Le Corbusier: a French lesson on 'Murs neutralisants'

Is there still anything to discover about Corbu? Hidden inside his extensive writings - and sometimes evident in his projects - Le Corbusier seems to have individuated five building-physic concepts, were these his own developments or not:

• natural ventilation (aération naturelle)
• natural lighting (éclairage solaire)
• solar control (brise soleil)
• thermally active facade in opaque or glazed walls (mur neutralisant)
• internal air conditioning (respiration exacte)

These made for him part of "the modern techniques" (les techniques modernes). Funny they are precisely five points - but this is a coincidence...

Sections showing sun lighting at the Zurich Sanatorium (left) and the skyscraper of Quartier La Marine (right). LC Ouvre Complete 1946-1952.

Ventilation scheme in standard houses for workers. Le Corbusier.

Corbu seems to have always paid attention to the first two items: natural ventilation and natural lighting, be it at his writings and in his projects (the images above are a good example). He was influenced by and a promoter of the hygienist culture of his time in architecture. But in the other three points he went beyond the usual and became the first modern architect really interested in mixing passive and active methods of energy control. Regardless the accuracy of his concepts from a physical point of view, this is a remarcable feat.

Seen from today's distance, Le Corbu was a prophet not only in architectural language and urbanism but also in identifying the importance of a right combination between building design (passive measures, mass, ventilation etc) and active systems (air control and mechanical distribution) for achieving comfort in buildings. But his strength as prophet may be precisely in his weaknesses as master builder. Had Le Corbusier had a rigurous technical knowledge in the five points above, his predictions would not have been as telling for the coming generations as they were.

The two active concepts - the latter of the five, which Corbu developed between 1926 and 1933 - were the 'Mur neutralisant' and the 'Respiration exacte'. In my opinion, Corbu had it clear that both were intended to work together because they were complementary. Corbu tried to implement them at the Cité de Refuge in Paris and the Centrosoyuz in Moscow, unsuccessfully in both cases. Put simply, his intention was to obtain an internal comfortable environment all year round and in all climates.

Corbu coined two names but in fact three aspects were required simultaneously:

1. A very high air-tightness through the envelopes - hence the idea of sealed glass (or sealed opaque walls) being part of the 'Mur neutralisant' concept. The intention was -rightly - to avoid air and heat flowing from inside to outside and viceversa.
2. A mechanical system of controlled ventilation capable of adjusting both air temperature and humidity - that is, a rough description of an air conditioning system. This was the idea behind the 'Respiration exacte', which in fact comes from his colleague the engineer Gustave Lyon.
3. Finally, in order to allow glazed facades to act as external thermal envelopes, an active device that neutralized energy flows (both in winter and in summer) through glazed surfaces: the 'Mur neutralisant'. This acted mainly as a barrier avoiding heat to flow inside-out during winter and outside-in during summer. Corbu delevoped an existing, earlier device (water heat radiators installed between two parallel glazed walls) into a more ambitious idea. By inserting air pipes around a sealed double glazed cavity he suggested that treated air could be blowed, warm in winter and cold in summer, so as to neutralize the outer conditions. This would allow the 'Respiration exact' system to maintain a constant internal temperature of 18ºC.

Respiration exacte and Mur neutralisant as they were envisaged for the Centrosoyuz project in Moscow

'Mur neutralisant'  and 'Respiration exacte' diagram, 1929, as published in 'Précisions'

 Where did these ideas come from? Were they revolutionary or not? The 'Respiration exacte' concept seems to be a somewhat poetic version of the mechanical ventilation system used by Gustave Lyon at the Pleyel Theatre and in other French auditoria. It seems that Lyon called his system 'Aération ponctuelle', not so different from 'Respiration exacte'. In his drawings (see below) for the Centrosoyuz project in Moscow Corbu used the engineer's name in some of the details: "Aération ponctuelle. 80 litres-minute d'air à 18ºC par personne avec régénération dans circuit fermé; système Gust. Lyon" (Point ventilation. 80 litres/minute of air at 18ºC per person with regeneration in closed circuit; system Gust. Lyon).


Image of the Centrosoyuz project for Moscow with references to the Mur Neutralisant and the Aération Ponctuelle (1928)


Lyon himself was not a mechanical engineer but an specialist in acoustics - to be precise, an expert in piano sound and its mechanisms. It seems that he entered the area of mechanical ventilation after having designed the acoustics for many concert halls, and probably having experienced the discomfort of those closed unventilated spaces. But he was not a climate engineer as Willis Carrier or the men at the American Blower Company. His intuitions on air conditioning came from his practical experience at improving the ventilation of the Salle Pleyel or the Trocadero Palace after he had gained reputation as an acustician. Lyon was 70 years old in 1927 at the opening of the Salle Pleyel in Paris: not exactly an eager engineer in contact with the novelties from New York or Chicago. In any case, the idea of an enclosed inner space - sealed from the outside - with some mechanical devices to control air temperature and humidity was not new, and it could very well be passed from Monsieur Lyon to his young new client, l'architecte Charles Eduard Jeanneret (Corbu).

Centrosoyuz plan and external view. Notice the double glazed wall with sliding windows.

In relation to the 'Mur neutralisant', I fully agree with Reyner Banham's position at his legendary book "The architecture of the well-tempered environment". Le Corbusier had experienced a similar concept for the windows in his Villa Schwob in Switzerland by 1916, so that this seems to be his own development. In the Ville Schwob very large windows (one of them two storeys high, see below) were designed in two layers, with heating pipes between them, to prevent down draughts. In t he same details for the Centrosoyuz (1929) he referred to them as "Murs neutralisants de verre ou de pierre; circuit fermé rapide d'air sec chaud (hiver) ou froid (été); systéme L.C. - P.J." (Neutralising walls in glass or stone; quick closed circuit of dry hot air (winter) or cold (summer); system Le Corbusier - Pierre Jeanneret). The 'Mur neutralisant' was his baby; the 'Respiration exacte' was Lyon's.

Villa Schwob, La Chaux de Fonds 1916. Notice the large window pane above the garden entrance: this was a double glass with an intermediate radiator system.

The glass solution was typical to the other Corbu 'Mur neutralisant' schemes; that for the opaque walls in Centrosoyuz reveals another great Corbu's intuition. An enclosed air cavity between two walls of pink tufa stone from the Caucasus (a volcanic, porous stone) would have been a very adequate thermal solution for opaque walls in Moscow, even if there was no hot air circuits inside. The Russian client ultimately dismissed the 'Mur neutralisant' system because of the lack of technical justification. At least they kept the double glazed wall, of which there were some previous examples built in Moscow (see the images of Zuyev Workers Club right below, a project by Ilya Golosov finished in 1926).

The Zuyev Workers Club. Ilya Golosov, 1926. A precedent of double skin glazed walls in Moscow before the Centrosoyuz.

But the opaque wall as it was designed, even without blowed air in the cavity, would have been much better in terms of insulation than the one-layer stone wall finally built, with a thickness of 40cm.

Could these two concepts, the 'Mur neutralisant' and the 'Respiration exacte' really work? Were they logical? The answer depends on the system.

It is not clear to me what Le Corbusier meant by 'Respiration exacte' (I suspect it's not just me; Corbu was not an engineer and he did not describe the concept in depth). The Centrosoyuz drawings show a viable closed circuit distribution, a system which might have worked applying the knowledge in air conditioning already available at the time. Trying to keep the inner temperature at 18º all year round might be onerous in terms of energy consumption, but it was a good intention in terms of comfort. I don't see a real invention here but the application of an existing concept.

Model for the Centrosoyuz complex

In terms of viability the 'Mur neutralisant' is much more difficult to accept; not because it was ahead of its time but simply because it was not reasonable. The concept of a neutralising wall was tested and calculated by two independent companies at the time, one French and the other American. Both Saint Gobain after their twin-box test and the American Blower Company in their calculations concluded that such a system would require an enormous amount of energy to really make a difference on the inner temperature. And I agree without conducting any tests or calculations, because of two weaknesses: too large conductivity (heat in the cavity would scape out in winter) and no control of radiant heat (solar radiation would come in during summer). Let us see this in a bit more detail.

The Centrosoyuz after its opening. The main glazed walls are double glass walls but with no intermediate heating system.

First the conductivity issue: the air-filled cavity would quickly try to equalise its temperature with the outer one - because the temperature gap would usually be higher to the outside than to the inside of the room. A single glass pane has a very high thermal conductivity, meaning that the heat would flow out (in winter) and into the cavity (in summer) instead of warming or cooling (respectively) the air in the room adjacent to the inner side of the glass. The guys from Saint Gobain, who were surely aware of the patents in double glazing already taking place in America, suggested a better alternative: a double glazing on the outside layer instead of a simple glass. And today we would suggest an even better alternative: a triple glass with low emisivity coatings and argon-filled cavities without any active mechanism inside.

Views of Centrosoyuz today

But that would not be enough: we have to take care of the solar radiation, as Le Corbusier would learn the hard way at his Cité de Refuge for the Salvation Army in Paris, based on a project started in 1929 and finished in 1933. The story is well known. This is a text written by Le Corbusier defending his active air-handling principles for La Cité de Refuge in 1931:

“Our Invention, to stop the air at 18 degrees undergoing any external influence… These walls are envisaged in glass, stone, or mixed forms, consisting of a double membrane with a space of a few centimeters between them… a space that surrounds the building underneath, up the walls, over the roof terrace… 

Another thermal plant is installed for heating and cooling, two fans, one blowing, one sucking; another closed circuit… Result, we control things so that the surface of the interior membrane holds 18 degrees”

The South facade of the Cité de Refuge building right after completion in 1933 and as it is now, with the brise-soleils and the sliding windows.

In spite of his great selling capability, Corbu was able to implement only one third of his active principles in the Salvation Army building. The south-facing single glazed facade of 1,000m2 was completely air-tight (no opening windows), but the 'Mur neutralisant' and the 'Respiration exacte' were rejected due to budget constraints. The building remained rather warm during the opening winter, but it proved a complete failure the next summer. Corbu blaimed the absence of air conditioning - true but expensive for a building like this - while the occupants were just asking for opening windows to provide some natural ventilation.

Both (Corbu and his client) were partly right, although the final solution would only come as a consequence of the bombings in Paris. The facade was completely destroyed during the war and Le Corbusier received the commision for rebuilding it. This time, after his trips to Algeria, Argentina and Brazil he had the final answer to the actual problem: an external sun screen to control solar radiation, or 'brise-soleil' was added outside the glass layer. This concept, a passive measure unlike the other two, would become an integral part of Le Corbu's architecture until the end of his career.

The brise-soleil at its most after the War: the Unité d'Habitation in Marseille and sketches by LC on sun control.

How did these trials and errors influence Corbu's vision on architecture? In my opinion the failure of his two active systems, 'Mur neutralisant' and 'Respiration exacte' in Paris and in Moscow led him towards embracing passive control systems after 1935. His architecture becomes more massive, concrete walls take precedence over naked glass and the brise-soleil reigns over every opening. His assistants during the fifties - as Iannis Xenakis in Chandigarh - are better informed about climate control for human comfort. Texts as Victor Olgyay's 'Design with Climate' (1963) emerge partly as a reaction to the excesses of the International Style, but also partly in line with Le Corbusier's view of an architecture more in contact with earth and natural environment.

Bioclimatism, solar charts, wind blow control, ventilation, illumination, healthy spaces... all these terms define Le Corbusier's architectural production after the war until the end of his prolific career. Corbu's strong alignment with these concepts was clearly an invitation for younger generations of architects to act with diffidence in regards to mechanization of internal climate.

Le Corbusier's early intuition about a glazed 'Mur neutralisant' as a way to achieve a 'Respiration exacte' inside his buildings was not right. But he seemed to have learned the lesson, moved on and helped young architects to learn it as well. Others cannot say the same.

Le Corbusier sitting in front of the site for the Centrosoyuz Building in Moscow (March 1931)

Let me finish this post with a small present for Corbu-addicts. These are a few lines of a long letter written by Le Corbusier in 1932 (at the time of construction of the Centrosoyuz, which he calls the Palace)  to the Soviet Commissar of Enlightenment Anatolii Lunacharskii. The translation has been provided by Ross Wolfe, and the whole text of the letter can be found here. Corbu was asking this soviet politician for permission to organize a conference to present his architectural principles. And he was clever enough to sound 'scientific' and progressive in order to get a positive answer...

"In Moscow, I could — outside the Palace — publicly speak of the Radiant City, and explain where progress and the grand view have led us and shown to your country, which is the only one possessing the institutions that permit the realization of modernist programs.  The technical detail of the questions concerning:

architectural reform

the 24-hour solar day and its programme

the new techniques of exact respiration inside buildings (with the recent laboratory experiments at St.-Gobain) (the most pressing problem facing the USSR)

the problems which agriculture poses for the domestic economy

the soundproofing of homes

acoustics

Here are the truths, realities, the long-range items that are informed by the spirit of the five-year Plan — much more than certain restrictive methods, Malthusian and lacking imagination, which have been so warmly embraced in the USSR.

And if anyone wants, I could speak of proportion, of beauty, those things that are the driving forces of my life, because happiness is not possible without a sense of quality."

The solar cycle, LC 1954

It has taken me days to understand the meaning of 'the 24-hour solar day and its programmme' but it is the clue to this story. What Corbu meant by the 24-hour solar day is wonderfully depicted - and described - in the attached later sketch from 1954. Nothing to do with the 'Mur neutralisant', all the opposite.

What this letter tells us is that Le Corbusier was at the time of writing, as early as in 1932, already departing from the mechanistic world of the 'thermal machine' and opting for the order of solar profit, of solar control. A world where bureaucrats or budget constraints would not oppose his inventions any longer. A world where energy would come free and abundant, only requiring control, not production.

But his interest remained the same all around this mental process: the search of happiness through architecture. Because, as his final words resonate like a manifesto:

"happiness is not possible without a sense of quality..."