Installation of very light thermal insulation with a rendering on a new facade can in principle be done with an adhesive. However, most people don’t trust this because it depends on the state of the facade (wet by rain, contamination due to traffic, etc.). At that moment, they want mechanical fixings, which are anchored in the facade.

In case of a ventilated surface with more heavy thermal insualtion like cellular glass and with a heavy cladding, an improved mechanical fixing is needed.The patent of Willy Trittenbach, once a collegue is a nice example of such a very stable fixings. But stainless steel has thermal conductivity of 15 W/mK and GLAPOR cellular glass about 0.05 W/mK or a factor 300. This means that a 6mm screw cinducts the same amount of heat as a cylinder GLAPOR cellular glass with a diameter of 100 mm, which is a huge cold bridge. Besides the screw, also the legs are passing the cellular glass. The patents mention at least one fixing in every boards 450 x 600 or a cold bridge of about 10% of the thermal insulation. To remove this cold bridge, a new patent was taken.

This new patent eliminates works with a double layer insulation, separated by a board, which is fixed on the walls. In this case, there is no direct connection by a long screw between the surface of the thermal insulation and the wall.

However, in Germany ventilated facades have to be insulated with thermal insulation with melting point above 1000°C according to DIN 4102-17. Check the German product datasheet before ordering the thermal insulation in case of Germany.

In 2022, it is 90 years ago that Professor Ilya I. Kitaygorodsky presented cellular glass at the All-Union conference on standardization and production of new materials in Moscow. Therefore, BELGLAS BV conducted some research about this man, with which we share a common respect for cellular glass.

Professor Isaak Ilyich Kitaygorodskiy was the founder of the Department of Chemical Technology of Glass and Sitals at the D. Mendeleev University of Chemical Technology of Russia. In the following, I copy a part of an interview with Vladimir Nikolaevich Sigayev.

The Department of Glass is a legendary one. It was founded almost 90 years ago, in 1932, by the famous Soviet scientist, technologist #1 in the field of glass, Isaak Ilyich Kitaygorodskiy. Suffice it to mention that the ruby stars of the Moscow Kremlin were created on the basis of his developments related to glass coloring processes. I should remind you that the towers of the Kremlin were originally decorated with two-headed eagles. The builders of communism got to them only in 1937, and the eagles were replaced by metallic stars, which, however, were not visible at night and did not make a good impression at all. Therefore, it was decided to replace them by ruby-colored glass stars which fitted perfectly well into the architectural appearance of the Kremlin. It was a very beautiful design that complemented the brilliant work of Aristotle Fioravanti. 

Let us return to the foundation of the department. 1932 was a landmark year not only in the context of its founding. It was the same year when the famous article by William Zachariasen, the largest scientist of crystal chemistry, who laid the foundation for the theory of the glassy state structure, was published. By the way, this two-page work remains the most cited article in glass science to date. 

Kitaygorodsky, the founder of the department, worked as a chief engineer at a glasswork in Zaprudna near Moscow before the events of the 1917 revolution. Kitaygorodsky set up the production of light bulbs at this, judging by the preserved photographs, quite ruined facility. In fact, as they say today, he started the process of import substitution, and beginning from 1913 Russia has been using domestic light bulbs. After 1917, when the entire country was electrified under the GOELRO plan, they began to be called “Ilyich bulbs,” referring not to Isaac Ilyich, but to Vladimir Ilyich, which I find a major historical injustice. 

Later, the activity of the department covered all the variety of glass technologies, including all the new challenges coming from the needs of instrumentation, medicine, and ecology. The main challenge was related to the improvement of sheet glass and organization of its multitonnage production (95% of all glass production is oriented on the creation of window sheet glass, i.e., glass used in architecture). The problem of sheet glass production was finally resolved with the aid of the so-called float technology, which makes it possible to obtain nearly perfect glass sheets up to six meters wide by melting the glass mass into liquid tin. In Russia, this problem has been solved when foreign companies came to the Russian market such as “AGC,” “Guardian,” “Pilkington,” etc. It is difficult to overestimate the contribution of Kitaygorodsky and his students in the development of sheet glass, electrovacuum, medical glass, foam glass, and seals.

Today, a lot of research about cellular glass is again performed in Russia. I guess that our spiritual father will be pleased.

The inverted roof has the thermal insulation on the waterproofing membrane. A better but less known name is the Protected Membrane Roof (PMR). Another contraction was IRMA (Inverted Roof Membrane Assembly), which was once a registered trademark of the Dow Chemical Company. Moreover, Dow Chemcial company had once a patent on the inverted roof. It was filed in 1965, which means that there was no absolute freedom to install this type of roof in the USA untill 1985.

The patent describes that the thermal insulation has to be watertight and should not absorb humidity. It is a surprise that this patent showed up 24 yeasr after the invention of the XPS. The patent mentions also cellular glass in its introduction: The thermal insulating layer, employed in the practice of the present invention, beneficially is a closed cellular material which is substantially water impermeable. Particularly beneficial and advantageous, for use in the pres ent invention, are cellular plastic foams of a closed cell configuration including styrene polymer foams, styrene acrylonitrile copolymer foams, styrene-methylmethacry late copolymer foams, polyvinyl chloride foams, poly ethylene foams and other water impermeable materials available in cellular foam form which are well known to the art. Foam glass is particularly advantageous when it is desired to omit a protective layer over the thermal in sulating material. A protective layer beneficially is employed when synthetic resinous organic cellular thermal insulating layers are utilized. Such organic materials are generally subjected to decomposition when exposed to weather and more particularly when exposed to Sunlight.

Cellular glass can not be used in freezing countries because freezing water in the open cells on the top surface will induce cracking and water absorption. For that reason, cellular glass was only used under the water proofing membrane like shown in the many applications of GLAPOR cellular glass. However, if your are able to solve the problem of open cells at the surface of cellular glass, the way is open to use cellular glass in an inverted roof. The advantages in these sustainable times are clear.

Since less than one year, a patent was published, which claims to solve this problem. This patent from a Belgian inventor works with a mineral protective coating on the cellular glass surface.

This patent does not refer to the original inverted roof patent but is on the other hand very extended. It describes a few detailed methods how to prepare a mineral protective coating on the cellular glass. All these coatings are based on alkali silicate solutions with mineral fillers and even some testing in a climatic chamber for facades is included. The coating is proven to be resistant to UV, higher temperatures and freezing water. I guess that a mineral coating, based on hydraulic lime could also be suited. I used it once for a “sculpture” and it survives already 15 years in a Belgian climate, even the horizontal part.

Choosing between a warm roof (thermal insualtion under the water proofing membrane) or an inverted roof is choosing between the risk for damage / wear at the thermal insulation or damage / wear of the water proofing membrane. I guess that the second risk is at least more acute. An inverted roof needs ballast on the thermal insulation, which makes the roof construction more expensive. But Germany is going in the direction to make ballast on the water proofing membrane an obligation for every flat roof.

If the roof construction can bear ballast and cellular glass with a mineral coating is available, an inverted roof with loose-laid cellular glass is the most durable solution. Indeed, the life time of the membrane will be very long (no UV, stable temperature and no mechanical damage) and recycling at the end of the roof life (building life) will be much easier. These coated cellular glass blocks can be found at Hytherm CG and I guess other suppliers of cellular glass will follow. In the UK, non-combustible thermal insulation is an issue since the incident with the Grenfell Tower, while the inverted roof with the combustible XPS was very popular there. Mineral coated cellular glass is there a big opportunity today.

In my opinion: “The warm roof is dead, hurray the inverted roof”

In the mean time, we learn the above patent has been aborted.