost for different house types in climatic zones typical of South Africa.

The research essentially counters the European mindset that the insulation properties of building materials are all-important in determining the thermal performance of buildings. This argument suggests that ‘the greater the insulation (or thermal resistance) properties of materials, the greater will be the level of thermal comfort and the lower the energy need for mechanical heating and cooling’. However, the research studies indicate that lightweight materials without thermal mass will provide ‘suboptimal’ thermal performance outcomes for houses in South Africa, compared to the same constructed with heavy mass clay brick walling.

In all the studies, thermal mass proved to be the key thermal performance property. Houses constructed with double skin clay brick walls, with different levels of resistance appropriate for the climatic zone, consistently provided optimal thermal outcomes compared to the lightweight walling alternatives, even with their high R-values.

As a leading manufacturer of clay brick in South Africa, Corobrik says that the substantive thermal benefit that clay brick provides should be considered together with research that has established that clay brick walls afford the lowest lifecycle energy cost, and the full Lifecycle Assessment – undertaken by Energetics at the University of Newcastle in Australia – which found that double skin clay brick walled houses provide lowest lifecycle carbon emissions (embodied energy and operational energy) over a 50-year lifecycle.

In addition, clay bricks are made of an incombustible, inert material that releases no CFCs or VOCs under normal or fire conditions; clay face bricks provide enduring, warm colours and textures and an appealing human scale; and they deliver the lowest lifecycle maintenance cost – eliminating the carbon debt associated with a lifetime of maintenance. Furthermore, the record of houses built with clay brick stretches back hundreds of years. Corobrik suggests that when all these factors are considered in a holistic perspective of sustainability, double skin clay brick walling with face bricks, cannot be beaten.