Berkeley Homes’ 147-unit Holborough Valley development is a confection of pastel shades – think Trebor Refreshers – that lift the spirits even on the dullest day. But the site is more than just eye candy. Behind the colourful façade there’s a wealth of state-of-the-art timber engineering and tons of timber.
The use of timber frame for such a grand development (the 60-acre site will see 1,000 units over the next five or six years) marks new territory for the Berkeley Group in this neck of the woods.
“Berkeley Homes has used timber frame in certain parts of the group, but this is the first venture into timber frame in our region,” said south-east London commercial director Nigel Tompsett. “It’s been widely recognised that timber frame has benefits, not least of which is speed of construction and we were looking at the New England-style of development here and felt it was appropriate to dip our toe into that market.”
The last 18 months have undoubtedly been “quite a learning curve” for the developer, but they’ve also been rewarding. “We’re very pleased with the product we’ve got here and with what we’ve achieved collectively,” said Tompsett. “There has been a very collaborative approach to this new method of construction.”
The collaboration he refers to is with Berkeley’s main contracted supplier for Holborough Valley, BSW Alouette. The latter is a joint venture between Ramsgate-based BSW Timber Systems Ltd (part of the BSW Group sawmilling giant) and Canadian Super E home manufacturer Alouette International Housing. The two companies started working on the project as separate entities but formalised their relationship in April.
The Holborough Valley development has been a seminal experience all round. While Berkeley Homes has benefited enormously from its contractor’s expertise, BSW Alouette’s fortunes have been transformed. “This contract is worth £3.3m, so the project has really boosted our profile,” said its managing director, Norman Gore.
BSW Alouette’s remit was to design and supply all the timber frame housing for Phase 1 of the development. While the roof and floor systems have all been manufactured at the Ramsgate base, the closed panel walls, complete á
Ü with insulation, vapour barrier, breather membrane, windows and service void counter battens, have been manufactured at Alouette’s factory in Québec.
In addition, the company has been responsible for co-ordinating the design of all the exterior finishes, including the fire-treated Cape Cod cladding, with Berkeley’s technical department and project architects and engineers. It has also supplied fascias, soffits and trims and, in association with subcontractors, supplied stairs, balustrading and landings, balconies and porch assemblies.
All the elements are designed and manufactured in accordance with Super E requirements or Building Regulations, whichever is the greater (Super E satisfies the requirements of the revised Building Regulations Parts F & L).
Bolstering BSW Alouette’s efforts is specialist timber engineering consultant TimberSolve Ltd which oversees the whole design and ensures compliance with UK Building Regulations and British Standards.
TimberSolve came into its own when the main balconies proved tricky. “The challenge was their durability,” said director Luke Whale. “NHBC dictates that timber can’t be used for exterior structural balconies, but after some cajoling it provided the requirements that would allow us to work out a solution.”
The NHBC requirement was for a lifespan of 60 years without treatment or preservative. A hardwood was the obvious solution but it also needed to be sustainable and not too expensive. Laminated American white oak proved itself to be the most suitable and this has been used for all the main structural members. The posts are generally 160x160mm with
the ground floor posts bulked out using laminated softwood.
After ratification by BRE, NHBC gave the balconies the all clear and, said Whale, there’s no reason to suppose that future housing shouldn’t incorporate similar designs. In a few months time the durability issue may be further put to bed when BSW will be able to throw Accoya modified timber into the mix.
Accoya is produced using a non-toxic acetylation process that effectively converts sustainably grown softwoods and non-durable hardwoods into a new wood species. The technology was developed by Titan Wood and BSW Timber is its exclusive supplier in the UK and Ireland. Research between the two and with specialist finishes manufacturer Akzo Nobel Sikkens has resulted in a product with impressively low maintenance requirements. Soffits and fascias are obvious candidates for use of Accoya and it may be considered for structural elements such as balconies.
While full-scale commercial use of the timber modification technology is still a few months off, Super E technology is already winning friends and influencing people. Alouette is the largest manufacturer of Super E houses in the world and in 2001 was responsible for the first house using the system in the UK – a Sunley Homes development in King’s Hill, in Kent.
Since that time, Super E, which BSW Alouette describes as “a technical standard based on the ‘house-as-a-system’ philosophy of design and construction” has made inroads into the construction world’s psyche as building physics have become more important.
Jeff Culp, general manager of the Super E programme, has certainly noticed a growing awareness and acceptance of the system. Speaking at this year’s Interbuild he noted that, perhaps as a result of the increasing focus on Part L, visitors to the show were “much more clued-up about Super E than á Ü two years ago and much more accepting of timber frame”.
The beating heart of the Super E home is the heat recovery ventilator (HRV) which ensures an even distribution of fresh air and controls humidity levels. “There is only a 0.5O variance in temperature throughout the house,” said BSW Alouette sales director Martin Stebenne, “and the HRV also eliminates cooking smells and condensation from kitchens and bathrooms from the rest of the unit.”
Apparently one of the issues Berkeley Homes had been concerned about when heading down the timber frame route was transfer of sound. However, in the event, the units are performing “20% better” than Building Regulations demands on sound transfer through windows and party walls. The floor systems, which are based on Eleco’s open web Eco-joist, are also outperforming Building Regulations by “at least 5 decibels on average”, according to Luke Whale.
Airtightness is crucial to the Super E system’s goal of better acoustic performance, ventilation and thermal performance and, as part of BSW Alouette’s package of services, all site personnel were trained on its principles.
“They need to understand the product and how it works,” said Nigel Tompsett. “That applies particularly to the carpenters, but also to the following trades. They have got to be thinking airtightness the whole time. You can’t have your carpenter understanding the whole philosophy and then the plumber coming along and putting holes in. He also has to understand that everything he does has got be sealed when it passes through the membrane.”
“Before we started work on the site we ran a day’s seminar with all the contractors,” continued Martin Stebenne. “We asked them all how many holes they needed to make in the membrane and where and then we worked with them to find a way to seal them. That way each of them had a solution in hand to carry out their work.”
To qualify for the Super E certification, each unit must pass a final depressurisation test, conducted by a third party. Berkeley ensures it’s on the right track by testing airtightness at two additional stages – the first after the frame is erected to ensure membranes have been sufficiently lapped and sealed, and the second after the services have been installed, to ensure any punctures have been sealed.
The test is carried out by using a blower door, which depressurises the house and then measures the amount of air that needs to be sucked out of the building to keep it depressurised. The leakier the house, the more air will be sucked in from outside as a result. While a typical new house may have an air leakage rate of around 10 air changes per hour, a Super E house achieves 1.5 changes per hour.
The science – and indeed the build method – may not interest the majority of Holborough Valley’s prospective residents, but energy efficiency, air quality and noise control certainly do. These are also key considerations for the social housing element that accounts for around 25% of each phase of the development. “Not only are these houses and apartments cheaper to run and heat, but they have a very particular ambience,” said Tompsett. “The quietness and air quality makes them a very nice environment to live in.”
With half a dozen units still to be completed in Phase 1, Berkeley Homes is currently considering its verdict on the rest of the site, so whether more Super E and, indeed, timber frame homes follow in Phase 2 onwards remains to be seen. But it’s fair to say that the experience of both has so far been salutary.
“We are over 50% sold, so we’re very pleased with sales here,” said Tompsett. “It’s a very good position to be in.”
Of course, the Berkeley name, the location, the price and aesthetics of the Holborough Valley development are all responsible for the sales success, but timber frame has undoubtedly played its part.
“We’re very much behind this product and would like to use it in the future,” said Tompsett. “It’s been a good experience.”
