Sweet SIPs of success

Mark Cantrell explores an innovative building system that is making its mark in the Design for Manufacture competition.

When the Crest Nicholson-led SixtyK consortium scored its third hit and scooped the last available site in the Design for Manufacture competition, it owed much of its success to a concept that means houses will be delivered to the sites in kit form. The heart of the SixtyK Consortium’s “kit” is the TEK building system, which is based on structural insulated panels (SIPs) and manufactured by Crest Nicholson’s SixtyK partner Kingspan Century. The company is said to be one of Europe’s leading manufacturers of timber-based building systems and is working with Crest alongside members Arup, Davis Langdon, McFarlane Wilder and Sheppard Robson.

Entrants to the competition had to meet some exacting criteria, not least the maximum build cost of £60,000 per house without skimping on quality, but they also had to offer design flexibility, affordability, be adaptable, and meet some stringent energy efficiency and low carbon targets for the EcoHomes standards.

The Design for Manufacture competition was launched last year by deputy prime minister John Prescott, and was managed by regeneration agency English Partnerships. Ten sites were up for grabs and with the allocation of the final site SixtyK has won more ground than any other entrant. SixtyK will build 441 new homes across the three sites. The first at the former Linton Hospital site in Maidstone, Kent will see a total 148 homes constructed. Of these, 30% will be allocated for social rent and for first-time buyers. Renny Lodge in Newport Pagnell, Bucks, was the second site, and this will feature 68 homes, again with 30% built as social housing to competition standards. The final site is that of the former Rowan High School in the London Borough of Merton. This will include 227 houses built to the competition standards. The scheme also includes 32 units in the refurbished school building, a doctor’s surgery and a community hall. Work is expected to begin in early 2007, which will see Kingspan’s registered contractors on site to erect the properties.

Crest Nicholson’s chief executive, Stephen Stone says: “Most important in this success has been our dedication to the ideals of building sustainability and environmental well-being in our plans for this development. The fact that overall, the SixtyK Consortium has won the right to develop three sites shows that we have successfully responded to the core challenges that the competition set the industry. Our innovations in design and manufacture have meant that in winning, we have exceeded its original brief and have set standards for the construction industry at a new higher level.”

Kingspan Century’s national sales manager for the TEK system, Jeff Tomlinson adds: “In addition to delivering cost efficiencies in the design, manufacture and construction process, central to the Consortium’s success was its strong focus on sustainability, renewable energy and cutting carbon emissions. To be awarded a third site has given a strong validation to our approach to environmentally sustainable housing design, supply and construction. The next step is to implement the designs in practice on the three sites.”

The proof of the pudding, as they say; now SixtyK must turn the vision into material reality to prove its design is not all stylish drawings and good intent.

Again, the onus will be on Kingspan’s TEK system and its impressive vital statistics. The SIPs are made from two sheets of oriented strand board, which is bonded during manufacture to a rigid urethane insulation core. This insulating element is CFC/HCFC-free so that it has a claimed zero potential for ozone depletion.

Thermally, the TEK system achieves low uvalues – Kingspan gives the example of 0.2W/m2.K – with no additional insulation required. To gain this value, the wall would be 223mm thick, the company says, compared to 390.5mm thick to achieve the same figure in a typical timber-frame wall, or 430mm for a full fill masonry cavity wall and insulating fillings. As a result, the TEK system gives greater floor space for the same size of structure.

TEK’s thermal performance is additionally enhanced by its airtight construction. The figure is as low as 0.08 air changes per hour at normal air pressures, or 0.91 air changes per hour at 50 Pa (approximately 1m3/hour/m2 at 50 Pa).

Additionally, the way the panels slot together means the insulation layer is not interrupted by repeating studwork, which therefore requires less cold bridging. Structurally, the TEK system can be used to build a three-storey structure, with living space in the loft. The panels are suitable for both walls – including load-bearing ones – floors and roofs. It can also be used as a roofing system in conjunction with masonry or timber-frame walls. The SIPs panels are also light enough to be used in locations where heavy construction isn’t suitable.

The system is recognised by the major building warranty providers such as HAPM, NHBC and Zurich Municipal. It also has BBA, IAB and Zulassung certification and it is fully EGAN compliant.

For constructors, the system helps to reduce congestion, noise and traffic pollution by contributing to reduced traffic to and from the site. This is because the panels are manufactured off-site to scheme designs, and can be delivered ‘flat packed’ en masse from one supplier. The technique also means there is less time spent on site building the houses and there is less site waste.

For the people who will live in the houses, it provides a more energy efficient living space that by lowering the need for energy demand will reduce bills and consume less fossil fuels. This was an important consideration in the Design for Manufacture competition, but SixtyK’s winning entries did not just rely on the sustainability credentials of the TEK system. Further eco-friendly features also played their part.

For example, the Rowan High School scheme includes combined heat and power (CHP) plant and mechanical ventilation and heat recovery (MVHR) installations. Photovoltaic cells will also make an energy efficient contribution to reduce carbon emissions. Each home will also feature rainwater harvesting and recycling systems, as well as make use of water saving toilets, taps, showers and other appliances. All three schemes are said to represent the delivery of sustainable houses that far exceed current building regulations, and are expected to remain in excess of regulatory requirements for some years to come.

Tomlinson adds: “The Consortium worked very closely to not only achieve cost efficiencies and innovative housing design for the development of the Rowan High School site, but also to deliver excellent sustainability credentials for the project. Our proposals were designed to minimise energy consumption and maximise the benefit to the homes from their natural environment – and it was this sustainable approach that pushed our bid into a winning position for the third time.”

Alan Shingler, a partner at Sheppard Robson, says: “Sustainability and cutting carbon emissions were a key driver in the SixtyK house design. By combining CHP, MVHR and renewable energy sources we will significantly cut carbon emissions. The conservation of water is another key focus for the design, with a drainage strategy to reduce demand for potable water, a distinctive landscape with swales and balancing ponds carving crescents into the urban landscape. A fully integrated sustainable approach to masterplanning and architecture has created a strong language which expresses innovation over mediocrity.”

Quite. The real test, of course, and so the real verdict, won’t be known for some time – not until people have taken residence and given them that ultimate “lived in” test.