A woodland stroll to the gate

Warm light filters through a large oval skylight and creates an interplay of light and shade on the wooden flooring below. With trolley cases at their sides, travellers make their way to the waiting airplanes. The roof above them is made of regionally sourced Douglas fir and has a parametric design with an undulating, three-dimensional lattice structure that sweeps upwards towards the skylights. Living trees stretch out their branches underneath, partially surrounded by circular flower borders. There is no doubt that nature served as a key leitmotif for Portland International Airport (PDX) in the US state of Oregan, whose new extension opened in August 2024.

First US airport with wooden roof

According to Portland-based studio ZGF Architects, this is the first major airport in the US to be spanned by a timber roof. With the abundance of daylight in the terminals and the verdant planting, the design intends visitors to feel as though they are walking through woodland. After all, Oregon is well known for its ancient forests, and around half of this state in the Pacific Northwest is covered in forestland.

Collaboration between specialists for sustainable and biophilic design Terrapin Bright Green and the landscape architects at PLACE produced a holistic concept that fills every corner of the terminal with natural light and lush greenery. In total, over 5,000 plants and 72 trees now grow inside the airport terminal. Many of these are up to seven metres tall.

“The interior environment of the new main terminal is designed to increase passengers’ comfort and reduce the stress that many people experience while travelling,” according to ZGF. Aside from the good feeling created by the plants, they also serve as orientation and guidance throughout the building, accompanying passengers from security all the way to their departure gate.

Transformation with structural timber design

Even though airports are increasingly biophilic nowadays – for instance, Singapore’s Changi Airport has the world’s largest indoor waterfall landscape – Portland Airport has taken the concept a step further. In this case, the principle behind biophilia, which is human love of nature, has even influenced the construction method and sourcing of materials.

In line with this approach, timber was chosen as the building material for the airport extension, with the existing structures being transformed in the interests of an organic life cycle: “Instead of building a completely new terminal, much of the existing infrastructure, including the baggage handling system, was reused.”

Existing structures brought together beneath the wave

ZGF Architects, who were also responsible for the airport’s first extension back in the 1970s, presented a master plan for the whole terminal. This provided an overriding concept for a single, large unit that connects all nine buildings constructed over decades. The sculptured timber roof spans the entire terminal to unify the whole as a linking structure.

Beneath this enormous wave, the existing buildings are now consolidated with minimal ecological impact. “The decision to reuse much of the existing terminal, along with using wood and optimizing steel and concrete, enabled us to achieve a 70% reduction in the overall structural embodied carbon footprint when compared with building an entirely new terminal.”

The nine-acre roof consists entirely of Douglas fir timber and comprises 24m-long glulam beams, a CLT roof membrane and a lattice structure made of squared timber. It is supported by 34 Y-shaped columns equipped with seismic isolation bearings to enable the roof structure to move sideways as much as 60 centimetres during an earthquake.

Forest to frame 

When it came to sourcing the wood, they left the well-trodden path of traditional methods. Instead, they introduced a new principle that corresponds to the farm-to-table concept familiar from the food sector. Called “Forest to frame”, it takes a similar approach to establishing a value chain which also supports small businesses and forestry operations instead of awarding a major commission to the big players in the timber construction industry.

The first step was to find over 6,000 cubic metres of wood to build the whole structure. Right at the very beginning, the team posed the question: “Can we source all this wood in a way that is better for the land and better for our local communities?” Ultimately, they decided to source the entire timber requirements for the huge wooden roof from forests in the Pacific Northwest, within a 300-mile radius of the airport (approx. 480 kilometres).

“It was essential to the team and client to target and celebrate the underrepresented parts of the supply chain. This meant going the extra mile to make sure the project sourced its wood from small mills, small family forests, non-profits, and tribal nations.”

Sourcing model for the common good

Therefore, a large proportion of the wood used to build Portland Airport can be traced back to the forests and engineering works where it was harvested and processed. This transparent approach boosts diversity among regional businesses and benefits the community. “It is the first time that this has been implemented on such a scale in the US,” explain the architects at ZGF. Their hope is that this sourcing model will prove popular elsewhere in future.

With its large-span, hybrid timber construction, Portland is ahead of a similar project in Switzerland. The extension for Zurich Airport will also use wood as the preferred building material for a spectacular timber spatial frame. In Oregan, by preserving the existing buildings and democratizing the supply chain, the project is setting new standards for the construction industry.

Text: Gertraud Gerst
Translation: Rosemary Bridger-Lippe
Photos: Ema Peter Photography