Imagine a house that doesn’t have just one life, but several. 

Where walls, floors, and structural elements don’t end up as waste when the building is demolished - but instead become part of new constructions.

This is the core of Jiayi Kayee Li’s PhD. 

She works with timber modules of varying sizes that can be assembled as needed – from single-family homes to high-rises. 

When a building is no longer in use, the modules can be disassembled and reused in new constructions – a bit like building with Lego bricks.

“We need to move away from the idea that buildings are something we erect, demolish, and throw away,” says Jiayi Kayee Li.

Instead, we can imagine flexible cities where buildings can be moved or modified according to demand.

“You can reuse the wooden floor in a new building. This way, material that would otherwise become waste is kept in use,” she explains.

Jiayi Kayee Li has analyzed 60 existing modular wooden buildings to understand which design principles work best in the current practice. 

She has also conducted her own experiments to study how to recycle timber that would otherwise have been discarded to create a load-bearing floor. 

The positive results indicate that these reclaimed timber floorboards can conserve resources while ensuring structural safety.

“This is important knowledge. The more circular materials we use – like reclaimed timber – the more we reduce construction waste and lower the carbon footprint,” she emphasizes.

Construction Pressures on Resources

Her research addresses one of the construction industry’s greatest challenges. 

Globally, construction is among the most resource-intensive sectors, and construction and demolition waste accounts for roughly 40% of Denmark’s total waste. 

At the same time, much of the existing building stock is approaching the end of its intended service life, meaning that massive amounts of buildings will soon require renovation or demolition. 

This results in large volumes of waste and further pressure on natural resources.

Jiayi Kayee Li’s work points to an alternative approach and a potential solution: using materials that can circulate rather than become waste.

“Instead of repeating the old story of build – use – demolish – discard, timber modules can make buildings circular,” she says.

Timber as a Key Material

The choice of timber is deliberate. It is renewable, stores carbon and weighs less than steel or concrete.

 While structural frameworks are traditionally made of steel and concrete, Jiayi Kayee Li demonstrates that timber can now also serve as a load-bearing element in mid- and high-rise buildings.

“Of course, you wouldn’t build Lighthouse with timber as the only structural element, but even high-rise timber buildings like Mindet incorporate a timber-concrete composite structure,” she explains. 

Timber is light compared to concrete, but still strong. Moreover, its fire resistance is far better than one might imagine., she emphasises. 

In many European countries, timber is treated on par with steel and concrete even in tall buildings. The difference depends on local regulations and how mature the industry is in each region.

Less Waste, Faster Construction

Globally, timber buildings built with reclaimed timber remain relatively uncommon. 

This study aims to develop proactive design and technical solutions. 

Amid the growing uptake of modern timber construction, there is a stronger imperative to anticipate future renovation and demolition challenges at an early stage, much like early 20th-century concrete buildings, which now face widespread renovation and demolition issues after around six decades in service.

However, the modular construction method offers numerous advantages, that Jiayi Kayee Li hopes will gain wider recognition.

For example, modules are prefabricated in factories and assembled on-site, making the process more precise and reducing material waste by up to 90%. 

Construction times can also be shortened by 30–50%, saving time, money, and labor.

“These are economic and practical gains – in addition to the environmental benefits,” she emphasised.

Concerns have been raised that reclaimed timber modules could lose strength after reuse. 

Jiayi Kayee Li’s research shows this is not the case. By comparing experimental test results with simulation data, she can predict how products perform when incorporated into new buildings. 

This ensures that flexibility and safety are preserved: buildings can be modified or extended without compromising structural performance.

A First Step Toward Circular Cities

Her research focuses on integrating digital construction technologies with modern building methods, with a primary emphasis on optimising designs from the perspective of structural performance.

It does not yet include full lifecycle assessments or aspects such as fire and moisture but lays the groundwork for future development.

The next steps include exploring further possibilities for using reclaimed timber in construction and focusing on modular products for refurbishment and renovation.

Jiayi Kayee Li demonstrates that it is technically feasible to combine flexible buildings with material reuse – with significant benefits. 

The goal is buildings that can be constructed, adapted, and reused again and again.

“Where materials don’t become waste but remain a resource. Ultimately, buildings that are not only less harmful to the climate, but regenerative,” she concludes.

Professor Lars Vabbersgaard Andersen supervised the PhD project.