New questions that buyers and tenants are asking before signing
During a visit, questions about thermal performance have long focused almost exclusively on winter. What is the heating system? Is the building well insulated? What are the energy costs?
Now, another question is being asked more and more often: how does the property behave when it gets very hot?
This is all the more relevant as Switzerland is warming up rapidly. According to MeteoSwiss, the average temperature in the country has risen by more than 2 °C since the start of measurements in 1864. Heat waves, tropical days and nights when the temperature does not drop below 20 °C are becoming more frequent and more intense. In cities, the urban heat island effect further limits nighttime cooling.
These changes are beginning to affect the way some buyers and tenants evaluate a property. They also directly affect real estate professionals: summer comfort is now a factor in the questions asked during visits, in the presentation of the property and, gradually, in the assessment of its long-term quality.
A favorable exposure in winter is not always favorable in summer
A south or southwest exposure is still desirable for natural light and solar heat gain. However, in summer, it can become problematic if the façade includes large, unprotected glazed areas.
Orientation is therefore not the only factor. To assess the risk of overheating, you must also consider the size and type of glazing, solar protection, the floor level, the shade provided by trees or neighboring buildings, and the possibility of creating a cross-ventilation. The exposure of the roof and the facades also matters, as does the ability of materials to temporarily absorb heat.
A large south-facing bay window, but protected by effective exterior blinds, can provide better comfort than a smaller window facing west that is exposed to the sun. In the west, the radiation hits the glazing directly at the end of the day, after the building has already accumulated heat for several hours.
The situation of attic dwellings must be examined with the same care. Their summer behavior depends on the insulation of the roof, but also on its exposure, color, thermal mass and the possibility of evacuating heat at night.
It is therefore too simplistic to qualify an orientation as “good” or “bad”. What matters is how the dwelling as a whole reacts to the sun.
Sunshades must be described precisely
A significant amount of heat enters the building through windows. Once solar radiation has passed through the glazing, interior blinds or curtains can no longer prevent all of this energy from being converted into heat in the room.
The Federal Office of Energy therefore recommends, as a priority, mobile sunshades installed on the outside of the building and covering the entire glazed surface. Venetian blinds, shutters, awnings and sun visors block the radiation before it reaches the glass. Some automated devices adjust their position in response to the amount of sunlight, the position of the sun or the strength of the wind.
In an advertisement or sales brochure, the word “blinds” alone provides little information. A buyer concerned about summer comfort will want to know:
- whether the blinds are inside or outside;
- which windows they cover;
- whether they can be operated when the unit is unoccupied;
- whether they are manually, electrically or automatically operated;
- whether they automatically retract in windy conditions;
- what other protection is provided when the blinds cannot be lowered.
The last point can make a real difference in high-rise units. In strong winds, some exterior blinds must be retracted, even on hot, stormy days. Their presence does not guarantee that they can be used in all conditions.
For the agent, it is useful to note the type of protection, the method of operation and the facades they cover. This information gives the buyer a much clearer picture of how the unit will behave in summer.
Opening windows at night is not always possible
Nighttime ventilation remains one of the most effective ways to get rid of the heat that has built up during the day. However, this is only possible if the building and its surroundings are suitable for it.
The outside air must first cool down sufficiently. Then, several windows must be able to be opened to create a draft, ideally on two different sides of the building. However, safety concerns, traffic or train noise, and nighttime activities in the neighborhood can make this solution difficult to implement.
A corner apartment has an advantage here. But this advantage is relative if one of the sides faces a noisy road or if the ground-floor windows cannot be left open at night.
Acoustic comfort and thermal comfort can even be at odds with each other. Good windows effectively block out noise when they are closed. If the noise level in the surroundings forces residents to keep the windows closed during a heat wave, the building will no longer benefit from nighttime ventilation.
The presence of mechanical ventilation does not necessarily solve this problem. A system designed to renew the air does not necessarily have the required flow rate to cool the rooms. Its nighttime operation and the possible presence of a summer bypass must be checked before it can be credited with a noticeable effect on indoor temperature.
Marketing documents should therefore avoid confusing three different functions: hygienic air renewal, nighttime cooling, and active cooling of the premises.
Good insulation can also retain heat
Insulation remains essential to slow down heat exchange between the interior and exterior. It is particularly important for homes located under a roof that is very exposed to the sun. But it is not enough on its own to guarantee a comfortable temperature in summer.
When the sun enters through large windows, when equipment and occupants generate heat, and when that heat cannot be released at night, even a very high-performance building envelope can end up trapping heat inside.
The result depends on several factors that work together: the quality of the insulation, the control of solar heat gain, the ability of walls, ceilings and floors to temporarily store heat, nighttime ventilation, and how the building is used.
Thermal mass is still rarely mentioned during a visit. Yet, heavy elements left exposed can absorb some of the heat during the day and then release it when the temperature drops. Some false ceilings, coverings or wall panels, on the other hand, limit access to this storage capacity.
The year the building was constructed or a general indication of the thickness of the insulation is therefore not enough to judge summer comfort. Documents prepared during construction or renovation will generally provide more reliable answers.
Reversible heat pump: what can the system actually do?
The presence of a heat pump is sometimes interpreted as a guarantee that the building can be cooled. This is not always the case. Not all installations have this function and, where it does exist, the results vary depending on the technology used.
Active cooling involves the heat pump extracting heat from the building. Passive cooling, or free cooling, uses certain geothermal installations or a water source. A chilled ceiling lowers the temperature more moderately, without achieving the performance of air conditioning. Air-to-air systems, on the other hand, can blow cold air directly into the rooms.
With a geothermal probe, passive cooling transfers some of the building’s heat to the ground, consuming relatively little electricity in the process. This heat can also be used to regenerate the ground thermally before the next heating season. However, the installation must have been designed and equipped for this purpose.
A chilled ceiling provides a more gradual temperature drop. It also requires precise control of the water temperature to prevent condensation.
Before you can say that a heat pump is “reversible,” several points need to be checked:
- Is the cooling function actually installed and activated?
- Which rooms benefit from it?
- How is the coolness distributed?
- Is it active or passive cooling?
- What prevents condensation?
- What is the energy consumption and what are the costs?
- What local regulations or permits apply?
In Switzerland, energy regulations for buildings are largely the responsibility of the cantons. Therefore, the requirements must be checked locally, especially when a property owner wants to add a cooling system or an outdoor unit.
Comfort also depends on the street and the neighborhood
Two similar apartments a few blocks apart may not experience the same temperatures in summer.
Asphalt, concrete and other mineral surfaces absorb solar energy during the day and release it slowly at night. In a very dense urban area, buildings can also impede air circulation. Trees, permeable soil, green spaces and bodies of water, on the other hand, provide shade and contribute to local cooling.
MeteoSwiss observations show that the urban heat island effect is most noticeable at night. Between 2018 and 2024, some stations in the center of Swiss cities recorded several tropical nights, while such nights were almost non-existent in some peripheral areas.
The proximity of a park is therefore no longer just an aesthetic advantage or a place for leisure activities. It can also have an effect on the temperature felt in the home. At the level of the building and its plot of land, it is worth observing the amount of green space, the shade actually provided by the trees, the distance to large asphalted areas, the air circulation and the heat emitted by traffic and technical installations.
These characteristics are not always easy to describe in a short advertisement. They can, however, be noted during the preparation of the mandate and explained during the visit. Several cities and cantons also publish climate maps that show the locations of heat islands and cold air corridors.
What information should be added to the property file?
Heating and energy consumption are usually well documented. The summer behavior of the property is usually much less well documented. However, some information collected from the owner, the management company or the developer would allow us to answer clients’ questions more precisely.
A summer comfort sheet could include:
- the orientation of the main rooms;
- the type and location of sun protection;
- the ventilation system and its different modes;
- the possibility of creating cross-ventilation;
- the presence of any cooling system;
- any work done on the roof or facades;
- the specific features of attic or loft apartments;
- the vegetation and shade sources around the building;
- any indoor temperature readings.
However, these measures require a minimum of context. A high indoor temperature at a given time does not mean much if one ignores the outside temperature, the time of day, the use of blinds, the number of people present and the duration of the heat episode.
The occupants’ perception can also provide useful information. However, it is still related to individual habits: ventilation schedules, use of sun protection, appliances in operation, and personal tolerance to heat. This testimony should not be turned into a general promise without further verification.
A new criterion to weigh in on the decision
Light, quiet, views and proximity to public transport will remain central to the search for a home. But buyers are also starting to ask whether the property will still be livable after several days of extreme heat.
Real estate professionals don’t need to present every property as being perfectly prepared for heat waves. Instead, they should know how the property actually works, avoid making overly general statements and provide verifiable answers. A heat pump is not necessarily an air conditioning system, good insulation doesn’t prevent all overheating, and the presence of blinds doesn’t guarantee that they can be used all the time.
This analysis can also help homeowners decide which improvements are most useful: installing exterior sunshades, creating more shade, adapting ventilation, working on the roof or installing a cooling system that is compatible with the building. These improvements are sometimes less noticeable than a new kitchen or a new façade, but their impact on the daily use of the property could become an increasingly important factor in the decisions of buyers and renters in Switzerland.