Schooled in timber - using wood for the construction of schools
What benefits can be gained by using wood for the construction of schools and what are the key issues to consider? Gary Price investigates.
Public spending cuts have sidelined the UK Government’s plan to rebuild or refurbish schools in England. Scrapping the Building Schools for the Future programme will have a huge effect on construction and manufacturing firms.
The scale and speed of the initiative implied that the UK was entering in to a ‘school-building boom’. ‘The scheme was designed to deliver a large number of schools quickly, creating buildings for individual sites and briefs,’ says Michael Ankers, Chief Executive of the UK’s Construction Products Association. ‘Now many schools will fall into disrepair.’
The UK has faced problems like this before. After the Second World War, the Government pledged to build new houses and schools, but had no money to do so. However, local governments across the country found ways to deliver buildings quickly and cheaply, and the 1950s ended with a tower block building and social housing boom.
Rebuilding bombed-out landscapes in steel and aggregates, however, led to criticism regarding the bleakness of the estates and the ‘concrete jungle’ aesthetic. This could perhaps explain why many architects and town planners are now so keen to use timber structures for their building projects. A seminar at the Building Centre in London, UK, earlier this year demonstrated how the education building programme could have been fulfilled using timber frames – a material not as prominent as steel and concrete in school design.
Presenting case studies of current and recently completed projects, the event, Schools – Meeting the Brief with Wood, explored advances in timber construction and took a look at some of the issues and constraints in the education sector.
‘The versatility and enduring aesthetic appeal of wood has never been stronger than today,’ claimed Frank Werling, Building Systems Technical Manager at Finnforest, based in Grangemouth, UK. ‘Structural timber can now achieve wider spans, and it can be bent and curved using customised tools so there are no longer limitations to forms. Advanced digital computer aided design enables precision in timber detailing and facilitates automated processes between consultation, manufacture and installation.’
Werling is helping to design and deliver The Hub at York University, UK, which will house a theatre, science laboratories and classrooms.
‘The thermal mass aspects of timber may not be as good as concrete or stone, however, too much thermal mass is not a good thing,’ he adds. ‘The key is achieving the right balance between comfort and energy savings. Natural ventilation can be achieved in the summer, and, in winter, spring and autumn, mechanical heat recovery ventilation can be used as needed.’
Werling went on to say that timber design is not expensive if all aspects of engineering are considered from the outset. ‘During timber construction it is crucial to understand the difference between detailing in timber and steel,’ he said. ‘Because timber moves as a result of moisture, all joinery details need to be worked out beforehand.’
Most structural timber used in UK schools so far has been sourced from Finland, Austria or Germany, because the conditions are perfect for growing species for these applications, continued Werling. To date, UK timber is used primarily for joinery.
Vision for the future
But what benefit is wood bringing to end-users and what issues should contractors be aware of?
‘Schools should provide an inspirational environment for both teachers and pupils,’ says Karlheinz Weiss, Managing Director of KLH UK, headquartered in London.
With this in mind, the designers of timberbased Lauriston Primary School in London, UK, have focused on the effective use of sound to create ‘cohesive, innovative learning environments’. For acoustic reverberation, the school has angular forms wherever possible, reflecting sounds from the surfaces and helping to overcome the inverse square law drop-off.
‘Classrooms with poor acoustics can result in children with normal hearing being unable to wood focus 21 issue 2 2010 Feature make out what is being said in class,’ explains Weiss. ‘While adults will guess at missing words, children find it much harder to fill in the gaps and their educational development can suffer.’
Though Weiss says that the construction of the school was relatively straightforward, as most interior and exterior panels were fabricated offsite, contractors still faced some challenges.
‘You can make certain assumptions about steel that we could not with timber,’ says Weiss. ‘For example, we know that steel will not swell in certain weather conditions, and how it interacts with the rest of a building.’
Although a structural engineer generated the details of timber interfaces, KLH architects had to understand how they worked because they were responsible for signing off the drawings. ‘It has been a learning curve, but a very interesting exercise,’ Weiss adds.
Specifying wood also has aesthetic benefits, according to Tony Davies, Senior Project Coordinator at PGA Architects, who says that the material enables the introduction of ‘architectural niceties’ within a building.
The firm, based in Johannesburg, South Africa, helped to deliver the Princess Royal Sports Arena in Boston, UK, in 2005. ‘The wooden rotunda that forms the reception area would have been too expensive to construct in steel because the curves would have been too difficult to reproduce,’ says Davies.
The natural appearance of the interior is the result of the decision not to stain the ply panels. ‘We like the way the appearance of the panels varies naturally,’ says Davies. He is less pleased, however, with the rough finish, which was caused by the need for a high level of fire protection. A thick intumescent coating was required to achieve a fire rating of zero, which meant the smooth natural texture of the ply was lost.
Baptism of fire
Fire is a real safety concern and a London Assembly investigation into timber-framed buildings was launched in 2009 after several large fires in the capital.
Lachlan McDonald, a structural engineer at Ellis and Moore, a consultancy based in London, explains, ‘When timber-framed buildings catch fire the actual structure burns. That is the last thing you want in a multistorey building [like a school] and it often leads to total collapse.’
Brian Coleman, Chairman of the London Fire Authority, says he has always been a stern critic of large timber-framed buildings. ‘Sadly, these days developers looking to build things quicker and cheaper have resorted to timber.’
In February of this year, however, the UK Timber Frame Association launched the Sitesafe initiative to minimise the risk of fire on timber frame construction sites. It has been backed by the Chief Fire Officers Association and relies on collaborative working in the construction supply chain to reduce the risk of fire on timber frame construction sites.
McDonald notes that, once erected, cladding timber panels with plasterboard will help contain the spread of fire. This, he says, is a relatively low cost and common practice.
‘When used as a component in fire barriers, plasterboard is a passive fire protection item. In its natural state, gypsum contains the water of crystallisation bound in the form of hydrates. When exposed to heat or fire, this water is vaporised, retarding heat transfer.’
Felling to selling
It seems there is a growing appetite among architects and developers to incorporate timber into their new school designs. But with the current global economic situation making costs even higher on the agenda than usual, can this material provide any respite to firms struggling to meet their project budgets?
‘Timber prices have fluctuated widely for the last two years,’ comments Robin Lancashire, a Timber Consultant at Trada Technology in High Wycombe, UK. ‘Prices were rising continuously due to demand, the cost of oil and in land transportation charges, and a scarcity of good logs.
‘Over the long-term, however, the cost of wood is relatively more stable than some other materials such as steel.’
The continued demand for wood-based products is also ensuring that any shortterm fluctuations remain relatively small. ‘Just like every other commodity in the world, wood prices have dipped over the past six months or so, although not at the same rate as steel,’ Lancashire continues. ‘The need for wood is still there, even if there is no real construction boom.’
It remains to be seen whether renewed interest in timber will create school buildings that can compete in the long run with the brick and concrete structures still dotted about the UK more than 50 to 100 years after they were built. Moreover, the impact of terminating the BSF programme is as yet unclear.