My definition is this...

Surprisingly, the UK’s zero-carbon housing policy is one of the most stringent in the world. Policy however, is perhaps the most fragile of promises any governments can make, and turning it into a reality is the real intricacy. With the UK legally committed to reduce its carbon emissions by 80% by 2050 compared to 1990 levels, new homes are to play a vital part (though arguably a high level of savings could be utilised through retrofitting the countries existing housing stock) with the objective that all new homes should be zero-carbon from 2016, and non-domestic from 2019. I was therefore surprised to discover that after years of consultations, there is yet to be a clear definition of what is actually meant by zero carbon.

The closest thing we have to date as a definition is from Level 6 of the Code for Sustainable Homes. Although this has seen a number of exemplar houses by various architects and developers, all have proved difficult to role out into mainstream house building. Any new definition must take into account the difficulties that have been experience through this experiment. This in turn has led to a rethink from the current level 6 requirements. So what is being done to finalise a new definition? The Zero Carbon Hub (ZCH) was set up by the previous government to drive the delivery of zero carbon homes. It aims to deliver across 5 separate areas: energy efficiency of buildings, energy supply, gathering examples, developing skills and consumer engagement. The most immediate step in its remit is to provide a definition, which is expected to be delivered later this year. It is believed that the proposed definition would allow house builders to make half of the emissions savings by improving the fabric of the building and on-site generation technologies.

Defining Energy

In an impressively bold move, the most challenging aspect of zero carbon houses is that emissions should be reduced by not 100%, but actually 150%. Perhaps not the most easily comprehensible or arithmetically correct statistic, but the thinking behind such a figure is admirable. For the first time the measuring of carbon emissions from any new home will include unregulated energy as well as regulated energy. So what are the differences between the two? Regulated energy use includes all forms of energy currently covered in Part L of the building regulations, i.e. fixed lighting, space heating, water heating. Unregulated energy use includes all forms of energy use not currently covered in Part L of the building regulations, i.e. cooking, TV’s, computers, plug-in appliances. Carbon emissions from both must be zero by 2016.

A typical average-sized house built to 2006 building regulations releases just over a combine regulated and unregulated 3 tonnes of CO² every year. This figure is the sum of a buildings regulated (2 tonnes) and unregulated (1 tonne) energy use. Two thirds (2 tonnes) of a typical houses C0² emissions come from regulated energy use – to meet the standard this will need to be reduced to zero (100% reduction). The other tonne, produced from unregulated energy use will also require to be reduced to zero. In the end, overall emissions will need to be reduced by an incredible 150%.

A series of regulatory steps proposed by the government aims to lead the industry towards this goal. Maximum regulated emissions will be gradually lowered from now until 2016, the first of which will see amendments to Part L this October, requiring a reduction of 25% in regulated CO2 emissions (2 tonnes to 1.5 tonnes). In 2013, a further reduction of 44% of 2006 levels, to 1.1 tonne of regulated CO2. Then in 2016, everything must drop to zero, including unregulated emissions.

Zero Carbon Pyramid

The new zero carbon definition will be based on a ‘carbon pyramid’, the foundation of which is the reduction of energy demand. For example, the less energy required for heating, the less dependence on on-site renewable technologies. An airtight and well-insulated home will use little or no energy for space heating.

Energy Efficiency

A specialist task force within the ZCH was set up to advise on a minimum building fabric standard, a

ttempting to keep greens and developers happy alike. The resulting standard describes the maximum energy demand per square metre of floor area per year re

quired within the fabric design. For apartment blocks/mid terrace housing this value is 39kWh/m²/year. Detached, semi and end of terrace houses, where heat lo

ss of is greater, is 46kWh/m²/year.

Carbon Compliance

Additional reductions will come from building based low and zero carbon compliance i.e. photovoltaic panels, solar thermal water heating and heat pumps, biomass boilers, combined heat and power systems (CHP). Carbon compliance covers these technologies that are already available, but which have not yet been forced upon people.

Allowable Solutions

Energy efficiencies made through building fabric improvement and with carbon compliance should reduce a building’s regulated emissions by 70%. That still leaves 0.6 tonnes of regulated emissions, and 1 tonne of unregulated emissions. Still the haziest of responses for this further reduction is a form of offsetting entitled ‘Allowable Solutions. While exactly what these offsets entail is still being determined, current proposed solutions include:

• Carbon compliance beyond minimum requirements, i.e. fabric energy efficiency
• Credits for energy efficient appliances and building control systems to reduce use of appliances
• Exporting low carbon or renewable heat from a development
• Credit for contribution by the developer towards local low or zero carbon infrastructures.
• Improving the energy efficiency in local existing buildings
• Investment by developer into LZC infrastructure – ownership passing on to purchaser of the house.
• Credits for emission savings relative to grid electricity where offset renewable energy is connected directly to the development.

In Conclusion

In a recent conversation with one of Scotland’s largest housing developers (Stuart Milne) regarding the outcomes of their trial Sigma zero carbon home design, they were refreshing honest with regards to the issues that the industry is currently facing. There appears to still be a large disparity between manufacturer’s products performance and efficiency in comparison with their actual results on-site. This combined with an inability to maintain cost efficiency means that we are still a long way off from meeting these future targets. Cost is also incredibly hard to determine in 8 years time. Any new definition must be technically achievable and cost-effective for house builders, which in itself is very difficult in today’s climate where the focus of many house-builders is to stay afloat.

The more time allowed to the construction industry to prepare for what will be extremely stringent building standards, the better. Unfortunately funding for the Zero Carbon Hub has been cut post-definition, in line with every other public department. It is therefore yet to be seen as to whether the level of investment into research and development (and even government financial incentives) required will be in place to translate the zero carbon policy into reality.