Cool roofing: reflective roof coatings to be handled with care

How to measure the effectiveness of cool roofing? What precautions should be taken during maintenance? What about companies' responsibilities?

"Cool roofing" is a method that uses reflective coatings (waterproofing systems or specific paints) to reduce the heat absorbed by roofs, offering a passive solution for cooling buildings during the hottest months. This technique requires careful installation and regular maintenance to guarantee its performance. Reflective paints require particular attention in terms of compatibility and durability, and their application must be assessed carefully to avoid negative impacts. Poor material compatibility can lead to insufficient adhesion, cracking or delamination, which can compromise the watertightness of the roof...

"One very important concept in tackling the subject of reflective paints is relative to "common techniques", which are defined by reference systems, versus "non-common techniques", which do not have a reference system recognised by the construction industry. For SMABTP, which follows the AQC flow chart, a technique is standard if it meets three criteria", explains Stéphane Orsetti, head of construction prevention at SMABTP: the existence of a product standard (e.g. NF EN 1062-1 for paint and decorative coatings), the existence of an application standard, and compliance with the suitability for use of the processes and their areas of application.

Albedo and reflectance index

The effectiveness of a cool roofing coating is measured by its albedo, which indicates its ability to reflect sunlight, and by the solar reflectance index (SRI), which assesses its ability to stay cool. Products on the market have evolved, offering innovative compositions such as silica aerogel for insulation or oyster shell powder for easier recycling. It should be noted that the performance of materials can be compromised by soiling, and certain precautions must be taken to avoid degradation of the reflective coating.

Maintenance and cleaning

Reflective coatings applied to roofs require regular maintenance to maintain their performance. The build-up of dirt and debris can reduce the albedo of the coating, diminishing its ability to reflect sunlight and prevent heat build-up. Regular, scheduled maintenance is therefore essential to maintain the benefits of cool roofing. To avoid potential problems, it is strongly recommended that you keep a close eye on any special points such as junctions, edges, etc., which are considered vulnerable areas and could be sources of infiltration. Here again, damage to these areas can compromise the watertight integrity of the roof.

What responsibility do companies have?

Reflective paints are for aesthetic purposes only. They are not waterproofing. They have no waterproofing function and are therefore not covered by the ten-year guarantee. Another point is that there is no guarantee that they will function properly. On the other hand, as far as the obligation to achieve results is concerned, the company may be held liable under ordinary contract law for poorly executed painting work.

To sum up, any substrate not recognised by the NF DTU means that the work is considered to be using a non-standard technique. The field of application must be respected, and the company must declare the use of a non-routine technique to its insurer, or risk being denied cover or being subject to proportional compensation rules. For Stéphane Osetti of SMABTP, "another risk with these products is that they may alter the B ROOF (t3) fire resistance classification of the flat roof by increasing the combustible mass that can be mobilised on the structure when the paint is applied. That's a lot of unknowns, and there isn't enough hindsight".