OUT OF THE WOODS: modular wooden skyscrapers

11 July 2018

Penda is planning a modular wooden skyscraper for Toronto that could provide a more sustainable model for high-density city living. Frances Marcellin talks to Chris Precht, a partner at the firm, about a material hitting new heights.

While much of the discussion surrounding the part timber may play in creating sustainable cities has recently surrounded the headline-friendly notion of wooden skyscrapers, there is growing excitement regarding how the material, and more specifically cross-laminated timber (CLT), might be able to help increase urban density more generally. Five times lighter than concrete, boasting impressive tensile strength and impeccable environmental credentials, more outlandish proponents are even predicting the return of a settlement type we assumed was consigned to history: the wooden city.

When start-up architectural firm Penda won Architizer’s A+ Award in 2016 for ‘Emerging Firm of the Year’ the team was already developing the ‘Tree Tower Toronto’. Sustainable, efficient to construct and designed with city dwellers’ health in mind, Penda hopes this wooden, 18-storey tower will act as a catalyst for future high-rise buildings.

Quite naturally

Penda has partnered with CLT consultants Tmber to design and deliver this modular, 62m-high building. It offers a 4,500m² residential area and 550m² of public space, which includes a cafe, a children’s day-care centre and community workshop areas.

“Our cities are an assembly of steel, concrete and glass,” says Chris Precht, partner at Penda. “The warm, natural appearance of wood and the plants growing on its facade bring the building to life and that could be a model for environmentally friendly developments and sustainable extensions of our urban landscape.”

By building with wood, Penda’s goal is to set a successful residential building precedent that would reduce pollution caused by the construction industry.

“The construction industry is using almost half of all energy created on our globe, and we are a big contributor to the pollution of our environment,” says Precht. “Buildings are using up sites and resources of our surroundings and I believe buildings can be and do more than that.”

Today, more than 80% of people living in urban areas are exposed to air quality levels that exceed the World Health Organization (WHO) limits. Reports show that 30% of global greenhouse gas emissions are attributable to buildings and, currently, the construction industry in the UK creates 32% of landfill waste and as much as 50% in the US. In Canada, waste from construction, renovation and demolition has increased by over 30% in 2000–10.

“As architects, we shouldn’t only think about how to make our buildings more beautiful or more efficient, but we need to design healthier buildings for vital cities,” says Precht. “Creating more public spaces in them, producing energy or growing food for the neighbourhood.”

With a long tradition of wood construction for housing and a also being pioneering country for vertical wooden structures, Canada was the ideal location to begin developing a modular wooden highrise. In order to promote sustainable developments, the government in Canada awards credits of up to 20% in funding for buildings that exceed carbon footprint standards.

Canada is also a country with a world-first in prefabricated modular construction, and in 1967 it opened Moshe Safdie’s Habitat 67 in Montreal, Quebec. Its intention was to be a new model for inner -city living – instead of small flats in soaring high-rise blocks, it provided compact house-like accommodation that made sure to include small gardens.

As architects, we shouldn’t only think about how to make our buildings more beautiful or more efficient, but we need to design healthier buildings for vital cities.

Ab prefab

Habitat 67 was constructed from 354 prefabricated modules, which were stacked and linked by steel cables. A project that never reached its potential – the overall size was reduced by the government and was thus more expensive than planned – it presented an environmentally aware method to consider and produce compact living in specifically urban environments.

Buildings are using up sites and resources of our surroundings and I believe buildings can be and do more than that.

“Inspired by Habitat 67, the Tree Tower is using a modular building process, where prefabricated and pre-cut CLT panels are assembled to modules off-site at an indoor facility,” says Precht, adding that while building modular is nothing new these days, building modular with individuality and variety takes it to above and beyond.

“After the work on-site, with foundation, ground floor and a base-core done, all modules including fixtures and finishes are delivered to the site and craned into place,” he adds. “During the process of stacking the modules, the timber clad facade panels are installed and sealed.” Precht explains that by going fully modular and prefab, the process is faster, less noisy, reduces waste and ultimately allows a high degree of quality control.

“The structure of the building is mainly massive timber panels with a hybrid of CLT, concrete and steel elements, where needed, and can be seen as a prominent statement to use engineered wood products in vertical structures,” he adds.

Yet as inspiring as Safdie’s Habitat 67 is, the building later allegedly encountered issues with damp after water crept into the concrete in specific places across the building as a whole. However, Precht explains that the extensive processes the wood goes through means it would be protected from any similiar issues from occurring.

“What I love most about building with solid wood panels is that, on one hand, wood is a natural and low-tech material, but on the other hand, the process of engineering cross-laminated timber panels is highly technological and mechanical,” he says. “Due to a sophisticated assembly line and CNC-milling, all details of the parts and eventual connection of the materials is precise.”

Precht adds: “Despite a precise building process and engineered details, it’s absolutely crucial to protect the wood from water. To prepare for the elements, once the prefabricated elements are put into place, the building is treated as any other conventional construction. A layer of water-protection is applied onto the building and a waterproofed cladding mounted on the building’s facade.”

While Precht says that Penda is currently in the “schmerzlich phase” of the project – meaning ‘painful’ – and the company is trying to get started on the approval process in 2018.

“We hope the building could be an example of a more ecological future in our cities,” he says. “To misuse a John F Kennedy quote – the question shouldn’t be what a city can do for a building, but what a building can do for a city. With this in mind, I hope the ‘Toronto Tree Tower’ sets a standard.”

The Tree Tower Toronto, Penda.
Interior of the Tree Tower Toronto, Penda.
The Tree Tower Toronto, Penda.
Chris Precht (left) and Dayong Sun (right), Penda.

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