Heat waves create unhealthy indoor climate – Swedish houses need climate adaptation

But how can we follow this advice when our houses have been designed for a different purpose?

It is clear that heatwaves and their impact on the indoor climate of our buildings are becoming an increasingly serious problem. Swedes like to have large south-facing windows that let in plenty of sunlight, particularly in winter when it is so dark. However, during the summer, this can become problematic. 

"The design of a building is very important," says Jutta Schade, a senior researcher and project manager for Sustainable construction at RISE.

"This creates a conflict because there are requirements for buildings to have a certain amount of daylight. These aspects clash," says Peter Ylmén, Doctor of Technology and RISE expert specialising in energy simulation and sustainability issues related to buildings.

Proven effective: sun protection and ventilation.

Fortunately, there are relatively simple solutions for dealing with excessively high indoor temperatures. Sunshades in the form of awnings, for example, can block up to 90 per cent of the sun's rays before they have a chance to heat up the window glass and, consequently, the room. There are also solutions involving semi-transparent fabrics that let in daylight but block most of the heat radiation.

"We can solve a lot of problems by ventilating at night, when temperatures are usually lower. However, this requires you to be able to open your windows, which isn't always possible depending on where you live. In cities, smog and noise pollution can make us reluctant to sleep with the windows open. The effect is also reduced if you can only open windows on one side of the room, as is often the case in flats. Ideally, you want to create a draught," says Peter Ylmén.

Iordan Palma is a doctoral student at RISE and Malmö University, where he is researching settlement patterns within the population. His work involves studying literature on how overcrowding and high levels of airborne particles can affect cognitive function and academic performance. He has found that the poor ventilation conditions mentioned by Peter Ylmén are prevalent in areas with a low socioeconomic status.

"Tall buildings, which are particularly common in vulnerable areas, often have little sun protection and poor ventilation. This could suggest that excessive indoor temperatures are a more significant issue there. The combination of poor ventilation and a population consisting of many children and elderly people, who are at risk during heatwaves, means that the problem is likely to be particularly serious in these areas," says Iordan Palma.

Climate adaptations to reduce indoor temperatures.

Unlike in countries with a generally warmer climate, ventilation in Swedish buildings is usually designed to combat odours and moisture, rather than to manage heat.

"This needs to be taken into account during conversions, renovations and new builds. Many people choose to address the issue by installing cooling units, but this is not an environmentally friendly solution. Not only does this increase energy consumption, but it also results in extra equipment that needs to be controlled and maintained," says Peter Ylmén.

Phase change materials, which can store and release heat by switching between solid and liquid form, are another possible solution that is more energy efficient. When the indoor temperature rises above a certain level, the phase-change material — such as paraffin wax — melts, absorbing a lot of energy without itself becoming warmer. When the temperature drops, the material solidifies again, releasing the stored heat. Phase change materials can be incorporated into walls, ceilings or floors.

"However, it is quite expensive, and as far as I know, it has not had a significant impact. People are working on the issue, but I wouldn't say there's an innovative solution that's better than sunshades or ventilation," says Peter Ylmén.

Simulates how thermal energy moves in buildings.

RISE is at the forefront of building physics research, investigating how heat, air and moisture move in and through buildings and their materials. It also has a test bed for ventilation solutions and extensive expertise in urban planning, property development and architecture. Collaborating with the construction industry ensures that the ideas and solutions developed through research can be implemented in practice.

"At Building Physics, where Jutta and I work, we don't design buildings. However, we do help with energy and temperature simulations, and we can evaluate these by taking measurements on site. We provide support for the development of housing and buildings at all levels, from policy to individual properties," says Peter Ylmén.

The message from researchers is clear: sun protection, ventilation, and awareness of the risks associated with excessively warm living and working environments are a good place to start when it comes to addressing the increasing frequency and intensity of heatwaves.