High Performance Building is not a ‘Back of an Envelope’ Calculation


By-lined article by Ian Loughnane, Business Unit Director for Kingspan Timber Solutions

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Following government calls for faster delivery, lower costs and increased sustainability from the 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 – eliminating the gap between design and as-built performance is a key issue within the construction industry. 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 promote best practice.

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. This is what Fabric First and Passivhaus principles are all about – high performance insulation, good airtightness, the minimisation of cold bridging and harvesting 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.

Whilst 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 that this is because U-Values are readily calculated whilst the overall Y-Value can only be determined by 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 we carried out 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.The end result was a fabric first solution, elimination of roof PV and an external wall thickness consistent with the original inefficient masonry design which preserved internal floor space and overall brick cladding setting out.

Another example of this designed fabric based 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.

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The development has a range of house types plus the refurbishment of the original Grade II* listed Hanham Hall. The development is set in twelve acres; at its heart is a green space providing a relaxing and tranquil environment for the residents.

Barratt Homes are keen to determine whether the expected standard of energy efficiency has been achieved and approached the Building Services Research and Information Association (BSRIA) to develop a monitoring scheme. BSRIA will use energy and environmental monitoring equipment, such as the Wi5 data collection hub and conduct a performance evaluation at 185 dwellings at Hanham Hall. 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 will be published.

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

•Air leakage levels routinely 1m3/hour/m2 at 50Pascals of pressure

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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.  As such we await the results from the extensive testing at Hanham Hall with interest rather than fear.”

http://www.kingspantimbersolutions.co.uk

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