Timber-based modern methods of construction (MMC) have put down pretty solid foundations in UK housing. But they still have to shake a significant swathe of developers, builders, contractors, specifiers and, indeed, consumers out of the conviction that brick and block is best. Another potential limiting factor on market penetration remains a shortage of appropriate site skills in the historically masonry-oriented British building trade.
The Nu Build initiative at Stoke-on-Trent College aims to tackle both issues; comprising two state-of-the-art German closed panel, ultra-energy efficient timber frame houses, one a show house to demonstrate the quality and performance of a wood-based building, the other a bare bones educational tool for existing and budding construction workers to learn how to build them.
Nu Build came out of Renew North Staffordshire’s 15-year, £2.3bn investment programme to “transform the local housing market”. The aim of the regeneration agency was not only to meet the region’s need for “lots of new housing”, but to help develop a construction industry model that could deliver homes which were both “attractive and affordable”. They also had to meet latest government energy standards and ultimately its target for all new houses to be carbon neutral by 2016. Equally important, the initiative aims to “create new jobs and new skills” for local workers.
To take the project forward, Renew sat down with local construction businesses and, as the educational and skills provider for the whole initiative, the construction department at Stoke College.
Modern methods of construction
According to Ken Burgess, then head of the latter’s engineering and construction faculty, MMC were on the Nu Build agenda early on. “They pressed the right buttons for the whole project and were also an area we wanted to get on our
curriculum,” he said. “They were becoming increasingly relevant, particularly for hitting higher levels of the
government's Code for Sustainable Homes (CSH).”
The initial concept was for Nu Build to comprise three buildings on the Stoke campus: one steel and one timber-framed offsite-manufactured house, plus a site-built timber frame design. This was revised partly due to the West Midlands Centre for Constructing Excellence trimming back the project’s funding, but also thanks to a visit to German offsite build system manufacturers.
“A group of us travelled out and were very impressed with the whole approach, the quality of the finished buildings and the sheer efficiency,” said Burgess. “I started out as an engineer in car manufacturing and the production line methods were home-from-home for me.”
Quality operation
The company that eventually won over the Nu Build ‘mission’ was the Essen-based 80-year-old offsite timber frame specialist Streif.
“The quality of their operation and their houses was a key consideration, but one of the Nu Build objectives was longer term for the housing provider to set up a factory in the North Staffordshire region to employ local people and supply developments in the area and the wider UK market,” said Burgess. “Given the projected volumes of housing needed in the region, Streif expressed an interest in that possibility.”
The eventual deal was for the German manufacturer to supply the core structure of two two-bedroom 86.2m2 houses for around £80,000 a piece, about £50,000 below market price. “They clearly saw the project as a potential showcase for their business in the UK,” said Burgess.
The other partners in the venture were BRE, which advised on the non-Streif elements of the finished buildings and monitored energy performance, and building contractor Kier Partnership Homes, which undertook the foundations and other ground works and completed the houses after Streif’s engineers had put up the timber wall, floor and roof structure.
“Kier hadn't done this kind of house before and saw it as a learning experience,” said Burgess. “It had the perception it was a more expensive approach and saw the project as an opportunity to find out if it could engineer out cost if it adapted it and built large volumes.”
Prefabricated components
The prefabricated wall, floor and ceiling and roof panels were delivered to site, together with the Streif engineers, all the connector bolts and other fixings, in just three trucks. The biggest was a ground floor party wall at 10.16x2.7m.
The 0.18W/m2K U-value outer walls comprised a main structure of 4x2in PEFC-certified softwood studwork and a sandwich from outside in including EPI, mineral wool and Saint-Gobain Metac UF glass fibre insulation, Rigidur H gypsum fibre board, and Tyvek Supro breather membrane. Party walls comprised similar structure, plus Rockwool insulation, while internal partitions were based on an 80mm stud and included Metac UF. The floors included 160mm of rigid Celotex and the first floor construction comprised 22mm of Kunz chipboard on 240mm softwood beams.
The external timber doors and argon-filled, low E glass windows came factory fitted in the wall panels, while internal doors were fitted after erection.
Finally, the roofs included 240mm of mineral wool insulation between rafters, plus 60mm between battens to achieve a U-value of 0.17W/m2K.
UK regulations
For a variety of reasons, the erection of the main structure by the German engineers took slightly longer than normal.
“The key factor was the use of permanent scaffolding, in addition to the 80-tonne crane,” said Burgess. “The Streif engineers were bemused by this as it kept getting in the way. In Germany they would have just used the crane and temporary tower scaffold, but Kier insisted on scaffolding throughout to satisfy UK regulations.”
Despite this, the Streif team still had a weather- and airtight shell up in just four days – and you can see
it shooting up on a time-lapse film on the college website (www.stokecoll.ac.uk/osm).
“It was really just a bolting together process,” said Burgess. “As an engineer, I was particularly impressed with the specialist tools and metal fixings Streif has developed for the job, and the precision. The base dimensions had to be accurate to 3mm.”
Streif homes can be finished in any skin, including brick to suit UK tastes, but Nu Build opted for a very German mix of Alsecco polymer render and larch cladding – and the whole structure was finished in two weeks.
Heating technology
The houses were equipped with Ventaxia MVHR units and Vaillant solar water heating systems and Ecotec Plus 612 condensing gas boilers for the underfloor central heating system, which runs under a screed on the ground and first floor.
Depending on securing the sponsorship, Nu Build might also add some photovoltaic panels. Even without these, the combination of the Nu Build houses’ airtightness and inherent insulation performance, plus the renewables they already have, adds up to very energy-efficient finished structures.
“We didn't actually go through the BREEAM auditing process, so we can't make any official claims," said Burgess. "But BRE told us that, technically, we'd achieved CSH Level 4.”
Learning opportunity
The interior finish in the teaching home is minimal so that students and builders from local companies can see the mechanics and components of the structure. The showhouse, by contrast, is fully decorated, carpeted and furnished to a ready-to-move-in standard, but is also plastered with posters explaining how it was built and what’s going on beneath the skin.
“This one is designed to give developers, specifiers and consumers an idea of what it would be like to live in,” said Burgess. “But they can also kick the tyres.”
Largely thanks to the credit crunch and construction slump, some of Renew’s and Nu Build’s wider aims haven't come to pass. Other prospective MMC projects they hoped to be involved in at Stoke’s Waterside Development and in Crewe, with Nu Build acting as an education and information hub, are still on hold. Streif hasn't built a factory here yet either. But the Nu Build site itself is being put to good use as a training facility by students and builders. It is also busy hosting school visits and seminars for construction professionals and specifiers with such titles as Designing for the Future and Energy Efficiency through MMC.
“Not everything we intended for Nu Build has happened yet,” said Burgess. “But for me it’s still a success. We've got an excellent training facility and, equally important, a tool for winning over the hearts and minds to MMC of people who still think there's nowt like a traditional brick-built house!”
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Education is at the heart of the Nu Build project |
