Canada: bringing the forests into the city
Canada has the world's third-largest amount of forests after Russia and Brazil and just ahead of the USA. Yet in recent years it has produced only half as much timber and timber-based material as its southern neighbour. One reason is that Canada protects far larger areas of woodland than the USA. There is however, a clear need to catch up as regards making use of wood. In recent years many provincial governments have passed laws and launched initiatives to increase the use of timber also in the field of building. Here Canada's westernmost province British Columbia plays a pioneering role.
Canada and the northern states of the USA can look back on a long tradition of multi-storey timber building. At the end of the 19th century industrial and storage buildings up to nine storeys high were erected in the big North American cities using what is known as brick and beam construction. The external walls consist of solid brickwork, the internal load-bearing structure is a timber frame with heavy beams. This construction method allows maximum flexibility in dividing up the space and offers external fire protection and a representative appearance. A study made several years ago identified almost 20 brick and beam buildings more than five storeys high still in existence in Vancouver and nearly 40 in Toronto. The most impressive examples of this method include The Landing (1905) and the Leckie Building (1908) in Vancouver as well as Butler Square (1908) in Minneapolis. Most of these buildings have been converted into high-price office blocks.
It was only in 1941 that a national law was passed in Canada based on similar legislation in the USA. Timber building was restricted to seven storeys and later, in response to calls by the fire brigade, to just four storeys - the maximum height easily reachable by the fire engines of the time. But in any case concrete or steel frame buildings offered an economic advantage. Towards the end of the 20th century the emergence of new materials such as timber I-joists, cross laminated timber and glulam made multi-storey timber building economically attractive again and introduced a new dynamic. In 2009 the Provincial Government of British Columbia made two pioneering decisions: it permitted timber buildings up to six storeys and also passed the Wood First Act. This decrees that in all new buildings erected by the state timber is to be used as a structural material wherever technically and economically reasonable.
In 2013 the province of Québec also introduced the relaxation of fire protection legislation and in 2016 these laws were passed throughout the country.
Estimates from Initiative Wood Works show that in British Columbia alone more than 300 five and six-storey timber residential buildings have been erected since 2009 - mostly using timber frame construction. In recent years the universities and the state have also emerged as timber building clients: in 2012 the Earth Sciences Building of the University of British Columbia (UBC), a five-storey timber frame office, seminar and lab building, was completed in Vancouver to plans by Perkins + Will. Two years later Michael Green Architects erected the seven-storey Wood Innovation and Design Centre in Prince George entirely without concrete elements, using a bracing cross laminated timber core and an external timber frame construction. Computer assisted fire simulations and over-dimensioned building elements made it possible to expose the timber surfaces in the interior of the building.
Brock Commons student residence by Acton Ostry Architects on the campus of the University of British Columbia is also a timber frame building. Its 18 storeys make it the tallest timber building in the world so far. As it is outside the framework covered by the building regulations it required a special permit which involved fire protection expert reports and tests. In this case the structure was clad internally with plasterboard and a sprinkler system was fitted throughout the building.
The most recent height records have inspired other architects and investors. Shigeru Ban is currently designing the Terrace House, a 19-storey apartment building with a hybrid construction of steel, timber and concrete for a site in Vancouver's inner city. The planned height is 71 metres. For Toronto the Chinese-Austrian architecture office Penda together with the timber building consultants Tmber have conceived the 18-storey Toronto Tree Tower. This building's animated external volume is somewhat reminiscent of Moshe Safdie's "Habitat 67" in Montreal. In contrast to the earlier building the individual prefabricated spatial cells use cross laminated timber rather than concrete.
London: pioneer thanks to imported timber
Until the early modern period London was also a city built of timber, more precisely of oak. The half-timber buildings were generally made from native hardwood. Softwood (usually from the Baltic) only appeared in Great Britain in the 17th century, when the building of the fleet consumed increasing amounts of timber. However, the London Building Act of1667 had already severely restricted timber construction. In reaction to the disastrous conflagration a year earlier which destroyed 80 % of the city, it decreed wider streets and a new construction method: the external walls of all buildings were to be made of brick or stone and fire walls had to be continued above the roof.
From the 1920s onwards, starting from Sweden, modern timber frame construction began to establish itself in Great Britain, too. Initially confined to single-family houses, timber building experienced a small boom in the 1970s until in 1984 a critical TV report about poor quality and the danger of fire in timber houses caused the market to practically collapse. Nevertheless, fire safety restrictions were gradually eased in the following years: from 1988 four-storey timber buildings were permitted and from 1991 five-storey. At the end of the 1990s further relaxations were introduced as a result of tests carried out on a six-storey Building Research Establishment (BRE) test building. However, the discussion about fire safety continued, above all when a year later it was revealed that the BRE test had not been as successful as originally reported: hours after the fire appeared to have been extinguished the fire brigade had to return. Apparently, the timber construction in the wall cavities had continued to smoulder and ignited again some time later.
Today timber frame construction has a market share of around 15 % in single-family and apartment building in Britain, although there are sizable regional differences: in Scotland 75 % of all new residential buildings are erected of wood, in England only 9 %.
The timber construction industry hopes to defuse the fire safety discussion somewhat by the use of solid timber panels. The relatively poor urban district of Hackney in north-east London is playing a pioneering role here. At the instigation of the lobbyist Wood for Good (and with reference to British Columbia's Wood First Act) in 2012 the district administration wanted to pass a regulation requiring all new buildings to be built of wood - wherever economically reasonable. Objections to this proposal were soon raised by the cement and brick industry and some planners and even the UK Green Building Council also voiced opposition. Fearing the threat of legal action the administration backpedalled and since then has attempted to encourage timber construction in more informal ways - through information campaigns and discussions with investors who wish to build. The success is undeniable: Banyan Wharf by HawkinsBrown (2016, 50 dwelling units) and Dalston Lane by Waugh Thistleton Architects (2017, 121 dwelling units), the country's largest timber residential buildings to date were both erected in this district. Both financed by the housing company Regal Homes they are up to ten storeys high. While Dalston Lane was built entirely of cross laminated timber - apart from the ground floor but including the lift core, in Banyan Wharf steel beams were used to achieve greater ceiling spans that would facilitate later changes to the floor plans. With its larch cladding the new building by HawkinsBrown at least suggests that it is made of wood, whereas in most other contemporary timber buildings in London brick facing walls are the rule. This is due to local authority regulations but also because developers, eager to avoid controversies, attempt to integrate their new buildings in London's traditional appearance.
According to Andrew Waugh from Waugh Thistleton Architects the advantages of timber are not only ecological but also very practical. Thanks to prefabrication it allows lower dimensional tolerances, creates up to 80 % less building site traffic than a traditional in-situ concrete building, and can be erected more quickly. In the case of Dalston Lane the time saved in erecting the building shell was calculated as around 25 %. Time considerations also played the major role in the decision by the pay TV company Sky to have its new office and training building in west London erected almost entirely of timber. The general planner Arup required just a three month design and planning period. The construction is based on a glulam frame with a 6 × 8 metre grid, in which the cross laminated timber ceiling elements are hung. The facades use prefabricated timber panel elements. By over-dimensioning the timber structure the need for plasterboard cladding and a sprinkler system could be obviated.
A special aspect of London's timber building boom is that most of the material needed is imported from Austria and Scandinavia. As yet Great Britain has no production facilities for cross laminated timber. Timber supplies are also limited, as only 13 % of the land area is forested. Although timber production has almost tripled since the 1980s the country still imports four-fifths of the timber it needs. And this figure could well increase in the years to come, as a lot of woodland is being cleared in Great Britain with little reforestation which, where carried out, generally employs hardwoods, which are difficult to use in timber building. More than 40 % of British forests are not managed, as there are no incentives for the (mostly private) owners. The timber processing industry is therefore placing its hopes on Brexit: leaving the EU would allow the British government to pay direct subsidies to the forestry sector. At present the EU forbids the use of agricultural subsidies in this area.
Sweden: sleeping beauty awakens
Today the EU's most heavily forested country, in the 19th century Sweden passed the world's most restrictive fire protection legislation. After a number of disastrous city fires, in 1875 the construction of timber houses more than two-storeys high was completely forbidden. This only changed when Sweden joined the EU in 1994. Since then, instead of stipulating non-flammable materials in taller buildings, the fire protection regulations impose fire resistance requirements. However the Swedish building industry (which is dominated by a few large companies) has responded only sluggishly to this change. After the long prohibition there was a lack of design competence in the area of multi-storey timber building and of processing capacity for the material needed. The building firms began only gradually to develop the requisite construction systems (often in collaboration with the universities). In Sweden today timber building has a market share of 80 - 85 % in the area of single-family housing, in multi-storey housing the figure is (still) less than 10 %.
Timber building methods have enjoyed success above all in Växjö in southern Sweden. In 1996 this city (population 80,000) decided that it wished to be completely CO2-neutral by 2050. The country's first five-storey residential building had been erected in Växjö one year earlier, but was not followed by many others. A new dynamic emerged in 2005, above all in connection with the Välle Broar district in the south of Växjö. In 2009 four eight-storey apartment buildings built of cross laminated timber were erected in the city's new build district of Limnologen followed in 2010 by two further eight-storey passive house buildings in nearby Portvakten. The Vallen housing complex, completed in 2015, is nine storeys high and has a timber frame structure in which hollow box floor slabs are hung. In 2013 a decision by Växjö town council confirmed the direction taken: by 2020 25 % and by 2035 half of all new buildings erected by the state and communal housing companies are to be timber built.
Today several housing construction companies are also boosting timber construction in cities. In 2013 and 2014 in Sundbyberg on the periphery of Stockholm the firm Folkhem, together with the architecture practice Wingårdhs, erected two eight-storey apartment buildings in solid timber construction with a distinctive wood shingle cladding. The walls and roofs of the tall, narrow residential blocks are of cross laminated timber, the ribbed ceiling slabs are made from cross laminated timber and glulam.
Whereas previously Folkhem had used timber only for single-family houses, it now decided to concentrate exclusively on timber building, also for multi-storey housing. By 2030 the company intends to build 18 housing projects in and around Stockholm with a total of 6000 apartments, each project to be designed by a different architecture office. These plans include rather unassuming six-storey inner city buildings as well as the new build complex Loudden by Tham Videgård, which will consist of four 20-storey timber high-rise buildings offering a total of 220 apartments. Construction will start in 2025 at the earliest. In contrast two eight-storey buildings designed by Petra Gipp Arkitektur are already under construction in a new build district on the urban periphery. The client came up with an unusual PR campaign to market these buildings: these apartment blocks were the first buildings worldwide to receive an environmental product declaration. Usually this document is issued for individual products and provides detail of the ecological balance of the materials contained in the product and of the production processes.
Regulations and Laws
The experience In Hackney illustrates the difficulty of formulating legally watertight regulations that favour timber building and then pushing these through politically. In 2010 the French government had a similar experience with a decree imposing the use of 0.2 m³ of timber-based materials per square metre floor area in all new public buildings. In 2013 in response to legal action by the cement and concrete industry the French constitutional court declared the regulation anti-competitive and in 2015 the decree was annulled.
The municipal government of Helsinki met with greater success at local level. It is planned that the city will grow by more than a third by 2050. To facilitate this, following completion of a new industrial port in the east of the city in 2007, large areas of the old port around the inner city were cleared. For three of the new build areas Helsinki inserted clauses in the development plan explicitly requiring the use of timber construction. Here, too, the Finnish concrete industry lodged a complaint in 2015 but the highest administrative court declared the regulation legal.
On the site of a former barracks in the north-east of the city Munich is currently developing a model residential development with 500 dwelling units. Multi-storey buildings provide three-quarters of the total amount of housing space, with courtyard and row houses making up the remainder. Alongside energy-efficient construction timber building is also to be encouraged here. The project is interesting above all on account of the pragmatic assessment standard. In all new buildings a certain amount of renewable raw materials is to be used per square metre living space. For single-family houses the minimum requirement is 150 kg/m2, in the multi-storey housing only 50 kg/m2. While this means that the smaller houses on the site have to be built in timber frame or solid timber construction, in principle the figure for the apartment buildings could be achieved by a concrete building in which only the facades are made from timber elements. It seems, however, that the amount of wood used in building is considerably more than the required minimum. In the framework of a concept award system most of the sites were allocated to clients whose applications were successful partly due to their intensive use of timber.
Hidden revolution
The examples cited above show that the renaissance of urban timber building depends on numerous factors. New technical developments and a growing ecological awareness among the population are important motors. In addition the legal framework, above all in the area of fire protection, is most important. However, the decisive measures to be taken are at local level - with the clients and municipal administrations who must make timber building one of their concerns.
The keepers of the Holy Grail of architecture need not feel uneasy due to these new tendencies: in contrast to many other ecologically motivated innovations in building technology timber building does not threaten to radically alter the appearance of our cities and buildings. A tendency to use this construction material as a visible facade cladding is discernible only in Scandinavia.
