Sustainable Design

 
Sustainable design has come to encompass a broad range of issues, beyond the reduction of energy use or the addition or add-on renewable energy technologies.
 
For the purposes of this brief introduction, we will touch upon a number of other equally important issues:

• Ethical and sustainable sourcing of materials
• Choice of materials and Embodied energy
• Location, planning and design
• Water conservation
• Design for de-construction and recycling

 
Ethical and sustainable sourcing of materials
 
Preference should be given to materials from renewable resources, such as timber, straw, or resources that are in abundant supply, such as earth or clay.
 
Timber is re-emerging in building construction, partly because of its green credentials, however, much timber comes for the illegal logging of Tropical Rain Forests. 80 percent of ancient forests has already disapeared, half of which in the last 30 years alone. Timber should only be sourced from supplies that are certified from the Forest Stewardship Council (FSC) or the Program for Endorsement of Forest Certification. This provides some assurance the timber has been harvested in a sustainable way, involving the management and replanting in a socially and environmentally sustainable manner.
 
Wherever possible materials should be sourced locally, much energy is currently expended in transporting building materials from abroad, currently most timber is imported.
 
Choice of materials and embodied energy
 
There is increasing evidence that emission of Volatile Organic Compounds (VOCs) from paints, preservatives, fire retardants, and synthetic fibres contained within household furniture, is a health hazard and some may be carcinogenic. They are derived from fossil fuels in increasingly short supply, and the energy required for their extraction and processing is high. There is an option to return to traditional paints and finishes of yesteryear, Silicate coatings and resin paints, and limewash for the exteriors, distempers, casein paints oil and resin emulsions and clay paints for interiors to name but a few, The paints have the added advantage of being vapour permeable, so allowing the wall to breath, and trapped moisture to escape. Breathable walls are inherently good at modifying humidity levels, helping to maintain comfort levels for the occupants.
 
The use of lead on roofs can lead to heavy metal contamination in water run-off, eventually affecting groundwater and ultimately watercourses. A number of lead free alternatives are currently available on the market.
 
There remains some debate over the effect of electromagnetic radiation from electrical wiring, with strong evidence of the harmful effects associated with pylons and transmission wires. Magnetic fields can be reduced by the use of radial or spur circuits in place of the ring main in common use, at the expense of increased wiring and circuit protection devices.
 
At the present time, where cost in use is the main driving factor with regard choice of materials, the effect of embodies energy with regard the choice of insulants can be safely ignored, however as we move closer to ˜carbon free" buildings,  the embodies energy will represent an ever increasing percentage of the overall energy equation, favouring natural insulants like sheep's wool and straw bale. These materials are low in embodied energy when locally sourced.
 
Cement has relatively low embodies energy, however, because of the scale of production it still represents 7-10% of the world output of CO2, the third largest emitter of CO2 after the transportation and power generation sectors. There are several ways to reduce CO2 emissions, namely the mixing of cement with other pozzolanic material, such as fly ash slag. The production of aerated concrete blocks reduces the percentage of cement over conventional aggregate blocks, for a given wall area, while the blocks have good thermal insulation qualities, they are of low compressive strength, limiting their structural applications. Carbon sequestration from the gaseous by-products from the cement kilns is also possible. There are also several alternatives to cement, of which lime in its various forms is the most obvious choice.
 
Limes mortars should be favoured over cement mortars as lower temperatures are required for their manufacture, hence less fossil flues is used in its manufacture. With both the production of lime and Portland cement, CO2 is released during the burning of the raw materials, however in the case of lime, approximately the same amount of CO2 is reabsorbed from the atmosphere during the set, which cannot be said of Portland cement.
 
The use of crop products, such as timber, straw, reed, flax and hemp as building materials, all lock in the CO2 that has been taken in during growth, wide scale use of these products can therefore be considered as a CO2 store. Where suitable management or farming methods are in place, there production is entirely sustainable. However a holistic approach needs to be adopted, with regard the design of the whole building, natural materials need to be able to breath, so any moisture can escape, it is preferable to use lime or clay based renders and plasters, which are vapour permeable, these materials are also more forgiving, and can accommodate the inevitable settling and movement on site, without cracking and permitting the ingress of water.
 
 
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