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Opportunity to create more homes in cities: upward extension

February 28, 2022

The current state of the housing market is more pressing than ever. There’s a historical shortage of affordable housing, leading to long waiting lists for social housing. But there’s also good news: more and more housing associations are willing to invest in creating new housing. While investments have continually declined in recent years, they will increase significantly in the coming years. For example, in The Netherlands, a total of 33.5 billion euros is available for building new housing, which should accelerate the construction of a total of 150,000 new social houses.

As you can see, there’s no lack of ambition. But: where should all these new homes be situated? Particularly in urban areas, available land is scarce and housing shortage is alarmingly high. Also, it often takes a long time to get the right permits, not to mention finding enough construction personnel to carry out the ambitious plans.

Another possibility of achieving new construction goals: upward extension

That begs the question: are there any other possibilities available to build these 150,000 new social houses more quickly? One option to look at, especially in urban areas, is upward extension of existing buildings.

But this is easier said than done. Because some houses are better suited for upward extension than others. In addition, constructive research is always required to determine whether the underlying supporting structure is adequate.

When to use upward extension

The choice for upward extension is often made when a building is ready for renovation. The building can be upgraded by building an extra floor on top, installing elevators and creating a new entrance. The purpose of upward extension is then not only to create more living space, but also to achieve a better overall appearance of the building.

By building an extra floor on top, there’s the added bonus of creating more differentiation in the housing offering (by, for example, adding maisonettes in an apartment building). This way, different target groups in the same district can be serviced.

Requirements for upward extension

Buildings must meet several requirements to be eligible for upward extension. For instance:

1. Longevity

The extra floor on top is a new construction, so the entire building must be able to meet the expected lifespan of the construction. The building can therefore not be too old, but also, preferably, not too new: new constructions often require little or no renovation, so it’s less efficient to select these buildings for upward extension.

2. Roof type & surface

Upward extension is possible on buildings with a pitched roof, but adding a floor on a flat roof building is easier, because the waterproof layer of the existing roof can be kept intact as much as possible. Considering the surface area of the roof is important as well: the larger the surface, the more extra living space can be created.

3. Building height

Depending on the locally permitted maximum building height, upward extension can be done on both high-rise and low-rise buildings. High-rise buildings can, however, lead to a much more complex construction process, and regulations around adding floors to such buildings are also more extensive, for example with regard to fire safety.

4. Foundation

A building must have a solid foundation to be able to bear the extra weight of the new floor. However, it’s difficult to figure out what foundation the building was built on if original drawings and plans are missing. Technical research is often necessary here, although the subsoil can provide an indication of the foundation method that was used.

5. Construction

The construction of the building must be strong and stable enough to support the extension. This requires technical research. To keep the extra weight to a minimum, the extension will usually be built with light constructions like a steel frame or timber frame construction.

With so many requirements and a largereal estate portfolio; where do you even start unfolding this puzzle?

Making a first selection in your real estate portfolio

Thorough research is always required to actually select a building for upward extension. However, you can already start by making a first selection within your real estate portfolio to see which buildings might be decent candidates. Within Spotr, you can easily make this first selection, based on specific characteristics.

1. Lifespan: select year of construction

We can start by selecting buildings that are not too old for upward extension to become a problem (like homes from the 1920s). Of course it’s possible to choose older buildings that are ready for an extensive renovation anyway. But we'll leave this out for now. We are now only looking at buildings between 1980-2005. In our example portfolio, we then find 515 estates. That looks like this:

2. Roof type and surface: select Roof type 'flat roof'

We then move on to the roof type: which homes in the portfolio have a flat roof? This gives us 359 estates as result:

3. Building height: select 'Buildingheight' 5-15 meters

Next, we look at building height: let's say we think buildings between 5-15 meters are ideal for upward extension. Then we arrive at 245 estates:

4. Foundation: select the map layer 'Foundation problems'

The map layer 'foundation problems' can be placed over the entire portfolio, so we can easily zoom in on non-vulnerable areas:

As shown on the map, there are quite a few suitable homes that are located within vulnerable (purple) areas. But when we zoom in on non-vulnerable areas, we immediately see a few interesting examples of houses that might be suitable for upwards extension, such as this one:

Or, when specifically zoom in on a city like Amersfoort, we can see the following:

Here we find a number of interesting examples as well:

5. Construction: start further research on selection

Once you’ve made a selection of buildings that are interesting for upward extension, further research can begin. Is the construction suitable for upward extension? Are these estates already on the list for a renovation soon? But with a few simple steps you’ve been able to do valuable preliminary work on your entire portfolio.

Upward extension: an opportunity for your real estate portfolio?

How do you look at adding new houses to your real estate portfolio? Is upward extension a suitable solution? We’re happy to help you find out. Schedule a call with us for more information: