Sustainable construction

What’s best for the climate—renovation or demolition?

Is it better for the climate to demolish poorly insulated homes in favor of more energy-efficient new construction? No, says a DTU researcher who has analyzed 120,000 demolitions and found three reasons why buildings are demolished.

Originally, the plan was for Høje Taastrup's former town hall to be demolished to build housing, but instead the developer chose to preserve the building and convert it into apartments and build houses on top. Photo: Visualization by Lendager Arkitekter

Wednesday 02 April 2025

Sole Bugge Møller

Høje Taastrup’s former town hall stood empty and ready for demolition after the municipality had built a new town hall. Instead, the site was to be used for new townhouses and apartments. But the housing developer that had taken over the site suddenly saw potential in the former town hall that made them change their plans.

“Walking around the building, we realized that it’s built with good materials and flexibility has been thought into the building. So the architect asked: 'Why tear this down?' Ultimately, we agreed that we couldn’t justify having a sustainability agenda while demolishing such a building,” says René Brandt, CEO of Ikano Bolig.

Instead, they will convert the town hall into 200 apartments, and according to Ikano Bolig’s own calculations, this will save approximately 7,500 tonnes of CO₂ and 560 truckloads of construction waste.

Demolishing is the easy way out

The most sustainable square metres are the ones we don’t build. Building materials account for up to 80% of CO₂ emissions from new construction over the lifetime of a building. Therefore, we need to reduce material consumption by, for example, renovating and reusing our existing buildings rather than demolishing and building new ones. This is the opinion of Rune Andersen, Assistant Professor at DTU Sustain and a circular construction researcher who has mapped 120,000 demolitions in Denmark.

“Høje Taastrup town hall is a good example of how you can achieve extremely high CO₂ savings by not demolishing,” he says.

And it’s not just builders, but also private individuals who need to get better at renovating, as 18% of all demolished square metres are single-family homes.

“In the past, people would add on if they needed more space, but now it’s more common to tear down and build new. It’s easy because you get a quote from a company that takes care of the demolition and builds a new house exactly as you want it, whereas if you build an extension, you have to do all the planning yourself and get an architect and tradesmen involved,” says Rune Andersen.

Facts

Increased risk of demolition

Three factors increase the risk of a building being demolished rather than renovated, according to Rune Andersen's research:

Ceiling height
Low ceilings leave no room for technical installations when converting a building from, e.g., housing to offices.

Load-bearing structures
Load-bearing interior walls make it more difficult to transform the building because room dimensions are more fixed.

It is an industrial building
Two thirds of all demolished square metres are industrial buildings in agriculture, offices, manufacturing, and service industries. This is partly because they are more difficult to transform for other purposes, and partly because they may be located in less attractive locations in relation to converting them to housing.

Conservation is best

Construction companies often argue that it’s better for the climate to demolish older homes because they have poor energy utilization, whereas a newly built house requires far less energy to heat.

But according to Rune Andersen, this is far from always the case. He has helped calculate the climate impact of energy renovating a 1970s detached house by, for example, replacing windows and insulating external walls, and compared it to constructing a new building. The conclusion is that the renovation has half the climate impact of a newly built brick house.

“Of course, it depends on how extensive a renovation or remodelling is needed, but it’s almost always worth preserving rather than demolishing from a climate perspective,” says Rune Andersen.

Climate preservation value

But sometimes it’s cheaper to tear down and build new rather than renovate, both for individuals and developers. When you demolish a building, you don’t pay property tax while you’re building new, but you’re still stuck with the costs while you’re renovating.

For Ikano Bolig, it will cost DKK 3,000-4,000 more per square metre to preserve Høje Taastrup’s old town hall than to demolish it.

“Right now it’s more expensive to transform a building than to build a new one, which is somehow insane,” says René Brandt and continues:

“But I hope that with this project we can help change that.”

Therefore, Rune Andersen believes it is necessary to regulate construction and make it more attractive to renovate by rethinking what makes a building worthy of preservation.

“The only tool we have to regulate demolitions is to make buildings listed or protected,” he says.

Today, very few buildings are listed. At the same time, buildings built after 1960 are typically not examined for preservation value because they were considered new when the so-called SAVE system was introduced in the 1990s for mapping and designating buildings worthy of preservation. Instead, Rune Andersen suggests updating the SAVE system and introducing a climate-related preservation value that examines how easily the building can be converted, and the potential to save CO₂ emissions if it is preserved.

“You could imagine that municipalities in the future will reject a demolition because a renovation will create a major climate benefit, whereas today the arguments are mainly architectural or historical,” says Rune Andersen.

Rune Andersen highlights three examples of good transformations of buildings: Hermodsgade 26, Nørrebro. “The building has been both transformed and densified by building on top. This solves the challenge of the lower construction rate in many existing buildings,” says Rune Andersen. Photo: Holscher Nordberg

Siljangade 4-8, Amager. “Offices are a type of building that is often demolished, but which has a construction principle that is relatively easy to transform, which we are also seeing more examples of now, especially for student housing,” says Rune Andersen. Photo: MuusFoto

Ørsteds Haver, Frederiksberg: "Shows that with some simple tools you can completely change the expression of a building and make it more attractive, thereby avoiding demolition," says Rune Andersen. Photo: Hampus Berndtson for Tegnestuen Lokal

Facts

Renovations have to be more competitive

We need to build more circularly, but the problem is that most circular solutions are not yet scalable, so it doesn’t always make financial sense to renovate or transform rather than demolish.

Christian Thuesen, Associate Professor at DTU Engineering Technology, hopes to change that through the CircOp project: Circular construction platforms.

“We want to do for circular construction what Tesla has done for the automotive industry—driving productivity in a new market until it becomes competitive,” he says.

The problem is that renovations are often complex and uncertain projects that make it expensive to reuse materials such as bricks, but in this project, Christian Thuesen is collaborating with a number of construction companies on minimizing waste across processes.

“It’s about thinking industrially rather than project by project,” he says.

By focusing on recurring problems, they gather knowledge from each project and make it available across projects. It creates a knowledge infrastructure that can lay the foundations for transforming the industry.

“The industrial mindset can help scale and accelerate, and we need that so that recycled materials are not just for wealthy suburban municipalities,” says Christian Thuesen.

New approach

For Ikano Bolig, preserving the town hall has brought a number of additional benefits. The building has a 5,000 square metre basement area that they would not have had otherwise, they reuse wooden boards and solid doors, and the existing trees and paths are also preserved.

Overall, Rune Andersen believes that renovations and remodelling are on the rise. Figures from the Danish 2024 Developer Barometer (Bygherrebarometeret) show that developers are increasingly carrying out renovations, while new construction is declining.

“We’re seeing more and more projects, especially in Copenhagen, where developers are thinking about transforming rather than demolishing. So I think the mindset is changing,” says Rune Andersen.

Fakta

Sustainable construction

Around 22 per cent of Denmark's carbon footprint comes from the building and construction sector. By building more sustainably, we can reduce energy consumption and thus greenhouse gas emissions.

Contact

Rune Andersen Assistant Professor Department of Environmental and Resource Engineering Mobile: +4593510447 runan@dtu.dk