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A CGI of the completed scheme at Dunoon

Actively passive
Published:  22 March, 2010

Gokay Deveci’s house in Aberdeenshire under construction

RTC Timber Systems has developed its own high performance system and the result is Scotland’s first Passivehaus. Peter Wilson, architect and director of business development for the Centre for Timber Engineering at Edinburgh Napier University, reports

Zero carbon may well now be the new black when it comes to the construction of houses in the UK, what with the Code for Sustainable Homes in England and the Low Carbon Building Standards Strategy for Scotland (more usually referred to as ‘the Sullivan Report’) applying the thumbscrews to developers, designers and contractors in the pursuit of low and renewable energy solutions.

The essential difference between the two approaches was Lynne Sullivan and her panel’s eschewing of Code levels 5 and 6 of the Code for Sustainable Homes, the group’s general belief being that, with better standards of airtightness and thermal insulation, Code level 4 was eminently achievable whilst the demands for varying degrees of add-on eco-bling – and costs – inherent in levels 5 and 6 would not be easily recoverable within the conventional housebuilding development process.

The distinction between Scotland and England is interesting because – for at least the past 25 years – platform timber frame construction has been the method of choice for housebuilders north of the border, so much so that, until the recent sudden downturn in construction, timber frame completions were marching towards a dominant 80% of the domestic market.

There have always been sound reasons for this – Scotland’s weather is, to say the least, variable, and the need to get the load-bearing walls up and the roof on and clad as fast as possible has been an important element in the development of an industry that nowadays more than cuts the mustard in the world of off-site modern methods of construction (MMC).

And, as the low carbon agenda grows apace, so too does the potential for increased use of timber frame house construction in England where the technology occupies a much smaller proportion (approximately 17%) of the existing market. Put simply, when market conditions improve, the need to build fast and build well-insulated airtight houses potentially gives the factory production methods of the timber frame industry and its offshoots a distinct edge over traditional construction techniques, the skill base for which is less and less available.

That said, the recent spate of fires on unoccupied and unprotected timber frame construction sites in and around London has unquestionably damaged the image of the sector. If we look beyond the hyperbolic reactions to this problem, however, we can identify a clear need to quickly and effectively transfer the knowledge and experience of this well-tried and tested building technology from north to south.

And there is not only a great deal of construction experience to draw on, but also a considerable amount of design and product innovation taking place that will have significant long-term effects on the efficiency, profitability and sustainability of the industry, not least in the worlds of open and closed panel timber systems.

Take, for example, Elgin-based RTC Timber Systems, which is involved in housebuilding projects across the country. In seeking to achieve higher performance standards, RTC chose to develop its own high performance system tailored to the UK market rather than import established technology from Europe.

The company uses locally-manufactured timber I-beams as the vertical studs in its open panel wall systems, an approach that permits greater depths of thermal insulation to be introduced within the thickness of the wall leaf itself. The company has now developed this further with its patented closed panel wall system it promotes under the trademark title of PassiveWall.

The name is not accidental: RTC has taken on board the lessons of the German Passivehaus system and looked at how they can be applied within the regulatory framework and contractor experience of the UK construction industry. The first serious proofs of the effectiveness of its approach are now emerging – a low energy house in Aberdeenshire (which will be classified as zero carbon once permission for a wind turbine has been secured) has recently been completed using the PassiveWall system. The project has been designed by Gokay Deveci, a professor at the Scott Sutherland School of Architecture in Aberdeen and a long-time leading advocate of zero carbon standards and passive house technology.

Gokay has also been a central player in another RTC project – this time on the wetter west side of Scotland at Dunoon. The waterside development comprises 10 low-energy affordable social homes, nine of which use the company’s open panel I-beam kits. The 10th house was separately designed to meet the Passivehaus standard and uses RTC’s PassiveWall system. In many ways this latter project is a first, not least because it has now been officially certified as Scotland’s first Passivehaus and possibly the first social affordable Passivehaus in the UK.
So what makes the PassiveWall special? The company describes it as “a patent-pending modular cassette-based system that uses timber I-beams for its structure. It can be manufactured in panels up to 12x3.2m and uses novel methods of connection detailing to assure a quick and simple build phase”.

Most importantly, the system was designed to meet all of the latest MMC criteria, which essentially means a high degree of factory manufacture, including the installation of the glass mineral wool insulation that comprises 80% recycled material. The cassettes are exceptionally quick to erect on site, being craned into position on already prepared foundations – a “must” for the largely unseen but very sizeable self-build housebuilding sector in the UK that needs to get its projects wind and watertight as quickly as possible.

And pertinently, the system has been designed to achieve a very high degree of sustainability, with all of the component parts sourced and/or manufactured in Scotland – an aspiration, if not an obsession, for many in these days of searching for the ideal carbon footprint. Applying the old adage “seeing is believing”, the most easily accessible built demonstration of this energy effective, eco-friendly technology will be the project designed by HLM Architects that will be on public view at Scotland’s Housing Expo, the country’s first housing fair that is due to take place near Inverness during August of this year. Before then, you can find the system on stand 2311 at Ecobuild.

PassiveWall is a modular cassette-based system