The path to 'carbon zero'

The current legislative framework for the reduction of carbon emissions came out of the Kyoto protocol. An agreement signed on the 11th December 1997 by 37 countries, parties to the United Nations Framework Convention on Climate Change (UNFCCC) committing themselves to a reduction in greenhouse gasses in the atmosphere.
 
In response to the Kyoto protocol, the European Parliament and Council on energy efficiency of buildings introduced 'The Directive on the Energy Performance of Buildings' (EPBD) being Directive 2002/91/EC (EPBD, 2003). The Directive came into force on 4th January 2003 and is being implemented by EU Member States. It is a crucial legislative component of the energy efficiency activities of the European Union designed to meet the Kyoto commitment and respond to issues raised in the Green Paper on energy supply security.
 
The UK Government's 'Building a Greener Future' policy Statement of July 2007, set out its target of new homes being net zero carbon by 2016. The UK enforces legislation regarding the energy efficiency of buildings, through the building regulation's 'Approved Document' Part L, in addition the 'Code for Sustainable homes' was introduced in April 2008, to allow developers to market the green credentials of their new homes and provide information to consumers. It sets the standards for 'zero carbon' homes, and was modelled on and largely replaced the Eco-Homes standard, which had failed to spark much enthusiasm amongst  private developers.
 
The rating of new homes against the code became mandatory in May 2008, although it remains voluntary for private builders to apply the code, however contradictory this may appear. In circumstances the developer chooses not have the property assessed, the property is given a nil rating.
 
The code uses a one to six star rating system, with one star set just above the level of the then Part L building regulations, and six stars delivering the highest 'zero carbon' standard.
 
The code comprises nine categories, the last four of which are optional:

• Energy  - Includes an assessment of the building fabric, site or locally installed zero carbon micro generation technologies and also planning issues . 
• Water - an assessment of water conservation measures. 
• Materials - an assessment of environmental impact and the responsible sourcing of materials and finishes. 
• Surface water - and assessment of the management of service water run-off and floor risk measures. 

• Waste - Credits available for household waste recycling facilities and construction waste management. 

 Optional catagories:

• Pollution - Credits available for the Global Warming potential of the insulants used and emissions of NOx from building services. 

• Health and Wellbeing - an assessment of additional lighting and sound insulation, and credits available for meeting the 'Lifetime Homes Standards'. 

• Management - credits available for providing a user guide, and compliance with the 'Considerate Constructors' scheme and 'Secured by Design' standards. 

• Ecology - credits available for the ecological enhancement of the site.

 
For each level a minimum standard is required in each category, with additional credits available to make up the final score. Categories are weighted depending on their deemed importance. It's important to note the 'Code for Sustainable homes' is not a set of regulations, but an award scheme, that is set to become mandatory, but which allows developers to adopt solutions that suit the individual characteristics of the site. Under current legislation, there is a requirement for scheme built with public money or on public land, to achieve level 3 of the code.
 
There is still much debate, in the construction industry, as to whether achieving the onerous requirements of level 6 of the code, will be possible in the mass housing market, requiring as it does a sea change in site practices and construction techniques. It may well bring about a move away from traditional cavity wall construction, to high insulating monolithic construction with render finish or cladding systems,  and a rise in off-site construction methods.
 
Passivhaus
 
Passivhaus is widely considered as the world leading design standard in energy efficient construction. It relies on super high levels of insulation, within an air-tight envelope, fitted with mechanical ventilation.
The Passivehause system was originally developed at the Passivehaus Institute, founded by Dr. Wolfgang in 1996. In principle the passive house eliminates the need for a conventional heating system, by relying on high levels of thermal insulation coupled with passive heat from the inhabitants, electrical appliances, and passive solar heat gain from the sun. The heat that is generated is circulated by the ventilation system, with excess heat similarly expelled, or heat is recovered by a highly efficient heat exchanger, to warm incoming fresh air.
 
As with all solar houses, design to maximize solar heat gain is a requirement, with predominantly south facing glazing and reduced glazing on other aspects. The use of super insulated triple glazing allows for net solar heat gain throughout the year. Attentions to detail is also important, in order to eleimate thermal bridging, and ensure air-tightness is below 1 air change per hour.
 
The Passivehaus standards are currently marketed by the AECB (the sustainable building association) under its CarbonLite Programme.
 

Reference source - The Green bible
 

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