How can schools stay cool during heatwaves without mechanical cooling? Discover how dynamic solar shading improves comfort, reduces energy use and supports EPBD objectives.
Léa Sellitto, Somfy Group
Alexis Damia, Somfy Group
(Note: Opinions in the articles are of the authors only and do not necessarily reflect the opinion of the European Union)
Across Europe, rising temperatures and more frequent heatwaves are transforming how buildings perform in summer conditions. Classrooms, in particular, are becoming increasingly vulnerable to overheating, with direct consequences for pupils’ learning capacity, teachers’ working conditions and overall occupant well-being. Despite this, summer thermal comfort has long remained a secondary consideration in building policies primarily focused on winter energy performance.
The recast Energy Performance of Buildings Directive (EPBD) marks a significant shift. For the first time, overheating risks, indoor environmental quality (IEQ), and climate adaptation are explicitly recognised as key components of building performance. This evolution reflects a broader transition from purely energy-efficient buildings to human-centred buildings, where comfort, health and climate resilience are central objectives.
In this context, passive cooling solutions are gaining renewed attention as cost-effective and scalable strategies to mitigate overheating without increasing energy demand. Among these, well-managed external solar shading is one of the most effective ways to control solar gains at source.
The case of the Poissy schools in France, provides a concrete and measurable example of this approach. Faced with increasingly severe summer conditions, the municipality implemented a large-scale deployment of motorised external blinds across 15 school buildings. The results demonstrate how simple, well-designed interventions can significantly improve indoor comfort, reduce energy consumption and contribute to the objectives set by the EPBD.
For decades, European building policies have focused primarily on reducing energy consumption, particularly for heating. While this approach has improved winter performance, it has largely neglected a growing issue: overheating.
Meanwhile, climate change is reshaping the conditions most buildings were designed for. By 2040, around 85% of the European building stock will consist of buildings that already exist today. These buildings were largely optimised for colder climates and are often ill-equipped to cope with longer, more frequent and more intense heatwaves.
The recast EPBD introduces a major shift in perspective. By integrating IEQ and requiring Member States to develop climate adaptation plans, it makes clear that energy performance alone is no longer sufficient. Buildings must also protect occupants against overheating, ensure comfort and safeguard health.
This evolution is particularly important for schools. As public buildings hosting children, they must provide safe and healthy indoor environments under all climatic conditions. Overheating is not only a comfort issue, it directly affects concentration, cognitive performance and overall well-being. Ensuring adequate thermal and visual conditions in classrooms is therefore both an educational and a public health priority.
The rise in cooling demand across Europe is one of the most visible consequences of climate change. As temperatures increase, more buildings rely on air conditioning to maintain acceptable indoor conditions.
However, this trend raises several concerns. First, it increases overall energy consumption and associated costs for both public authorities and households. Second, it intensifies peak electricity demand during heatwaves, placing additional strain on already stressed energy systems. Third, it creates a feedback loop in which rising cooling demand drives higher emissions, further exacerbating climate change and urban heat island (UHI) effects.
In this context, relying solely on active cooling systems is neither sustainable nor resilient. It risks locking buildings into energy-intensive solutions that may not be viable in the long term.
A more effective approach consists of preventing overheating at source. This means limiting solar gains before they enter the building envelope, rather than compensating for them afterwards with mechanical cooling.
Among passive cooling strategies, dynamic solar shading is one of the most efficient and immediately deployable solutions. By blocking solar radiation at the façade level, it significantly reduces the amount of heat entering indoor spaces.
In practice, adding external shading to modern double-glazed windows can reduce solar gains by up to 80%. During heatwaves, this can translate into indoor temperature reductions of 4 to 7°C, substantially improving thermal comfort.
Beyond summer benefits, solar shading also contributes to winter performance. By allowing solar gains during the day and reducing heat losses at night, it can lower heating demand and improve overall energy efficiency.
This dual functionality makes external shading a particularly relevant solution in the context of the EPBD, which aims to balance energy performance with occupant comfort throughout the year.
In the summer of 2020, the City of Poissy, located in the Greater Paris region, faced a pressing challenge: how to maintain comfortable indoor temperatures in public schools during heatwaves without installing energy-intensive air conditioning systems.
Rising temperatures and UHI effects were making classrooms increasingly difficult to use. Pupils struggled to concentrate and teachers faced deteriorating working conditions. In response, the municipality launched a proactive heatwave action plan.
Over a three-year period, with works scheduled during school holidays to minimise disruption, the city retrofitted 15 public school buildings with 616 motorised external ZIP blinds. This intervention transformed windows from sources of overheating into effective regulators of indoor temperature.
The decision was supported by technical studies comparing different retrofit options. External solar shading emerged as the most cost-effective solution for reducing overheating while maintaining access to natural daylight.
Figure 1. School in Poissy. Source: City of Poissy.
The results of the Poissy project highlight the effectiveness of dynamic solar shading in real conditions.
In terms of thermal comfort, indoor temperatures were significantly reduced. Classrooms equipped with the new motorised external blinds were up to 5.1°C cooler than those with older manual shading systems. During extreme heat events, with outdoor temperatures reaching 39°C, indoor temperatures remained below 27°C, representing a difference of up to 12°C.
From an energy perspective, the impact is equally significant. The installation saved approximately 301,000 kWh per year compared to a scenario relying on air conditioning to achieve similar comfort levels (27°C inside the classroom). This translates into annual savings of around €200,000 in energy and maintenance costs for the municipality, excluding installation costs.
The initial investment amounted to approximately €812,000, corresponding to around €54,000 per building. The payback period is estimated at around four years, demonstrating the strong economic viability of the solution.
The Poissy case illustrates how climate adaptation, energy efficiency and occupant well-being can be addressed simultaneously. Rather than treating these objectives separately, they should be considered interconnected dimensions of building performance.
It demonstrates that improving indoor environmental quality does not necessarily require complex or expensive solutions. Simple, well-targeted interventions can deliver substantial benefits in terms of comfort, energy performance and resilience.
As climate change intensifies the frequency and severity of heatwaves, it is essential that renovation policies, new building regulations and national-level programmes explicitly include summer thermal comfort as a standard objective for new and existing buildings. This includes setting clear performance indicators, adapting climate targets in calculation methodologies and offering targeted support for solutions that prevent overheating. Addressing this issue at an early stage will improve occupant health and well-being.
The retrofitting of the Poissy schools also highlights the importance of adapting the existing building stock. Since 85% of European buildings that will be in use in 2040 already exist today, renovation strategies must prioritise scalable and cost-effective solutions. Despite its proven effectiveness, dynamic solar shading is not yet systematically recognised as a core building system. Including it more explicitly in EPBD implementation could accelerate its deployment and its proper management through building automation and control systems (BACS).
The transition from smart buildings to human-centred buildings requires a broader understanding of performance, one that fully integrates comfort, health and resilience alongside energy efficiency.
The Poissy schools project demonstrates that passive cooling solutions such as dynamic solar shading can play a central role in this transition. By significantly reducing overheating, lowering energy consumption and improving indoor conditions, they offer a practical and scalable response to the challenges posed by climate change.
As the EPBD moves into its implementation phase, the priority should be to ensure that such solutions are widely deployed, particularly in existing buildings. Making summer thermal comfort a standard objective of renovation policies will be essential to creating buildings that are not only efficient but also truly fit for a changing climate.
