Livestock buildings and warehouses: the heat comes from radiation, not from the air

An empty shelf, and 700,000 missing hens

This photo has nothing to do with a supply glitch. At the end of June 2026, a heatwave pushed temperatures above 40 °C in regions of France unused to it, Brittany and Pays de la Loire first among them. The industry’s assessment is blunt: 700,000 laying hens lost, 1 to 1.5 % of the French flock according to the CNPO, and 2.5 to 3 million broilers according to Anvol. In a matter of days.

What the professionals said next is worth reading twice. Old buildings could not absorb the peaks; recent ones, better designed for insulation and ventilation, held. Natural ventilation, common in free-range and label production, paid the highest price. In other words, the difference between a farm that lost its flock and a farm that kept it did not come down to the weather, which was the same for everyone. It came down to the building.

A farmer does not only lose animals. They lose a whole flock, the cash that came with it, sometimes several weeks of production, and they spend the heatwave removing dead animals instead of doing their job. The retailer discovers an empty shelf and puts up an apology notice. In between, nobody has a solution on the day.

What heat takes, even before it kills

Mortality makes the headlines, but it is the end of a list. Before it comes to that, heat takes production away every day, quietly, and that loss never shows up in a rendering truck.

In laying hens. Researchers from INRAE and ITAVI pointed it out this summer: at a constant 32 °C, against the usual 22 °C, egg production falls by 15 to 30 %. Egg weight drops by 0.4 to 1 gram per degree above 25 °C, and shell quality deteriorates within the first days of exposure. A hen’s core temperature is around 41 °C: beyond 42 °C, prolonged exposure becomes lethal. The margin is narrow, and it closes from the top.

In broilers. The benchmarks of the ClimatBat network of the French chambers of agriculture put the thermoneutral zone of a growing bird at around 18 to 24 °C. Feed intake falls as soon as the indoor temperature passes 23 °C. Beyond 25 °C, the bird can only shed heat by evaporation, that is by panting, and the risk is assessed on a temperature-humidity index, severe from 73 and very severe beyond 78.

In dairy cows. Their thermoneutral zone lies between 2 and 15 °C, which often comes as a surprise. The index value of 68, the first stress threshold, is reached at just 22 °C and 50 % humidity, an ordinary summer day in mainland France. The review carried out by the French Livestock Institute (Idele) for the dairy interprofession Cniel puts figures on what follows: 270 to 590 grams of milk per index point, that is 2 to more than 4 kg per cow per day when the temperature rises from 26 to 33 °C. Under severe stress, breathing rises to 150 breaths a minute.

These figures describe very different buildings. A broiler house works on the floor, on litter, with a lighting programme, finely tuned ventilation and strict biosecurity. A laying house is organised around egg collection: dark nests with a sloping floor, belts that carry the egg to the grading room, multi-tier aviaries with perches, feeders and drinkers, and, in free-range and organic systems, pop holes opening onto a winter garden and then the outdoor range. A dairy barn is nothing like either. What they share is above the animals: the roof.

And the farmer, inside that building?

They work there. In France, decree no. 2025-482 of 27 May 2025 wrote it into the labour code in black and white: since 1 July 2025, employers must assess the risk linked to episodes of intense heat indoors as well as outdoors, record the measures in the risk assessment document and provide at least three litres of cool water per employee per day where there is no running water. A building whose roof radiates heat is not only a production problem. It is a workplace.

Do not confuse hot air with radiant heat

Here is the point almost everyone misses, and it changes the diagnosis completely.

You know the scene. A car left in the sun, door open: the air is stifling but breathable, and yet the steering wheel burns your hands and the dashboard is impossible to touch. This is not an impression. Researchers from Arizona State University and the University of California San Diego measured it, over three summer days in Tempe.

Look at the first column. Between the air an occupant breathes and the dashboard they touch, there are 22 degrees of difference, in the same space, at the same moment. Now look at the second: in the shade, the dashboard is only 10 degrees above the air. The whole difference between the two columns is radiation.

A metal roof does exactly what the dashboard does, on a larger scale. The order of magnitude is easy to work out: the surface overheating is roughly the absorbed solar flux divided by the external surface heat transfer coefficient, which EN ISO 6946 sets conventionally at 25 W/(m²·K). With 1,000 W/m² at the zenith, that gives:

These three lines are calculations, not measurements, and they ignore both wind and radiation to the sky. They are still enough: at 32 °C in the shade, a dark roof covering works at around 68 °C, its underside included since the sheet is thin. That underside radiates towards everything beneath it, and radiation crosses the air gap without caring whether it is ventilated. This is where ventilation reaches its limit: it moves air, it does not move radiation.

Radiative exchange between two parallel surfaces depends on the emissivity of both, through a mutual emissivity factor equal to 1 / (1/ε₁ + 1/ε₂ - 1). Between coated sheeting and a building floor, two surfaces around 0.9, that factor comes to 0.818. Replace the first with an underside at 0.053 and it drops to 0.053 as well: as soon as one of the two surfaces emits little, it is the one in charge, and the same temperature difference transmits only a fifteenth of the flux. The principle is set out on our page R'BULL technology.

The same problem, from Brittany to India

None of the above is peculiar to France. France accounts for only 10.6 % of European chicken production, behind Poland (19.5 %) and Spain (12.3 %), and the June 2026 heatwave swept across the continent: the empty shelf in the first photo could have been in any of those countries.

In the United States, the bill was worked out long ago, and it is annual, not exceptional. A study in the Journal of Dairy Science puts the losses of American livestock farming due to heat stress at 1.69 to 2.36 billion dollars a year, across all animals, with dairy bearing the largest share. Lower growth, laying, milk yield and fertility, plus mortality, added up year after year.

On a global scale, a model published in The Lancet Planetary Health in March 2022 projects, for cattle alone and by the end of the century, production losses of 39.94 billion dollars a year under a high-emission scenario, 9.8 % of the value of the meat and milk produced in 2005, and 14.89 billion under a low scenario. Two results stand out: cattle and dairy production in the United States would fall by 6.8 %, India would lose more than 45 % of its dairy production, and tropical regions take a far heavier hit than temperate ones.

That is exactly the map of our shipments. In the French West Indies, in French Guiana, and everywhere between the tropics, heat is not a three-day episode in June: it is the normal condition of the year. A building there spends its whole life under the radiation that mainland France only sees for a few weeks.

Regulations follow, each in its own way. The French overseas departments apply the RTAA DOM and its solar factor. The Indian state of Telangana has required reflective materials since April 2023, through its cool roof policy, on public and commercial buildings and on residential plots of more than 600 square yards, with a target of 300 km² of treated roofs. An honest clarification is needed: these rules target the outer face of the roof covering, which they want light-coloured and highly emissive towards the sky, whereas a thin reflective insulation works on the inner face, which it wants to be low-emissive towards the building. The two add up, at the two ends of the same roof.

What has already been tried, and why the load keeps coming back

Farmers have not sat and waited. They have ventilated harder, installed misting, sprinkled roofs, shifted working and feeding times, reduced stocking density, adjusted rations. After June 2026, a cooperative in western France set out to equip 170 farms with fans, at around 1,500 € each, 70 % funded. An enriched feed gains about 2.9 performance points over the stress period. All of this works, all of it is useful, and none of it should be dropped.

Look, though, at where each of these measures acts. Ventilation, misting, feed, lower stocking density all come in afterwards, once the heat is inside. They compensate. They cost electricity, water, noise, labour, and they cost all the more as the load to be compensated grows. On the day it passes 40 °C outside, the fresh air being blown in is also at 40 °C: ventilation no longer cools, it just stirs.

That leaves a question rarely asked: what does doing nothing cost? A lost flock, several weeks of poor laying, milk not produced every summer day, refrigeration running for nothing, staff slowed down, and the following year the same again, a little earlier and a little longer. Against that, a one-off intervention on the roof at least deserves to be costed.

The thermal shield under the roof

We are talking here about a solution that can, depending on the roof configuration, complement your construction choices where summer comfort is an identified issue. Not replace them.

That is the logic behind R'BULL Pro 13: a reflective thermal shield under the roof, designed to limit part of the radiant heat gains, as a complement to the existing insulation and ventilation. It does not blow air, it uses no energy, it needs no adjustment. It presents the building with a face that emits little, and the radiation coming down from the sheet no longer finds a way through.

What it does better than an ordinary underside comes down to one figure. The LNE measured its emissivity at 0.053 in its report P254377 DMSI/2, under annex D of EN ISO 22097:2023, the same annex that requires any value below that threshold to be declared as 0.05. Where a coated sheet sends most of what it receives back downwards, this face sends back only a fraction. The solution is also backed by laboratory tests, including a B-s1, d0 reaction to fire classification.

It remains to be seen what this gives under a real roof. An infrared thermometer, a shed, two readings a few centimetres apart: 54.6 °C on the underside of the sheet, 29.2 °C on the face of the R'BULL Pro 13 fitted beneath it.

This figure must be read for what it is: a one-off reading, taken on a given day under a given roof, not a standardised test. It still shows the only thing that matters for what lies below. It is no longer a surface at 54.6 °C radiating onto the animals, the pallets and the staff, but a surface at 29.2 °C. Twenty-five degrees less on the face that looks down at them. That is where the fight against heatwaves is won inside a building, and it is also what makes low-cost cooling possible, by reducing reliance on air conditioning.

Three practical arguments add to the figure, and they are often what decides on a building in operation: thirteen millimetres steal no usable height under a truss; a roll is handled by two people, with no machinery; fitting is done from below, without removing the covering. On an island destination, where freight is billed by volume, a forty-foot container carries about 4,000 m² of Pro 13. That is a distribution argument as much as a technical one.

What can be claimed, and on what basis, is worth setting out in black and white.

A clarification that matters, and one we prefer to give ourselves: none of these values makes a building compliant with anything. Directive 2007/43/EC, for example, requires the indoor temperature of a poultry house not to exceed the outdoor temperature measured in the shade by more than 3 °C once that temperature passes 30 °C, for farms above 33 kg/m². That requirement applies to the building, ventilation included. What the shield removes is the radiant load, the largest share on a clear day. The rest still depends on ventilation and management.

Fitting without stopping production

Fitting to the roof underside is the most common configuration on these sites, and the simplest: the insulation is fixed under the roof structure, without removing the covering and without stopping the building’s activity more than necessary. The sheets are laid perpendicular to the purlins, butted edge to edge, and fixed with a pneumatic nailer to the roof structure.

Two points make all the difference between a job that delivers and a disappointing one. The first is the air gap: reflective insulation pressed against the sheet loses most of its value, since there is no longer a space for the radiation to cross. The second is continuity, at the verges, at the ridges, around rooflights and duct penetrations, wherever an opening locally brings back the conditions of a bare underside.

The mistakes that cost the gain

• fitting the insulation against the covering, with no air gap on at least one side;
• leaving sheets apart at the verges, where nobody ever looks;
• forgetting technical penetrations, extractors, downpipes, cable trays;
• expecting the insulation to meet an indoor climate requirement on its own, when ventilation is part of it too;
• reusing a thermal resistance obtained with vertical air gaps to justify a roof, when the configuration is not the same.

In French buildings open to the public, there is an extra constraint. Article AM 8 of the French fire safety regulation covers any insulation thicker than 5 mm and leaves two routes, a classification of at least A2-s2, d0 or a thermal screen on the inner fire side. Since R'BULL Pro 13 is classified B-s1, d0, it falls under the second route, as explained in our article on thin insulation in public buildings.

Livestock buildings and cities turning into heat boilers

The mechanism does not care about sectors. In a logistics warehouse, radiation coming down from the roof builds up high and falls back onto the racking: it damages whatever is sensitive to temperature, it wears down forklift drivers, and it keeps refrigeration units running that were never meant to make up for a roof. In a retail outlet, it is paid for in air conditioning. In a research centre or an instrument room, it is paid for in measurement drift. The same containers leave for all of these sites.

In the tropics, the case has already been made to the authorities: in the French overseas departments, the RTAA DOM sets a solar factor of no more than 0.03 for roofs, and the two build-ups calculated by the LNE with an R'BULL Pro 13 under white sheeting meet that threshold. The calculation is redone for the roof actually built, as explained in our article insulating an overseas roof.

That is the thread Ceilingo follows internationally: insulation designed against radiant heat gains, to limit the impact of heatwaves and reduce the boiler effect in homes and cities. The cycle is well known. Heat gets in, people switch on the air conditioning, the air conditioning dumps its heat outside, the street warms up, people use even more air conditioning, and some cities now exceed 50 °C. Every watt of radiation stopped at the roof is a watt no machine will have to dump into the street.

On a livestock building as on a warehouse, the right way to start is always the same: describe the existing roof, say what is underneath and at what temperature it has to stay. Our technical support reviews the proposed build-up and supplies the input data for the calculation; the reports quoted here can be read in full on the test reports page, the complete range is in the reflective insulation section, and new market projects go through our distributors.