The invisible building material

Introduction

Eva Geering, Andrea DepIazes

Inside

Fig. 1: Multi-layer wall construction

Temperature gradient within the layers

Fig. 1: Multi-layer wall construction

Temperature gradient within the layers

Of concealment and exposure

The "multi-layer wall construction", designed to satisfy the thermal performance requirements of a building, grew out of the oil crisis of the 1970s and the subsequent realisation that we must reduce our consumption of energy. The outermost layer in our wall - now resolved into layers - serves to protect the (usually) unstable i nsulation from the weather. The i nsulation in turn (usually) encloses the i oadbearing structure for the whole building, to which it is fixed, like a wool coat. This technically obvious development raised new questions related to the architecture: What does an insulated wall look like? Could or should its form correspond to that of a monolithic wall? One obvious solution to this dilemma is to build the outer protective layer in the form of a self-supporting leaf of masonry or concrete. That enables our multi-layer wall to appear like a solid wall, almost as if there had never been an oil crisis. Even if the i nsulation is protected only by a thin layer of render in order to reduce the amount of work, our wall still appears to be a solid structure. At least so long as we do not actually touch it... Systems with ventilation cavities avoid these pretences and convey a more lightweight yet protective appearance, with a cladding of wood, sheet metal or slates. This arrangement also covers the inevitable layer of i nsulation and uses it only indirectly as a reason for altering the architecture. It is hardly surprising that in the 1970s, in contrast to the dogmas of Modernism, architecture again became a medium with meaning, and the clothing theory of Gottfried Semper again became topical.

In their Suva Building in Basel, Herzog & de Meuron pursued a strategy contrary to the concealment theory. As the insulation is protected by a transparent, glass skin, we get to see materials that were not actually intended to be visible. Although during the age of Modernism all decoration was renounced and the "truth of construction" proclaimed, revealing the i nsulation material in this instance is not concerned with a didactic derivation of constructional details. Instead, what we have here is the breaking of a taboo and the fascination with "ugly" materials. In particular, the use of unconventional materials raises probing questions of cultural conventions and reveals the beauty of their shabbiness. The tension between meaning and effect results in a poetry of the material: "How is poetry revealed? It is revealed by the fact that a word is recognised as a word and not as a mere substitute for something it designates." (Roman Jakobson, Questions de poétique)

Heat losses versus heat gains

Insulation protects against heat losses from the inside, but also against an excess of heat entering from the outside. One or the other of these effects is relevant depending on the climate; in the temperate climate of continental Europe preserving heat and gaining heat are desirable, depending on the season. One attempt to deal with this paradox that is intrinsic to materials is the development of transparent thermal insulation. This type of i nsulation, comprising several components, does not block out the light and hence heat but rather allows it to penetrate and heat up a wall capable of storing this energy. Transparent thermal i nsulation is not only permeable to light and heat but is also transparent to visible light. This is especially obvious in the direct gain system in which the transparent thermal i nsulation is employed as an enclosing element without any wall behind it. The use of transparent thermal insulation in this way is similar to the use of a not completely transparent window. Not only the outer protective layer of this wall construction is transparent, as we can see on the Suva Building, the insulation itself is virtually invisible. It is, so to speak, non-existent and permits the illusion of being reckless with the building performance parameters (see "Transparent thermal insulating materials", p. 145).

Synthetic building materials

Whether visible or invisible, the forms of thermal i nsula-tion mentioned above are part of an elaborate system of complementary and interdependent layers.

Synthetic building materials such as masonry or concrete with insulating properties satisfy the desire for simple buildability. In the meantime, industry can offer a wide variety of building materials that provide both loadbearing and insulating functions. The key physical and structural

Fig. 2: Existing and new buildings linked by insulating glass facade; top: straight on the road side; bottom: diagonally in the inner courtyard

Herzog & de Meuron: Suva combined residential and commercial development Basel (CH), 1988-93

Fig. 2: Existing and new buildings linked by insulating glass facade; top: straight on the road side; bottom: diagonally in the inner courtyard

Herzog & de Meuron: Suva combined residential and commercial development Basel (CH), 1988-93

Outside

Inside issue is to be found in this duality. The loadbearing material is so permeated with air-filled pores that it just exhibits sufficient load-carrying capacity, while the air captured in the pores, with its poor conduction, provides an insulating effect. So the insulating function always weakens the loadbearing material, with the ratio of strength to i nsula-tion needing to be determined in each case. The blurred dividing line between a loadbearing material with insulating properties and a loadbearing insulation material characterises such materials. Synthetic building materials, especially porous and brittle insulating masonry units, call for careful workmanship on site and must always be protected against moisture. In order to guarantee the required protection from the weather, synthetic building materials must be rendered or treated with a water repellent.

Polyurethane as a loadbearing shell

Another strategy comes to the fore in the example described below. The i nsulation is no longer applied to the loadbearing layer, nor does it imply it; instead, the layer of insulation is the loadbearing layer.

Rigid insulating materials with a good compressive strength have been developed for insulating components subjected to compression loads, e.g. flat roofs or parking decks for heavy-goods vehicles. Philip Johnson exploited this technical development for the architecture of Gate House in New Canaan (Massachusetts, USA).

Gate House (a visitors' pavilion for Johnson's "Glass House") was erected using a complementary method with the help of conventional materials: i nsulation, concrete, reinforcement. However, their interaction is not easy to decipher. The components do not simply complement each other in the finished building nor are they completely fused. The reinforced layer of insulation functions as permanent formwork for a thin strengthening and protective layer of concrete. The method of construction

Fig. 3: Sketches of wall construction (horizontal sections) Top: the rigid PU foam insulation between two layers of reinforcing mesh serves as permanent formwork. Bottom: rigid PU foam insulation panel covered with two coats of sprayed concrete both sides

Philip Johnson: Gate House, New Canaan (USA), 1995

Fig. 3: Sketches of wall construction (horizontal sections) Top: the rigid PU foam insulation between two layers of reinforcing mesh serves as permanent formwork. Bottom: rigid PU foam insulation panel covered with two coats of sprayed concrete both sides

Philip Johnson: Gate House, New Canaan (USA), 1995

used at Gate House is based on an Italian patent which Johnson's structural engineer, Ysrael A. Seinuk, brought to his attention. Normally, this method of construction - in the form of panels made from two parallel layers of reinforcing mesh and an intervening layer of i nsulation (rigid polyurethane foam), the whole covered with a thin layer of sprayed concrete - is used to construct cheap housing. Unlike conventional concreting no f ormwork is required. In order to erect the complex shapes required at Gate House the horizontal sections through the building were built as wooden templates and positioned with the help of a scaffold.

Using these as a guide, similar to the construction lines on a drawing, the building was assembled from the prefabricated rigid foam panels. The partly flat, partly convex, partly concave parts were joined together on site like the pieces of a puzzle. At this point the shape of the building could still be changed, a fact that Johnson made full use of; the opening for the door was cut out, the surfaces and edges given the correct form. The first layer of sprayed concrete stiffened the assembly of panels and enabled most of the templates and the scaffold to be removed. The second layer of concrete gave the wall the necessary thickness and provided the necessary cover to the reinforcement. The outcome of this reversal, in which the formwork is suddenly on the inside, is an apparently monolithic, thin-wall concrete shell. This method of construction in which the design can be manipulated during the building process renders possible the dream of plastically deformable, insulated concrete.

Walls of straw

Straw is a pure i nsulating material. However, if you compress it, it can become a loadbearing material. Here again, it is the enclosed pockets of air, not the straw itself, that create the insulating effect. The development of straw bale presses began around 1800 in the USA. In those regions in which grains and cereals were cultivated the fields were literally covered in "oversized roofing tiles" following the harvest. It didn't take much fantasy to turn these elements into temporary shelters.

It transpired that these temporary buildings outlived their planned period of usefulness completely unscathed, indeed even thwarted the extreme summer and winter conditions of Nebraska, and that a comfortable climate prevailed inside throughout the year.

Today, this old strategy is gaining favour again, albeit in the guise of sustainable building, e.g. Tscheppa House in Disentis (GR) by Werner Schmidt. In order to prevent moisture problems, a concrete foundation is cast on which the bales of straw and the timber reveals to the openings are built. The bales of straw are assembled in a brick-like bond. Vertical straps, which have to be retightened several times during the brief period of erection, draw the straw

3 Finished assembly of rigid foam panels 4 Cut-out for large entrance opening (note the difference between this and photo 3)

Edges reinforced with additional bars.

Fig. 4: Progress on site

Philip Johnson: Gate House, New Canaan (USA), 1995

5 Building coated with the first layer of sprayed concrete 6 Gate House cleaned and prepared ready for painting

Fig. 4: Progress on site

Philip Johnson: Gate House, New Canaan (USA), 1995

1 Reveals to openings mounted on concrete foundation; first course of straw bales In position

Fig. 5: Progress on site

Werner Schmidt: Tscheppa House, Disentis (GR), 2002

3 Positioning the intermediate timber layer to act as a bearing for the floor anc reveals of the upper storey; the vertical strapping is readily visible here

Fig. 5: Progress on site

Werner Schmidt: Tscheppa House, Disentis (GR), 2002

4 Structural shell almost complete, only the protective layer of render has yet to be applied

Fig. 6: Built from bales of straw

Slmonton House In Purdum, Nebraska (USA), 1908

Fig. 6: Built from bales of straw

Slmonton House In Purdum, Nebraska (USA), 1908

bales tightly together and hence consolidate the walls to such an extent that even two-storey buildings are quite possible. Intermediate timber boards serve as bearings for the joists, beams and reveals of the upper storey. Once the straw house has finally settled, it can be r endered and hence protected from the ravages of the weather. Therefore, the inevitable form of construction results in a building with metre-thick, sculpted walls. The straw wall seems, quite by chance, to solve the dilemma sparked by the oil crisis. What initially began as an ecological experiment, could lead to a new architectural style of "Baroque plasticity". The game has begun.

Further reading

- Gottfried Semper: Style: Style In the Technical and Tectonic Aits; Or Practical Aesthetics, Harry Francis Mallgrave (ed.), Los Angeles, 2004

- Martin Steinmann: De Unterwäsche von Madonna, lecture, 1996 published within the scope of the Alcopor Award 2000.

- Roman Jakobson: Questions de poétique, Paris, 1973. English translation: Romar Jakobsen: On Language, Harvard, 1995.

- Jeffrey Kipnis, Philip Johnson: Architectural Monographs No. 44, London, 1996

- Herbert Gruber and Astrid Gruber: Bauen mit Stroh, Staufen, 2000.

- Die Südostschweiz., "Im Stroh schlafen", 27. 11. 2002, p. 19.

Properties of materials

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