Cracking the code

Gilbert McCarthy, managing director of Kingspan Off-Site, looks at the benefits of using off-site timber frame systems to crack the code for sustainable homes.

AS ALL new public sector homes must now meet level 3 of the Code for Sustainable Homes (CSH), choosing the right house design and building materials is vital. Advances in timber frame technology make it ideal to achieve the requirements of the code.

Implemented to drive sustainable building practices forward, the CSH, introduced by the government in 2007, sets 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, to produce a rating for the house as a complete package. These categories address energy consumption/CO2 emissions, water usage, waste, pollution and surface water run-off, as well as the use of sustainable materials and maximising health, well-being, management and ecology.

Points for sustainability and environmental performance are awarded to a house design in each of the nine categories, with the sum total of the points achieved converted into a star rating system ranging from level 1 (36 points) to level 6 (90 points).

To ensure consistent improvements are made in the environmental performance of new build homes, higher levels of the Code will become mandatory over the forthcoming years. Currently all new homes must reach level 3, while level 4 will be introduced in 2010, level 5 in 2013 and level 6 in 2016.

Cracking the Code with timber

Reaching the various levels of the Code has been kept flexible to enable points to be gained using different approaches to house design. This also ensures that all types of construction continue to evolve to meet the CSH, minimising the risk of relying on one building method.

Key to achieving level 3 and upwards of the code is the choice of materials for all the building elements. Based on the BRE’s Green Guide, a number of credits are available when addressing the environmental impact of the building material, over its entire lifespan. With timber now widely used from sustainable sources, timber frame building systems can score highly in the environmental categories of the CSH.

Selecting the right building materials is also important to maximise the thermal performance and airtightness of the building fabric of a house, which is required to achieve Code level 3 and above. Off-site timber frame building systems, such as structurally insulated panels (SIPs), provide an ideal method of creating air-tight, thermally efficient homes. Pre-insulated timber frame panels, combined with an effective jointing system, can deliver excellent results for air-leakage testing. Delivering a U-value of just 0.20W/m2K, the energy efficiency of walls built using SIP panels reduces household bills and lowers greenhouse gas emissions by up to 40% compared to traditional build methods.

Although energy efficiency accounts for a relatively large proportion of the credits (36.4% or 29 credits) required to reach level 3, sustainability and the environmental performance of a house design also have significant roles in the code level assessment. Pre-insulating timber frame panels with materials such as urethane, which have a zero ozone depletion potential, enhances the environment credentials of the house design and maximises the thermal efficiency of the building envelope. Using CFC/HCFC-free insulation materials with a low global warming potential in timber through-wall systems can add points to the CSH assessment.

The environmental impact of the construction process can be reduced further using off-site timber frame building systems. As an estimated 13m tonnes of completely unused building materials are discarded as waste every year, CSH credits are awarded for on-site waste management. Off-site manufacturing of timber frame systems ensures that the building elements are delivered to site as designed, negating the need to make on-site adjustments, which can create unnecessary waste. Moreover, as the panels are supplied ready for immediate installation, the waste generated from packaging is eliminated.

To level 4… and beyond

To achieve code level 3, a house must be 25% more energy efficient than a home built to the 2006 Building Regulations standards. In order to reach level 4, these energy savings must be increased to 44%. Effective insulation and air-tightness of timber frame building systems can only economically provide a proportion of the credits required to meet code level 4. Therefore, renewable options must be incorporated into the house design to gain the 44% energy reduction.

Net-zero carbon housing

By 2016, all new homes will have to be designed to reach Code level 6. As the highest level in the CSH rating system, level 6 significantly raises the standard of the environmental performance of residential buildings. A level 6 house design must be net-zero carbon, including the energy required for space and water heating and all the electrical power demands of the home.

In order to achieve this, the thermal performance and air leakage of the building fabric can be maximised using SIP based systems. However, building services must be integrated to optimise efficiency and a comprehensive platform of renewable, sustainable and water efficiency technologies must be incorporated into the house design.

Off-site timber frame building systems can significantly improve the insulation, air-leakage and sustainability of a house design. Achieving the higher levels of the code is made more achievable if these systems are integrated with renewable technologies. Combining innovative timber frame systems with low carbon technologies will enable the housing industry to achieve the requirements of the code and move towards a sustainable future.