High Performance Building not ‘Back of Envelope’

Following government calls for faster delivery, lower costs and increased sustainability from the construction industry, timber and offsite construction are perfectly placed to meet expanding housing demand. Ian Loughnane, Business Unit Director for Kingspan Timber Solutions, explains why.

Achieving the design performance as detailed in the build specification can present challenges within the construction industry, as can eliminating the gap between design and as-built performance. Developers, architects, engineers and local authorities are beginning to recognise the impact of building details and specification on in-use energy performance and are keen to gain insight into best practice – as was clearly demonstrated at our factory tours.

Whilst renewable technology has its place, there is no doubt that the building energy performance of the external fabric is the most cost-effective and reliable solution. Fabric First and Passivhaus principles deliver high performance insulation, good airtightness, minimise cold bridging and harvest the sun's energy through solar gain via south-facing windows. In essence this means that the building does the work, rather than relying on occupiers operating and maintaining renewable energy devices.

The Value of Energy Performance
Whilst the benefits of Fabric First are well documented, we still find some projects that only specify    
U-values whilst the SAP rating of a dwelling is driven by the interlinked properties of U-values, Psi values and airtightness. I suspect this is because U-values are readily calculated whilst the overall Y-value can only be determined once the building details are known and the individual junction Psi values input against actual junction length. The SAP assessment of a building is now a design exercise of real merit, as a recent exercise with Award Energy demonstrated.

Our initial proposal was based on a U-value of 0.14 W/m2K based on ‘Ultima’ – our patented Kooltherm insulated wall system. This system benefits from excellent Psi values and the SAP exercise demonstrated that an easily achieved airtightness of 5 m3/m2.hr along with a range of Y-values all less than 0.04 allowed us to relax the U-value to 0.16 W/m2K.

Hanham Hall – Energy and Environmental Monitoring
Another example of this Fabric First approach is Hanham Hall – recognised as one of the first zero carbon communities in England. Located on the outskirts of Bristol, Hanham Hall is the first significant development of its type for Barratt Homes and represents a step forward in the development of modern, energy efficient homes. The most substantial challenge at the Hanham Hall development was to design a scheme to meet the stringent requirements of Code for Sustainable Homes Level 6 whilst being acceptable to all stakeholders – hence a structured engagement programme with a wide range of interested parties. The complex brief required an integrated multi-disciplinary team approach from the outset including Kingspan Timber Solutions.

The development has a range of house types set over 12 acres, from one-bed apartments to large five-bedroom houses, plus the refurbishment of the original Grade II* listed Hanham Hall. Prototype units were constructed and tested by Oxford Brooks University for compliance with demanding zero carbon standards. These tests included sound, airtightness and co-heating tests. The prototypes passed with flying colours, vindicating the efforts of all the team to get the details right from the outset.  

Another key feature of the design process was the evaluation of solar gain and air quality. Traditionally, UK regulation has been focused on improving the thermal performance of the external fabric; recently however, a more holistic approach to energy conservation has been adopted. We have now reached a stage where the other side of the coin – heat gain – needs to be designed as part of the process. This was recognised at Hanham Hall and included in the designed energy performance.

Barratt Homes were keen to determine whether the expected standard of energy efficiency was achieved and approached the Building Services Research and Information Association (BSRIA) to develop a monitoring scheme. BSRIA use energy and environmental monitoring equipment, such as the Wi5 data collection hub, to conduct performance evaluation at the 185 dwellings. In addition, ten properties, selected by Barratt Homes, will be subjected to a more in-depth evaluation to further the knowledge and lessons learned from this exercise. The performance evaluation work carried out by BSRIA’s Sustainable Construction Group over the next five years, will include a construction stage assessment that will review the as-designed and as-built SAP assessments, to ensure that there is a consistent baseline for the assessment process. Assessment will include thermal imaging, in-situ heat flux measurements and fan pressurisation testing to measure any changes in airtightness. The houses incorporate a number of features that are not commonplace in UK house design, such as mechanical ventilation and heat recovery (MVHR) and solar shading systems. An early occupation assessment will be carried out to review the information provided to the homeowners and how comfortable they are operating the technology.

For each of the 185 homes, consumption of gas, electricity and water will be evaluated and the additional ten houses will be subjected to more in-depth monitoring including internal environmental living conditions such as temperature, humidity and carbon dioxide (CO2) levels and window/shutter opening patterns, as well as the energy used for hot water, MVHR systems and photovoltaic generation sold into the Grid. The in-use energy and environmental conditioning monitoring data collated and analysed, will be invaluable in assessing the development’s total energy efficiency and also the accuracy of energy predictions for the project.

Occupant satisfaction is an important aspect when measuring the success of a building. The performance evaluation at Hanham Hall will also gather and analyse feedback from the residents via questionnaires and semi-structured interviews. Barratt Homes are one of the first national housebuilders to do a monitoring and evaluation exercise of this kind and on this scale. It is important that the industry continues the development of energy efficient homes and the type of data being gathered on this project will be a critical piece of evidence.

The building envelope was constructed using Kingspan’s patented TEK® structural insulated panel system (SIPS). SIPS are an advanced method of construction, offering superior insulation, structural strength and airtightness over traditional construction methods or systems. SIPS are used primarily in wall and roof applications for residential, industrial, educational and commercial applications, providing energy efficient building structures with proven sustainability credentials.

Achieving High Performance Envelopes
The Kingspan TEK® Building System used at Hanham Hall comprises 142 mm thick structural insulated panels, connected with a unique jointing system for walls and roofs and intermediate floors using I-beams or open web joists. The panels consist of a high performance rigid urethane insulation core, manufactured with a blowing agent that has zero Ozone Depletion Potential and low Global Warming Potential. The core is sandwiched between two layers of 15mm oriented strand board (OSB) – the structural system can achieve: whole wall and roof U-values of 0.21 - 0.10 W/m2K or better and air leakage levels routinely 1m3/hour/m2 at 50Pascals of pressure.

The risk of a performance gap between in use and design is much reduced by adopting a manufactured offsite solution constructed in quality controlled factory conditions. Following a Fabric First approach is also critical to achieving an airtight, energy efficient and comfortable home. As such we await the results from the extensive testing at Hanham Hall with huge interest.

To find out more about Kingspan Timber Solutions visit: www.kingspantimbersolutions.co.uk