The summer is approaching. We’re undoubtedly in for some heatwaves again, with long periods of drought, tropical nights, and sunburn warnings.

Even in the Netherlands, heatwaves are becoming longer, more frequent, and hotter. This trend will only worsen in the near future. We can’t easily reverse it, so we must learn to live with it—by going to the beach more often or taking more siestas, for example.

Or by implementing Blooming Buildings’ Heat Plan: more nature in the city.

Heat stress is bad for your health

In the spring of 2024, a group of Swiss women won a climate case against the Swiss government. These “climate grannies,” as they called themselves, argued that their government had not done enough to address the effects of climate change. One reason for their action: the increase in heatwaves and heat stress causes higher mortality rates among older people each year. This is also true in the Netherlands. The Central Bureau of Statistics saw a clear link between high mortality in the second quarter of 2023 and the heat. June of that year was the warmest June ever recorded.

For the elderly, babies, and other vulnerable groups, climate change is directly life-threatening. For people who work outdoors all day (such as street workers), dehydration, overheating, and sunburn are real dangers. For most people, it’s simply very unpleasant. You know the feeling of being unable to escape the heat in your home. You’re much less productive in an overheated office and can barely muster the energy to walk to the water cooler for refreshment.

The problem: heat is worst in cities

Asphalt, concrete, bricks, and roof tiles retain heat. During the day, when the sun is at its peak, this can become unbearable. In the evening, as shadows grow, the city continues to radiate heat. And even at night, the heat lingers. In the coming years, more people will live in cities, and more people will suffer from the urban heat island effect—the temperature difference between urban and rural areas.

Fortunately, there is a solution. A solution with many beautiful side effects. The city becomes more attractive, productive, and social.

The solution: more nature in the city

Nature has a cooling effect, thanks to shade and water evaporation. How strong this cooling effect is depends mainly on the amount of greenery. The greener our streets, walls, and roofs, the cooler the city. And size matters: trees with large canopies provide more shade. Planting trees in large areas, such as parks or urban forests, can create cool islands in the city—oases in the overheated urban desert.

But even if you have less space, a bit of nature in and around a building can work wonders. Not only does it cool the exterior, but the insulating effect of plants can also make the interior more comfortable.

Despite this being well-known, the insulating effect of plants is not yet considered in Dutch policy. When building new homes, measures to prevent overheating are assessed, but the cooling power of nature is overlooked (see TOjuli). A missed opportunity. If the building code gave points for this, the solution would be used more often.

How to cool a building with nature

You often see buildings with entire trees on balconies. This looks spectacular but is not a good solution. The trees cannot root deeply enough, it takes a lot of energy to lift them up, and the balconies must be reinforced to prevent collapse. What is the right approach?

We also love vertical greenery but prefer climbing plants. Planting them in the ground is one of the most effective and CO2-free ways to cool a building from the outside. Research has shown that a climbing plant covering 10m² can replace an air conditioner running at full capacity (300W) for 8 hours.

You can also green roofs effectively. We’re not big fans of sedum roofs. They often require too much plastic, need relatively high maintenance, and have an inverted day-night cycle. Plus, they don’t have much aesthetic value. Instead, we prefer to create a soil layer in which plants thrive.

Plants also work wonders for your indoor climate. Water evaporation cools the air and significantly improves air quality, which is often lacking in older office buildings.

For evaporation to occur, there must be enough water. Therefore, it’s essential to use high-quality materials: good soil, the right plants, and an intelligent irrigation system. This ensures water is absorbed and retained, ready to be used during dry periods.