What advice would you give a client who is faced with the choice between demolition or transformation of a building?

First and foremost, you have to ask yourself whether you can afford to demolish and build new. It's costly - both in terms of the bottom line and sustainability - to renovate and build new. Often a house or building has a value that is lost when it is demolished. At the same time, you need to be prepared for the fact that a local plan must be drawn up and that it can be a cumbersome process. Especially when a building is located in a city centre, it is a costly and slow affair. Before we started transforming the Copenhagen shopping centre Illum, the developer considered demolishing the existing building. But it turned out to be a better solution to simply remove the top floor and then transform, so no new local plan was needed, we saved a lot of time and the slightly lower building blended in much better with the surrounding cityscape.

What are the complexities of transforming?

Transforming can be complex and it is extremely important to aware of the potential risks involved. When we started the transformation process of the SHELL building, it became clear that the building was constructed at a time when there was a shortage of good building materials. This meant that we couldn't be sure what was hiding behind the facades and walls. Sometimes it can be necessary to peel off a lot of layers before you can assess whether a building can withstand a transformation, and be aware of the fact that there can be risks associated with work that is unpredictable from the start.

When you transform, it's a bit like a tango dance. It's unpredictable, but it's exciting. It's not a linear process like new builds - it's an adventure, working with possibilities and potentials rather than just one solution. It takes love, agility and risk-taking, but the nugget of gold that you can create by working with the existing is extremely valuable. It's worth everything and then some.

Transforming buildings with a high quality outcome is all about recognizing opportunities - even where they are hard to see. For example, many people found it difficult to see the potential in KB32, especially from the outside, where it was very rough and run down. But there was no doubt when we stepped inside. A building of this nature will not be built again. This was a huge blank canvas to work with - a place full of possibilities.

What are the most important things to keep in mind when transforming buildings?

It can't be emphasized enough how important it is to thoroughly understand the details, history and layers of a building before you start transforming it.

As an example, I'd like to mention our work on transforming Illum in Copenhagen. This is a building that has undergone change and been tinkered with by different architects over a very long period of time, from 1860 all the way up to 1970. Thus, you can't just say that the building is put together in one way. There are many approaches, materials from different eras and different styles to consider in the process.

It's a good idea to familiarize yourself with how a building was conceived and learn what mistakes have been made over the years, but also what good ideas need to be revived. As architects, we must always do better than those who started, and we do this by learning from the past. This way, we can make smart decisions based on what's already there.

When I work with transformation, I don't aim to return everything to the way it used to be. But it is important when transforming to respect the professional choices that have been made in the past - to try to understand what they have achieved, what function have previous design or material choices had, and what no longer works?

What are the implications for urban development when transforming?

Working with the existing building stock creates a good dynamic in a city. The Aarhusgade neighbourhood in Nordhavn is a good example. There is an exciting variety of buildings. A three-bedroom apartment is not the same all the way through. They are different in their expression and are integrated with the surrounding city, backyards and city life. At the same time, old buildings allow for flexibility when transforming them. For example, you can move a downspout. You can't do that in a new apartment block.

I think that when you look out into the world, there are several scary examples of what happens if a city ONLY consists of new buildings - just look at the Parisian suburbs. Both the look and the mix of residents become too similar. Diversity is needed to create the good city.