Engineered wood is fast becoming a popular structural material for tall timber buildings.
A series of multi-storey wooden projects are rising across the globe, and now the White House has again demonstrated its strong government support through a competition initiative.
The United States Department of Architecture (USDA) has formally launched a Tall Building Competition in support of sustainable forestry and to demonstrate the viability of building with wood.
The competition follows a funding announcement earlier this year by the White House Rural Council in collaboration with the USDA, committing to a climate-driven intimate that would see architects, builders and engineers trained in the benefits of wood as a structural material.
“Wood may be one of the oldest building materials, but is now also one of the most advanced,” Agriculture Secretary Tom Vilsack said earlier this year.
With a project prize of US$2 million, the competition is supported by the Softwood Lumber Board and Binational Softwood Lumber Council. It aims to attract US developers, institutions, organisations and design teams willing to undertake an alternative solution approach to designing and building taller wood structures.
The competition’s objective is to identify builders with projects in the concept-, schematic- or design-development state in the US that can safely demonstrate the use of wood in tall buildings.
“There is a breadth of wood-related building science, design and construction that’s underway internationally,” said SLB board chair Marc Brinkmeyer. “In recent years we’ve seen a number of buildings over seven stories constructed around the world, including the 10-story Forte building in Melbourne, Australia and the 14-story Treet building in Bergen, Norway. The opportunity to learn from what’s been done elsewhere, and build on it here in the US, is very exciting for our industry, our employees and communities…Wood truly is an optimal choice for the environment and economy.”
Brinkmeyer’s comments echo those of tall timber building advocates across the globe, such as architect Michael Green.
Green has created timber products and regularly demonstrates his support of high-rise timber buildings. He was featured in a video series with the Washington Forest Protection Association, predicting a revolution in wooden buildings that could help environmentally reshape cities.
“A century ago, it was a competition between different cities and developers to build skyscrapers and they really shaped the skylines of the world – I think we’re in that same phase, eventually,” he said.
In the series, Green speaks from his firm’s office – a 105-year-old, seven-storey wooden building in British Columbia, Canada. He believes architects need to consider timber as a new and fundamental structural material, describing doubt as an educational barrier rather than an engineering one.
In touting timber buildings, Brinkmeyer mentioned the Treet project, which will rise 49 metres and span 14 storeys. According to Norwegian paper The Local, the project will combine prefabrication with utilising wood in a tall building.
“The project is expected to sequester approximately 1,000 metric tons of CO2 in its wood construction, which unlike some other projects, includes the core. It will be clad in glass and steel to protect the wood from Bergen’s damp climate,” the paper reported.
British Columbia is a hot spot for tall wooden buildings.
Just last month, North America’s tallest all-wood modern building designed by Green’s firm opened in Prince George, BC The $25 million Wood Innovation and Design Centre (WIDC) was built to LEED Gold status and spans 50,000 square feet. Constructed by PCL Constructers Westcoast using 1,700 cubic metres of wood, the only concrete is in the raft slab foundation and a small concrete topping at the penthouse level for the mechanical equipment.
“Wood generally has been part of construction but not the entire construction,” PCL project manager Chad Kaldal said. “Every time you do something for the first time, there are a lot of unknowns but the important lessons learned from this building will help improve wood construction going forward so we can expand the use of it and catch up to places like Europe.”
The WIDC is almost exclusively made up of engineered wood components including glulam columns and beams; cross-laminated timber (CLT) for the floor assemblies and core vertical panels while laminated veneer lumber (LVL) was used for highly visible areas such as the stairs and canopies.
Despite the positive projects in the pipeline for tall wooden buildings, or “woodscrapers” as they are commonly known, resistance still remains in the industry. Most skyscrapers are still made from concrete, steel or glass and “greened” through the application of environmental technology, cooling facades and foliage.
Timber is gaining traction as a renewable building material, however, due it large part to its carbon sequestering abilities.
In a TED talk last year, Green reported that steel use is responsible for about three per cent of man’s greenhouse gas emissions while concrete is responsible for over five per cent.
He added that a typical 20-storey concrete building emits 1,215 tonnes of carbon dioxide, while wood sequesters 3,150 tonnes of the gas for a net difference of 4,356 tonnes – the equivalent of removing approximately 900 cars of the road each year.
In a recent blog post, Narangba Timbers in Queensland described timber as having “inherent advantages”.
“To produce a cubic metre of timber, 15kg of carbon is released into the environment, but that timber stores 250kg of carbon. That means every cubic metre of timber removes 235 kg of carbon from the environment,” the timber supplier wrote.
The company suggested that, in the context of tall buildings, a cubic metre of steel releases 5,320 kilograms of carbon into the environment, a cubic metre of concrete releases 120 kilograms of carbon into the environment and a cubic metre of aluminium releases a whopping 22,000 kilograms of carbon into the environment.
Despite its obvious benefits, some still have fire concerns where timber is concerned. This need not be the case, particuarly if it is a larger building, according to Green.
The architect describes tall wooden buildings as “incredibly safe” and says concerns over fire suppression are overstated.
“Even in the forest, if a fire goes through, the big trees stay standing, they char on the outside, the inside remains alive and those trees very often continue to grow for centuries especially here in the Pacific north west,” he said.
A 2013 study by Arup, Fire Safety Challenges of Tall Wood, found that fire in timber buildings under construction (particularly light timber frame buildings) had a higher potential of a complete burnout and threat to adjacent structures due to fires occurring “prior to the installation of gypsum board fire protection or automatic sprinkler protection.”
However, as Green said, the heavier, the safer.
“Fire incidents in heavy timber buildings tend to result in smaller fires, as large timber sections have an inherent fire resistance,” he said. “Additionally, charring in the heavy timber member will delay the onset of combust providing greater time for fire fighter intervention”.
While Arup did find complete burnout examples in completed buildings, the fire spread was generally restricted to the room of origin.
So while the last 100 years have seen skylines rise in grey tones of concrete and steel, the project pipeline looks a little more honey and caramel coloured as wood begins to take centre stage once again.