Cool roof for schools: cooler classrooms, no air conditioning, applied over the holidays

Heatwaves at school: a school-calendar problem

School buildings were designed for winter: to retain heat, light the classrooms and withstand the wind. Nobody imagined that heatwaves would arrive in June, during exams, and in September, at the start of the school year. Yet that is what has happened every year since 2019, and the mayor, who owns the nursery and primary schools, ends up responsible for rooms at 35 °C. The département for lower secondary schools (collèges) and the region for upper secondary schools (lycées) face the same problem over larger surfaces.

June and September: the hot months are school months

A school is occupied during the most exposed periods of the school year: the last three weeks of June and the first four weeks of September. Under a bitumen flat roof, the surface temperature reaches 50–70 °C by 1 p.m. and radiates into the top-floor classrooms until the evening. The rooms do not cool down overnight, and the next day starts at 27 °C. Our page on heatwaves and building protection describes what to anticipate before summer.

What heat does to pupils and teachers

Above 28 °C, attention drops, fatigue rises, children become restless or fall asleep, and teachers scale down their teaching. The youngest, in nursery school, regulate their body temperature poorly; asthmatic or fragile children are the first affected. Catering staff, in kitchens under steel deck, and nursery-school assistants (ATSEM) also face arduous working conditions on top of it. A classroom at 26 °C instead of 32 °C is not a matter of comfort: it is the condition for finishing the school year.

The heatwave protocol has its limits

The protocol calls for airing early in the morning, closing the shutters, handing out water, avoiding physical activity and installing fans. When the heat comes from the ceiling, these measures are no longer enough: the radiation from the slab gets through everything. What remains is closing the school, decided in a hurry, with parents having to make arrangements. A cool roof removes this heat at the source, once and for all, without consuming a single kilowatt-hour.

What PrimaTherm® changes on a school

Hélios applies the PrimaTherm® system, made in France by Primacoating: a water-based, solvent-free elastomeric coating applied in 4 layers (PH169 primer, PH107 reflective base coat in two cross passes, PH107TCL anti-soiling topcoat). Every value below is measured in the laboratory; the reports are attached to the offer and can be required in the specifications.

In a school:

• up to −30 °C on the roof surface: from 50–70 °C down to 25–35 °C, with −29 °C measured by infrared at the handover of a 5,900 m² project in 2026;
• up to −6 °C felt in the classrooms under a poorly insulated roof, 1 to 3 °C in a well-insulated building, and the end of the heat radiated by the ceiling;
• air conditioning avoided, so no additional consumption to declare on the OPERAT platform for schools over 1,000 m² covered by the French tertiary-sector decree;
• waterproofing that lasts longer, because it no longer cycles between 20 and 70 °C every summer day; that is a re-roofing pushed back in the multi-year investment plan;
• a visible signal for families and the school council: the local authority acted before the next summer.

The reference: a 1,000 m² school in La Rochelle

The case we present to local authorities is a 1,000 m² school in La Rochelle, a Hélios project: bitumen-membrane flat roof, combined with photovoltaic panels, applied during the holidays. The local authority was planning to air-condition the classrooms; after treatment, the air conditioning was no longer necessary. The details are on the La Rochelle school page. In the same urban area, 1,500 m² of EPDM-roofed offices and a 3,000 m² food-processing plant were also treated by our teams with the same system.

For large surfaces, our reference is a 5,900 m² bitumen-membrane project on three buildings, treated from April to June 2026 on an industrial site in operation, with −29 °C measured at handover (57.8 °C on the untreated area versus 28.6 °C on the treated area). See the Airbus Marignane project.

Work during the holidays: from the May visit to the new school year under a white roof

The school calendar dictates the schedule, and it is favourable: the summer holidays coincide with the best weather window.

1. March to May: free study, technical visit of the roof, check of the substrate and equipment, costed proposal, documents for the funding application and the tender.
2. June: tender under the French public procurement code, prior declaration to the town hall if required, information to the school council.
3. July–August: preparation (cleaning at under 130 bar, anti-moss treatment, local repairs, 24 to 72 h drying), application in 4 layers, thickness checks, infrared measurements. A 1,000 m² school is treated in a few days.
4. Start of the school year: as-built file, ten-year liability cover (French décennale), maintenance plan handed to the technical services.

No crane in the playground

Our no-lift method keeps the 150 to 200 L drums and the airless pump on the ground, in a cordoned-off area of the playground or car park; only the hoses go up to the roof. No crane, no heavy aerial platform in front of the school, no road closed during the summer holiday clubs. The product is water-based, solvent-free and low in VOCs: nothing to remove, nothing to air out before the new school year.

Which school roofs

• Bitumen-membrane flat roofs of school complexes from the 1960s to the 1990s: the most frequent case, PH169 primer at 6 m²/L. See cool roof on bitumen roofs.
• Terraces: see cool roof on flat roofs.
• Covered playgrounds, canteens, sports halls and modular buildings under steel deck: primer at 10 m²/L, the most spectacular comfort gain. See the cool roof on steel deck roofs guide.
• Rooflights and light wells above corridors and covered playgrounds: PrimaTherm® LT semi-transparent lacquer (one coat: around −25 % heat gain and light; two coats: around −50 %).
• Photovoltaic roofs: treated between and under the rows, as in La Rochelle. See cool roof and solar panels.
• Exclusions: asbestos fibre cement (buildings from before 1997), PVC membranes less than 10 years old, tiled roofs with insulated attics, for which we point you towards other solutions.

Public-access buildings

A school is a public-access building (French ERP classification, type R): the fire safety committee looks at the fire performance of the roof covering. PrimaTherm® is classified Broof(t3) for external fire (CSTB report RA23-0010); the certificate is supplied with the file. Changing the colour of a roof generally requires a prior declaration to the town hall (article R. 421-17 of the French planning code), with the opinion of the French heritage architect (Architecte des Bâtiments de France) in protected areas; we check the local planning rules (PLU) for each school.

Funding a school cool roof

We prefer to be precise before the application is put together.

• French energy-savings certificates (CEE), sheet BAT-EN-112: no. The sheet targets commercial-use tertiary buildings heated and cooled by heat pump; a school does not qualify.
• MaPrimeRénov’ does not cover cool roofs.
• The French Green Fund (Fonds Vert): the fund for accelerating the ecological transition in local areas finances, through the prefectures, the energy renovation of local public buildings and adaptation to climate change, including the fight against overheating in schools. A cool roof is presented there with a diagnosis, certified values and expected measurements.
• DSIL and DETR: French state grants for local investment and for rural areas, available for the renovation of school buildings.
• Département and region: lower and upper secondary schools come under their multi-year investment plans, often with a “resilient buildings” strand.

We supply the technical documents for the application; the cool roof incentives in France 2026 page details the schemes. The cost depends on the surface, the substrate, the preparation, the access and the grants: it only exists in the proposal handed over after the free study. For the tender, the technical criteria can require the test reports, the ten-year liability certificate, the 4-layer protocol and the before/after measurements: the checklist for choosing a cool roof contractor (in French) serves as a template.

The cool roof as an educational project

A white roof is a concrete support for sustainable-development education: measuring the surface temperature before and after with an infrared thermometer, recording classroom temperatures over a year, the notions of albedo and radiation, the link with urban heat islands. Several schools include these readings in a class project; we provide the handover measurements (infrared before/after) as a starting point. See also cool roofs and urban heat islands.

The objections we hear in committee

• “We should insulate first.” Winter insulation does not solve summer: the roof heats up, the insulation delays the heat and then releases it in the evening. A cool roof removes the heat at the source and combines with existing or future insulation. See external roof insulation (in French).
• “We might as well air-condition.” Air-conditioning a school means a heavy investment, consumption to declare on OPERAT, noise and maintenance. In La Rochelle, the planned air conditioning was no longer necessary after the cool roof.
• “A coating is a gimmick.” An off-the-shelf white paint reflects 70 to 80 % of the radiation and loses its whiteness within two seasons. PrimaTherm® reflects 95 %, keeps its SRI after 4,000 h of accelerated ageing and is applied under a controlled protocol. The industrial clients who chose it do not buy gimmicks.
• “What about winter?” The low winter sun hits the façades, not the roofs; the loss of winter solar gain is marginal. See cool roofs in winter.
• “Who maintains it?” Low-pressure water cleaning every 12 to 15 months, which can be built into the technical services’ maintenance plan.

Establishments concerned

• Nursery and primary schools: municipality, flat roofs, covered playgrounds and canteens.
• Lower secondary schools (collèges): département, large steel-deck or membrane roofs, half-board catering.
• Upper secondary and vocational schools (lycées): region, workshops under steel deck, boarding houses under the roof.
• Nurseries and after-school centres: the most sensitive groups.
• School sports halls and holiday clubs: occupied all summer. See cool roof for public buildings.

From Saint-Laurent-d’Agny, near Lyon, we work on schools across the region on day trips (Lyon, Vienne, Saint-Étienne, Grenoble) and anywhere in France with a team accommodated on site during the summer (Marseille, Toulouse, Nantes, Paris). The cool roof simulator (in French) gives a first order of magnitude per building; the free study follows within 48 h, to be launched in spring for application during the summer holidays.