C hapter 04: Strateg i es fo r g reen i n g so c i a l ho u si ng
Low impact materials and construction techniques There are a number of factors which classify building materials as sustainable. Before and during construction, materials are deemed environmentally sustainable when the embodied energy is lower than customary materials. Embodied energy is the total energy used to create a building product including all the processes involved in harvesting, production, transportation and construction. It can represent a significant proportion of the total energy used during the lifecycle of a home. Such measures as using local materials, minimal processing, reusing existing structures and materials and using renewable materials (which are quickly and easily replaced) are ways to ensure that embodied energy is low in a building. Environmental sustainability is not simply a function of energy use in the life of a building but also considers the health of the occupants and those involved in the construction and deconstruction processes. Furthermore, to maximise the environmental benefit of the material the construction techniques must be used to achieve the passive design strategies outlined in Section 4.1.1.
Materials and methods for structure and envelope of the building §§ Rammed earth construction: For the construction of walls, earth-based technologies offer ideal solutions for long-term sustainable construction programmes in dry climates. To create a rammed earth wall, formwork is assembled and layers of earth are compacted within the forms. Compacting of the earth is
52
Green building interventions for social housing
either manual or pneumatic and can easily be done through for community participation. Construction must be done in dry weather (Fielding et al., 2012). §§ It is important to protect earth buildings from water (e.g. standing water and rainfall). To protect rammed earth and adobe buildings from water the following steps can be taken: §§ Chemical additive (e.g. mortar-proof ) to inhibit water absorption in render – due to cost additive can be limited to external ‘splash zones’ of walls §§ Requires sufficient roof overhang and stone or concrete foundation to raise earth construction above ground §§ Damp-proof course should be considered to protect the earth wall from moisture rise §§ Stabilising agents (e.g. cement) can be used but have the drawback of increasing the embodied energy of the construction §§ Stabilised soil blocks and interlocking stabilised soil blocks: There are many options when it comes to earth or soil blocks. The amount of stabiliser (content of cement), type of stabiliser, method of production, form of the blocks, and use of waterproofing agents can all vary in the production of soil blocks. It is possible to produce between 250-350 SSBs in a day using a simple block press. SSBs depending on method and content can be 70 per cent less energy intensive than fired bricks and 20-40 per cent less expensive. There is also the environmental savings with no fire wood use (Montgomery, 2002; Minke, 2006; UNHabitat, 2012a).