Over the years, sustainability has become an increasingly important factor for architects to consider in building design, and it influences their decisions across all aspects of a proposal – including their choice of materiality. In this chapter, I will discuss the many ways in which the use of materials can reduce a building’s negative impact on the environment (during construction, use, and in the future). One sustainable approach to building design is to utilise materials that have been reclaimed or recycled, or at least have the potential to be recycled once the building reaches the end of its life (such as brick, stone, steel, glass and concrete). The use of a reclaimed or recycled material is better for the environment; despite the manufacture of recycled material demanding additional steps over non-recycled materials, the process generates fewer greenhouse gases, uses less energy, and reduces the strain on raw natural resources (that are often non-renewable). Additionally, there is a smaller amount of waste material making its way into the ground and oceans at the end of use. It does, however, mean that the finished products are unfortunately quite often more expensive than non-recycled options. It, therefore, comes down to the designer or architect to make a decision as to which has higher priority: lower build costs or saving resources? Furthermore, recycled and reclaimed materials can have a different aesthetic quality to non-recycled options, which can either be seen as an advantage or disadvantage depending on the designer’s (or client’s) vision for a project. For example, David Chipperfield Architects used recycled handmade bricks to rebuild areas of the Neues Museum (Berlin) that were destroyed in the second world war; they wanted the repaired portions to complement the preserved sections of the building (Chipperfield, 2013, p. 198). Reclaimed bricks often have a different quality to new/ non-recycled; the associated softer textured aesthetic is a result of the less advanced manufacturing techniques used in the past, paired with wear on the bricks from use (Farrelly, 2009, p. 21). In contrast to this, MVDRV opted to use glass bricks in their Crystal Houses project (Amsterdam). On the one hand, the handmade glass bricks (sourced from a company in Resana, near Venice) may not seem to be the most sustainable material choice as they had to be transported across Europe. However, almost the entire shop front is fully recyclable at the end of its life: all of the glass components (including any imperfect bricks and waste material from construction) can be re-melted, re-moulded and repurposed after use (MVDRV, no date). This is an example where an architect has decided to counteract a less sustainable decision with a more sustainable one in order to balance out the negative impact the building has on the environment. Alternatively, renewable resources can be used in building design: this covers everything from materials to water systems and energy sources. The amount of energy required by a building during use (from a non-renewable source) can be dramatically reduced through the incorporation of systems such as ground and air source heat pumps, photovoltaic cells, passive heating and ventilation, and maximum use of natural daylight. While the utilisation of natural daylight and passive systems can be incorporated into the design with minimal cost, inclusion of photovoltaic cells and heat pumps can add significantly to initial costs of a building project, although they will eventually pay for themselves through lower energy bill costs – MVDRV further improved the sustainability of their Crystal Houses project by incorporating a ground source heat pump for optimal indoor temperature all year round (MVDRV, no date). Additionally, the amount of white water used by a building can be reduced through the use of rainwater harvesting, treated recycled wastewater (for use in toilets and irrigation systems) and the installation of water saving taps and appropriately sized basins. Lastly, timber is an excellent example of a renewable material that can be used in a design; ‘it is one of the most sustainable materials in the construction industry’ (Farrelly, 2009, p. 73). Although timber is being used more and more in modern day architecture, it isn’t always the most appropriate or desired material to use – for example, steel is a more appropriate choice in many applications due to its strength and durability.