Gilbert McCarthy, Director of Kingspan Off-Site, provides an outline of the CSH and looks at how house design will need to adapt to meet it.
As Building Regulations and fiscal policy have encouraged the construction of more energy efficient homes, the thermal performance and airtightness of SIPs (structural insulated panels) have helped to establish them as a mainstream building method. The popularity of these systems is set to receive another boost, following the introduction of the latest government initiative to improve the environmental performance of new homes, the Code for Sustainable Homes (CSH).
The CSH has been developed by the government in consultation with the BRE to drive forward a step-change in sustainable homes building practice by setting new standards for the key elements of housing design and construction that affect the sustainability credentials of a new home. The code measures the sustainability of a house design by looking at its performance in nine specific categories and rating the whole house as a complete package. These categories include minimising energy consumption/CO2 emissions, limiting water usage, waste, pollution and surface water run-off, as well as using sustainable materials and maximising health and well-being, management and ecology.
Points for sustainability and environmental performance are awarded to a house design in each of the nine categories and the sum total of the points achieved is converted into a star rating system, which ranges from level 1 (36 points) to level 6 (90 points). In order to deliver consistent improvements in the environmental performance of new build homes, reaching progressively higher levels of the code will become mandatory over the next ten years. Level 3 is to be implemented in 2007, level 4 will be introduced in 2010, level 5 in 2013 and level 6 in 2016.
Reaching the various levels of the code has been kept flexible to enable points to be gained using different approaches to house design. However, certain minimum standards have been set at each level for some categories, such as energy efficiency and water use.
For example, in order for a house design to achieve level 1 it must be 10% more energy efficient than a home built to the 2006 Building Regulations standards. It must also be designed to use no more than around 120 litres of water per person per day. When it comes to achieving level 3, the house design must be 25% more energy efficient than one built to the 2006 Building Regulations standards and it must be designed to use no more than about 105 litres of water per person per day.
At every level of the code, surface water management and site waste management must also be included in the house design, and all materials used in its construction must achieve at least a ‘D’ grade in the BRE’s Green Guide 2007.
While meeting increasingly challenging criteria in the above categories is compulsory in order to reach the different levels of the code, doing so only delivers a small proportion of the total points required by each level. As such, housebuilders need to achieve a large number of additional points for the sustainability and environmental credentials of a house design by incorporating features such as accessible drying space, energy efficient lighting, cycle storage, flexible living spaces and external recycling systems.
Net Zero Carbon Design
Level 6, the highest level in the star rating system, is the standard to which all new homes, both private and affordable, should be designed and constructed by 2016, and it significantly raises the bar in terms of the environmental performance of residential buildings in the UK.
As standard, a level 6 house design needs to be completely net zero carbon. It must have zero carbon energy supply for space and water heating and all electrical power demand for the home, including electrical cooking and appliances.
Thermal performance and airtightness of the building fabric must also be maximised. As such, a super insulated, airtight house fabric, constructed using a high performance SIPs based building system to ensure that the designed heat loss values are achieved in practice, is essential.
A mix of renewable energy technologies, such as a biomass boilers, photovoltaics and solar thermal arrays are an integral part of a level 6 house specification, and it is also beneficial to include mechanical ventilation with heat recovery (MVHR), as well as passive cooling and ventilation.
A level 6 house must also be designed to ensure no more than around 80 litres of water is consumed per person per day, which means that the house design must incorporate a range of water efficiency techniques, such as low volume, water efficient sanitary ware and appliances.
To achieve this level of potable water reduction, around 30% of the water requirement needs to be provided from rainwater harvesting or water recycling systems, such as a stand-alone grey water system, which recycles water from the shower and bath. A reduction in the level of waste generated during construction is another important element of achieving a level 6 house. In addition, all opportunities to help occupants minimise energy use once the house is occupied, need to be exploited, so level 6 homes need to be fully fitted out with low energy appliances, white goods and lighting.
On-going Improvements
Renewable and sustainable technologies, and environmentally sound systems and design features such as these serve to have a very positive impact on the environmental performance of new homes. As such, the drive to implement the CSH standard through levels 1, 2, 3, 4, 5 and 6 will prove very effective in terms of reducing the environmental impact of constructing and running homes, as well as addressing the government’s climate change agenda. While not every house in the short term will be designed and constructed to level 6 of the CSH, it is important that the technology and skills to design and achieve this level of performance are developed and put into practice now to facilitate the transition through all the levels of the code to reach a new standard, which represents the future of housebuilding in the UK.