02 April 2012

Sustainability is about energy efficiency and more

Clay brick has, inherently, a number of performance attributes that, taken together, make it one of the most appropriate building materials in terms of sustainability. 

Leading manufacturer of clay bricks, Corobrik, suggests that, "Achieving sustainability in today’s commercial world requires the balance between non-sustainable inputs to produce a product and the sustainable outputs from the performance of the product in application, to be in favour of the outputs in the economic, social and environmental dimensions.”

With clay brick the sustainable value afforded by the product’s performance in application well outweighs the non-sustainable ‘costs’ of the inputs, endorsing clay brick as an environmentally friendly building material that can contribute to a more sustainable environment in the future. 

One of the key attributes of clay brick is its durability. It has the longevity to perform beyond a 100-year lifecycle – eliminating the carbon debt associated with the replacement of less durable walling materials. Further, clay brick’s longevity provides for the brick’s embodied energy to be amortised over its lifecycle. 

A further attribute, confirmed by scientific research, is that the inorganic qualities of fired clay fulfil the requirements in terms of building materials to support healthy living. The mineral content of fired clay guarantees a nearly pollution-free quality of indoor air. It absorbs and releases humidity from the atmosphere, providing a good moisture balance inside buildings for healthy living. It is not a food source for mould, which is widely recognised as a major cause of ‘sick building syndrome’, and being a dry material, it offers protection against mould growth. Fired clay also provides a high level of acoustic insulation. It is incombustible and, being benign, does not release toxic fumes under fire conditions. 

In addition, maintenance-free clay face brick incurs no future carbon debt associated with a lifetime of maintenance. It offers colourfast aesthetics of natural hues and organic textures that sit well in natural and built environments. 

Clay brick is a user-friendly material with a human scale. It is both reusable and recyclable and if it is returned to landfill – this is akin to returning the brick back to its source. 

Corobrik also highlights clay brick’s natural thermal performance properties which support thermal comfort inside buildings for longer and contribute to optimal energy efficiency and lowest total energy (embodied and operational) over the lifecycle of residential buildings across South Africa’s six major climatic zones. According to Corobrik, this is validated by numerous scientific studies. 

The Energetics Australia Full Lifecycle Assessment of the total embodied and operational energy used by two house types built in three locations and in four orientations using five different walling systems, found that no matter the construction type, the embodied energy of the houses comprises less than 10% of the total energy used over a 50-year lifecycle. Of the 90% attributed to operational energy consumption, 40% is consumed in the heating and cooling of the house to achieve target thermal comfort conditions. This finding emphasises the importance of using thermally efficient building envelopes to reduce energy consumption. 

The Energetics Australia study and others established that double skin clay brick walls with the appropriate level of resistance (insulation) between the brick skin provided for lowest cooling and heating energy usage, when compared to lightweight walling that relies on a high R-value alone to achieve energy efficiency. The studies found that the exclusion of thermal mass from the walling envelope resulted in suboptimal thermal outcomes, compared to the best of the double skin clay brick options. 

The best of the double skin clay brick walled alternatives was found to provide the lowest total energy usage (embodied and operational) over a hypothetical 50-year life cycle in all instances. 

Another conclusion of the Energetics Australia study is that it makes sense to build houses that are durable so that the energy inevitably used in the construction is not wasted, because the house remains in use beyond 50 years. Clay brick more than meets this requirement for durability. 

Emphasising the significance of thermal mass, Corobrik says that all major studies recognise that achieving optimal thermal efficiency over the life of buildings begins with the application of sound passive design principles, involving correct orientation, shading and ventilation as well as the use of thermal mass in the building envelope. 

These studies recognise too, that thermal mass is particularly relevant in South Africa’s climate, characterised by long hot summers, where the challenge for walling materials is to moderate high external temperatures to more bearable levels indoors, while also ensuring that the average indoor temperature remains at an acceptable level throughout the year. 

More recent research in respect of the ‘CR product’ of walling envelopes and energy efficiency in houses has determined that the optimal walling system will have sufficient levels of ‘C’ (thermal capacity as derived from mass) and be supplemented with appropriate levels of ‘R’ (as provided by the air in the cavity or insulation in the cavity or both). Generally, the higher the CR product of a walling system, the greater the level of thermal comfort experienced throughout the seasons. Clay brick walls can be specified and built to offer CR product values appropriate to achieving lowest lifecycle energy usage most cost-effectively. 

Where inadequate ‘C’ is provided, as with insulated lightweight walling envelopes associated with lightweight building system technologies, there is little or no propensity for the wall to ‘self-regulate’. Thermal modelling shows how such walls cause a ‘hot box’ effect inside during the hot summer months, resulting in the greatest thermal discomfort and highest cooling energy usage. 

Corobrik’s view is that clay brick is a unique building material, tried and tested, and proven as now more relevant than ever in addressing the sustainability imperatives of the times. It offers a host of performance attributes that make it a holistically sustainable building material.