One way or another, more additional homes need to be created in the near future. The challenge is even greater in cities because where can the space be found to build something new? The answer is almost nowhere. And so, 'vertical expansion' of existing buildings is now seen as one of the solutions to realise more homes in urban areas. As a structural specialist, Iv is often involved in such projects because creating a few extra storeys in itself is not complicated, but carrying it out in a structurally safe, responsible and realistic way often is.

"This is great fun if you like puzzles.''

An example is the Burgemeester Feithplein in Voorburg. Three additional levels have been built on both office buildings - now homes. As a result, the buildings are no longer comprised of 17 but 23 residential storeys. Iv investigated the feasibility and provided the structural design of the 'vertical expansion plans'.

Although it seems simple in theory to provide flat-roofed buildings with a few extra storeys, in practice, it is not so straightforward, says Rinske Daniëls-de Waard, Project Manager at Iv. "In terms of foundation and supporting structure, a building is constructed in such a way that it can support the structure. Buildings are not often designed to support additional storeys, mostly due to cost. Often, one extra storey can be built on top, but even then, it is a very complicated puzzle to evaluate how it can be done in a structurally safe way."

Vertically expanding a building mainly affects the stability and the wind load on a building. The higher a building, the more wind it will catch and the stronger the structure must be to absorb the load. Because of this, the work often does not end with the design of an additional storey but extends into various adjustments to the existing structure.
.

"Politicians need to make choices.''

Rinske: "What is not preferable is to interfere with the foundation because that has a lot of impact and is very expensive. This is why we first conduct a feasibility study, which requires archive documents of the foundation and the stability system. Even when the foundation is suitable for vertical expansion, reinforcement measures to the rest of the building are almost always required. These are often concentrated in the core of a building, where the lifts, stairs and shafts are located. This is where the wind load is mainly absorbed. Adjustments to other parts, such as floor and wall openings or openings through load-bearing parapets, like the new balconies of the Burgemeester Feithplein, are also always necessary. As structural engineers, we provide input on how to link data and calculations. In contrast to new designs, you are making use of something that already exists, and you continue on that basis. That's a lot of fun if you like puzzles. Fortunately, we do."

In short, vertical expansion of buildings is not as simple as it sounds. A lot of time is spent, especially in research and calculations, and ultimately, something will always have to be adjusted in an existing building to support the extra storeys.

Besides vertical expansion, repurposing buildings also contributes to solving the housing shortage. The Baumann Church in Overschie, Rotterdam, is an excellent example. This monumental post-war church has been transformed into a unique residential building. Iv was engaged in this transformation, from the feasibility studies to supervising the implementation. Repurposing is similar to vertical expansion in that it maximises existing buildings' use to give more people a home.

"Making sustainability cheaper on balance.''

An essential condition for building owners to be eligible for vertical expansion or repurposing is that the documentation is optimally in order. Iv, therefore, begins with archival research. Particularly for buildings built from the 1980s onwards, all the necessary paperwork is generally available, but we also have a lot of experience with buildings from the 1950s-1960s or even earlier. So, there are potentially many opportunities in urban areas to accommodate more people.

According to Jeroen Pahud de Mortanges, Director of Iv-Bouw, being creative and clever with existing buildings is the way to combat the (inner-city) housing crisis. "It's useful in urbanised environments because there is little space left. But on top of that, it's cheaper than new construction and much more sustainable."

It is also the ultimate opportunity for homeowners, especially those living in an older building, to achieve greater sustainability. Jeroen: "You can house more residents in the same building. Property owners are often united in an Owners' Association (VvE), so the costs related to installing solar panels or other sustainability initiatives can be spread over more people, making sustainability cheaper on balance."

In summary, it seems clear: vertical expansion and repurposing buildings, as is often done in Berlin, appears to be a relatively simple and accessible way to create additional homes quickly without branching out to rural areas. But it is not yet happening on a mass scale. As far as Jeroen is concerned, this is partly because the government has yet to chart a course to address the housing shortage and the role of nitrogen emissions in the construction sector. "As a result, a growing wait-and-see attitude can be observed within this market. And if anything is killing it, that's it. Politicians need to make choices. An additional 900,000 homes must be achieved by 2030. Last quarter, 15,000 permits were granted, which confirms the vacuum the construction world is in. So, something has to happen. Vertical expansion and repurposing offer a solution. The potential is huge, and we will happily use our expertise to harness this potential."