Construction World October 2015

Brick buildings

for a better world BRICK BUILDINGS

Addressing all the basics for affordable quality living, with safety and security a given, clay brick in construction has demonstrated the flexibility to work well with all design styles to bring authenticity and appealing human scale to buildings. But it goes much further than that to afford opportunity for lowest heating and cooling energy requirements that translate into low total (embodied + HVAC energy) Greenhouse Gas emissions over a 50 year lifecycle. To this end, the world’s consuming focus on energy efficiency has led the clay brick industry to research how designers may simply and cost effectively better work with nature to take the wonderful thermal properties of clay brick in construction to new levels of thermal comfort and lower heating and cooling energy usage in all six major climatic zones of South Africa. The net conclusion from all the research is that clay brick walling can be specified to deal with the peculiarities of the different climatic zones in ways that insulated lightweight walling cannot. This provides brick walling options that will outperform insulated lightweight walled buildings specified in compliance with SANS 204 Energy Efficiency Standards and SANS 517 required for Light Steel Frame building. In that process and following deemed to satisfy requirements, clay brick walling can be specified to offer the highest levels of thermal performance this facilitating lowest lifecycle energy costs and low total lifecycle carbon footprints. This can be provided using insulation with a lower R-value than Simple clay brick construction, the long-time benchmark for all that is good about housing and social infrastructure buildings in South Africa, goes beyond the important fundamentals of durable, low maintenance structures with enduring aesthetic integrity to afford comfortable thermally efficient accommodation in which South Africans live, work and play.

required for lightweight to ensure best returns for the cost of any insulation applied. The thermal mass inherent in clay bricks is what brings the ‘X’ factor to the thermal efficiency equation as shown in Figure 1. The net benefit of the slow transfer of heat (6 to 8 hours) to the inside is that the hottest part of the day will have passed before the heat impacts on the inside. This facilitates superior day-time thermal comfort conditions and lowest cooling energy usage compared to insulated lightweight walls that have no propensity to self-regulate. In the case of insulated lightweight the outside heat impacts on the inside in approximately one hour, the heat flux on the inside coinciding with the hottest part of the day outside leading to comparative discomfort and greater need for cooling energy. Clay bricks on the inside add further function to slowly absorbing and storing heat from the internal air as day time temperatures rise this further moderating internal temperatures, helping keeping the house comfortable for longer, requiring less cooling energy. In winter the energy from lower angled sun radiates in through the windows, the internal thermal mass then functions to slowly absorb and store radiant heat during the day that is then released in the evening as the cold night air impacts on internal conditions, helping keep the house warmer for

Figure 1 represents the heat flux through a double skin cavity brick windowless wall in summer. Of the 700 to 900 W/m² that impacts on the outer surface just 5 to 6 W/m² finally passes through the wall to the inside. The thermal lag played a key role in limiting the magnitude of the maximum and minimum internal temperatures. The study showed that cavity brick reduces the heat transfer by absorbing and storing the heat in the external brick leaf, then radiating it back to the outside environment, thereby reducing the net heat flux across the wall.

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sustainable construction world