Flat roof pitched roof

Repercussions for the building envelope

1. Rain

Flat roof a) Waterproofing: The waterproofing and water run-off layer must exhibit, depending on the system, a minimum fall of between 1.5% (upside-down roof) and 3%. The waterproofing layer is generally the topmost layer or the seconc layer below any wearing course or protective layer. The exception is the upside-down roof, where the waterproofing layer is beneath the thermal i nsulation. In this case it must be assured that the i nsulating material is moisture-resistant (various systems available).

b) Drainage: Rainwater is drained to a downpipe or gulley outlet at the lowest point on the roof surface and then inside or outside the building to a soakaway or drainage system. The provision of an upstand (parapet) around the edge of the roof is intended to prevent water running over the edge of the roof and down the facade during periods of heavy rainfall. Such a parapet must be at least 12 cm high (measured from top of wearing course or protective layer to topmost component of parapet - e.g. top of sheet metal capping) and must be absolutely watertight (SIA 271).

Pitched roof a) In contrast to the flat roof, the water run-off layer on a pitched roof must be rainproof but need not be waterproof (e.g. thatched roof). The drainage of the water must take place via the uppermost layer, which can consist of sheet metal, clay/concrete roof tiles, stone, glass, etc. The pitch varies depending on the material. However, the pitch must always be steep enough to ensure that rainwater drains without ponding. The secondary waterproofing/covering layer functions as a temporary roof should the roof covering become damaged and also helps during severe weather.

b) Drainage: A gutter is essential along the edge of the roof (eaves); it can remain visible (external downpipe) or it can be incorporated in the edge of the roof (internal downpipe).

General a) Oversailing eaves and verges protect the wall-roof junction against rain. The joints between roof covering and wall are exposed to extreme conditions (hydrostatic pressure). Underneath the eaves/verge the resulting eddy that develops, however, generates a countercurrent and lowers the risk of water penetration.

b) The dimensions of roof gutters and the number of downpipes are calculated according to the area of roof and the quantity of precipitation expected.

2. Sunshine

Flat roof

Some waterproofing materials are vulnerable to ultraviolet radiation (e.c and protected by a layer of gravel or similar material.

bitumen sheeting) and must be covered

General

In a lightweight roof a "stuffy" climate (a build-up of heat below the roof) is prevented by the circulation of air \n the cavity, and in a heavyweight roof it is the mass of the loadbearing layer, which absorbs the heat, that prevents this problem.

Thermal ¡nsulatlor Vapour barrier Falls (drainage) Loadbearing layer

Fig. 45: Flat roof, warm deck, scale 1:20

Thermal ¡nsulatlor Vapour barrier Falls (drainage) Loadbearing layer

Fig. 45: Flat roof, warm deck, scale 1:20

3. Wind

Flat roof

Wind suction is primarily a problem on uncoated roofs because the roof covering is not weighted down by gravel or other similar materials. The roof covering must be fixed to the loadbearing layer at individual points. Parapets around the edge of the roof (not suitable for cold deck systems) reduce the wind suction on large areas. The outer protective layer also has the task of providing ballast (e.g. gravel, concrete flags) for the layers below.

Pitched roof

On roofs with overlapping elements wind suction can be a problem, depending on the pitch and the weight of the materials. Wooden shakes/shingles or thatch must always be securely fixed. Owing to their weight, tiles can usually be simply laid in place without fixing, but at pitches of 60° and more they must always include an additional mechanical fastener.

General

Lightweight roofs must always include an airtight membrane

4. Temperature

General

Standards stipulate the thermal resistance and hence the minimum thickness of the various constructions. The climatic conditions of Central Europe mean that a layer of I nsulation to the enclosing envelope of rooms designed for occupation is always necessary. The type of I nsulation and its position within the roof construction depend on the system chosen.

5. Vapour diffusion from inside to outside

General

It must be guaranteed that moisture is not introduced into the layer of I nsulation through saturation of the construction due to vapour diffusion from inside to outside. Many insulating materials are poor insulators when wet Saturation can be prevented by using concrete for the I oadbearing layer (vapour-tight), including a vapour barrier/ check on the warm side of the insulation, or employing moisture-resistant insulating materials.

6. Snow

Flat roof

A parapet around the periphery of the roof (min. 12 cm) prevents fallen snow from penetrating the roof edge detail and creates a reservoir for meltwater.

Pitched roof

Snowguards must be fitted to prevent snow sliding off the roof General

The loadbearing construction must be designed to carry a certain snow load depending on the pitch of the roof and the location/altitude of the site.

7. Mechanical damage

Flat roof

It is primarily the uncoated roof that is vulnerable to mechanical damage - also due to hail. On a bituminous warm deck it should be ensured that the protective layer of rounded gravel does not contain any sand because this provides nutrients for plants. The small roots of plants gradually penetrate the waterproofing and render it useless On an accessible upside-down roof the thermal insulation is especially sensitive to point loads

Aluminum Screen Enclosure Materials

Protective layer (roof covering) Water run-off layer

Vapour barrier

Loadbearing layer for vapour barrier (lining)

Loadbearing layer

Fig. 46: Pitched roof, ventilated sheet metal, scale 1:20

Protective layer (roof covering) Water run-off layer

Loadbearing layer for roof covering Ventilation cavity counter battens Secondary waterproofing/ covering layer Thermal insulation

Vapour barrier

Loadbearing layer for vapour barrier (lining)

Loadbearing layer

Fig. 46: Pitched roof, ventilated sheet metal, scale 1:20

For current Swiss and German standards on roof construction see www.sia.ch and www.bauregeln.de

Flights of fancy

Daniel Gut

Fig. 1: Giovanni Battista Piranesi: Carceri, plate VIII, 2nd ed., 1761

Introduction

The staircase as a multiplier of the horizontal plane

Space for human movement is practically limited to two dimensions because gravity pins us to the ground. Our bodies cannot explore the space overhead. Accordingly, our perception of the world takes on a horizontal orientation. Architecture has been drawing its conclusions from this for thousands of years and arranges the functions horizontally. The staircase is therefore one of the important inventions in the history of architecture because it offers us the chance to link conveniently the vertical multiplication of areas for human movement by dividing the difference in height into small units that human beings can negotiate.

Every staircase renders two fundamentally different, opposing movements possible. And not only in physical terms: ascending and descending are terms loaded with mythological and psychological meanings as well. In Christian mythology, for example, the connection between places of good and places of evil are given extra significance by using the word pairs above-below and light-dark. This has consequences for the psychological dimension of the terms ascending and descending. These opposites firmly anchored in the human mind have been transferred directly into the secular world. The stairway to Heaven has become a ladder of knowledge, a ladder of virtues; the higher position in the hierarchy is better; we ascend to the top league or descend into madness.

Fig. 2: Haus-Rucker-Co: Big Piano, 1972

Piranesi makes use of extravagant, enigmatic staircases in his architectural vision Careen in order to lend his gloomy spaces an element of psychophysical disunion. The stairs lead into the depths of the dungeons and symbolise a world out of balance.

Ascending and descending movements, in relation to moving in the horizontal plane, represent a change of rhythm which has subconscious psychological repercussions. In the slowing of the rhythm as we ascend our spirit tends to want to hurry ahead of our bodies, to tackle our destination, or rather our immediate future. The German language even has an everyday specific, stair-related word for this: Treppengedanke - a forethought; likewise a word for the opposite direction: Treppenwitz - an after-

thought - a thought that occurs to us only after starting to descend the stairs while our minds are still upstairs dwelling in our immediate past.

Fig. 3: Eadweard Muybridge: Human and Animal Locomotion, 1887

Human beings have become accustomed to the artificial character of a succession of horizontal planes. Every child, having mastered the art of walking, then has to deal with climbing stairs. Over the years this motion becomes a programmed movement mechanism. But because this ritualised sequence of movements, in contrast to moving on a horizontal plane, is inextricably linked with the geometry of the step, the staircase enjoys increased attention. What this means for the architect is a chance to use materials to satisfy this enhanced focus. Apart from the fact that the architect can determine the rhythm of future movements by choosing a particular step geometry, he or she knows that the floor covering will be trodden upon with just a touch more care and awareness, that the handrail will be consciously perceived and that a rotational movement into the prescribed direction will take place on any landings necessary.

In the following I shall use word pairs to represent the contradictory characters or design concepts for stairs to demonstrate the potential opportunities and consequences of architectural decisions. The choice of these word pairs is intentionally arbitrary. The vista of possible options is too broad to want to cover everything.

The generating component of a project or building

Vertical access can be coupled with the three-dimensional concept of a building to the extent that it forms a permanent component or even the pretext for the concept. It is therefore an early topic in the design process and can be anchored in the design task. The design and choice of materials for vertical access are derived directly from the structure of the building or form a permanent component in this. Removal or repositioning during the ongoing design process becomes ever more difficult and practically impossible in an existing building without changing or destroying the entire concept. The enhanced potential for spatial quality is paid for by a loss of flexibility and is

Fig. 5: Frank Lloyd Wright: Guggenheim Museum, New York (USA), 1959

Fig. 6: Adalberto Libera, Curzlo Malaparte: Casa Malaparte, Capri (I), 1941

Fig. 5: Frank Lloyd Wright: Guggenheim Museum, New York (USA), 1959

or less complementary cnaracter, aepenaing on wnetner they have been devised as an accent, as part of a composition of various elements, or as a continuation of the building structure. In comparison to the aforementioned stairs they appear later in the design process. Their positioning and architectural expression are allowed much more flexibility. This applies to the design process and also to later changes to the existing building although, of course, the strategic positioning of a staircase remains crucial. The permanence within the building provides potential for a deliberate, relatively independent architectural statement which, in turn, can permit a fusion with the surroundings in numerous ways.

One example of this approach can be seen in the entrances to St Jakob Park - trunk-like staircase "hoppers" which, like mobile steps for aircraft passengers, are appended to the facade. The logic of the resulting flexible positioning could be adapted to suit the functional requirements. In terms of the materials employed, however, the translucent cladding to the staircase entrances ensures integration into the theme of the facade with its transparent plastic "rooflight" elements, which the nighttime illumination changes into a shimmering skin.

On the other hand, the spiral staircase in Le Corbusi-er's maisonette apartment is inserted like an artefact into the plan layout. Hidden in the base is the staircase leading down to the floor below. The permanence is expressed in the materials. While the strings blend in with the plastered surfaces of the apartment, the flight itself appears to be part of a composition of inserted elements.

Fig. 6: Adalberto Libera, Curzlo Malaparte: Casa Malaparte, Capri (I), 1941

Staircase as event or staircase as obstacle

There are stairs that invite the observer to use them. But there are others that we pass without noticing, and if forced to use them we get the feeling of being unwanted guests. One critical factor here appears to be the change in the degree of openness upon starting to use the stair or stair shaft. If this openness remains unaffected or is enhanced when using the stair, the stair tends to gain a more public character. The stair becomes an event. Numerous measures can be employed to manipulate this impression. The effective mass of the stair and its relationship with the surrounding space play a role. Three-dimensional settings can be devised in order to turn the ascent into a sensation or a social occasion. A dignified design and expensive materials can (but need not) emphasise the event of ascending the stairs.

Spatial and organisational decisions have turned the main staircase at the public library in Viipuri into an event. Visitors are initially channelled up a narrow stair before arriving at a broad landing in the very centre of the library. Although the handrail steers the visitor directly to the upper level, he or she senses the spatial extent of the symmetrical staircase on the central axis of the interior. The skill with which the handrail has been incorporated turns this stair into a combination of entrance and means of internal circulation, creates a prestigious staircase occupying the middle of the building.

Fig. 7: Herzog & de Meuron: St Jakob Park, Basel (CH), 2001
Fig. 8: Harbour steps in St Augustine (USA)
Fig. 9: Alvaro Siza: House of Dr A. Duarte, Ovar (E), 1985

In Balthasar Neumann's proposal for the Hofburg Palace in Vienna the ascent of the stair is celebrated as a primary spatial attraction. This monumental staircase is accommodated in the largest room in the Hofburg Palace and is located in a prominent position on the central axis of the complex, lit from the two courtyards at the sides. Starting at entrance level, two flights lead up into the great staircase hall where several flights and landings branch off almost like a labyrinth. This almost intimidating staircase seems to symbolise the feudal claims to power.

Just as interesting is the question regarding the opposite situation: How do we prevent a passer-by from ascending a stair? How do we express, with architectural means, that a stair is not to be used? Reducing the degree of openness to a more private character, or providing spatial or geometrical restrictions, turns the stair into an obstacle. The more abrupt this change, the more obvious this statement becomes. In addition, the architectural expression of the stair can help it to be overlooked or create an off-putting effect. Steep steps or the omission of safety features (balustrade) can enhance this impression. A similar effect can be created by embedding the stair construction "incidentally" into its surroundings and using the same materials, especially if this homogenisation presents a contrast to the more public space.

The photograph of the harbour steps in St Augustine (Fig. 8) shows quite clearly that this is not a descent for public use, that it is reserved for fishermen and sailors who need to reach their boats. The clarity of this architectural statement is the result of the abrupt change in scale between the expansiveness of the quayside and the confinement of the steps, promoted by the choice of material for the steps - the same sandstone as the quay wall.

In the house of Dr Avelino Duarte, Alvaro Siza employs nuance-filled means for the stairs leading to the private area of the house to indicate that the stair transcends a barrier to the more private living quarters. While the bottom steps, belonging to the half-public room, appear

Fig. 10: Balthasar Neumann: Proposal for the Hofburg Palace in Vienna (A), 1747

to be cut out of the material of the high plinth, the floor covering to the stair itself, a warm wood, together with a narrowing of the width draws a clear line between public and private.

Three-dimensional spatial fabric or stair core

Stair cores wind upwards over any number of storeys while their plan area remains equal or similar. They are usually quasi-autonomous shafts within buildings which join, or separate, the individual floors. Although the extent of the spatial separation can be manipulated by the type of connection between the stair shaft and the individual

Fig. 11: Alvar Aalto: Public library, Viipuri (FIN, today RUS), 1935

Fig. 10: Balthasar Neumann: Proposal for the Hofburg Palace in Vienna (A), 1747

Fig. 11: Alvar Aalto: Public library, Viipuri (FIN, today RUS), 1935

floors, or the vertical spatial "transparency" of the core, the stair shaft remains the symbol of movement between the essentially independent floors via the "neutral" stair shaft. The solution is economic because it permits an optimum relationship between access space and usable floor space and, through repetition of identical building elements, enables a rational construction process. Above a certain height of building this makes stair cores indispensable.

Stair shafts, or rather their outer walls, which are often solid to comply with the thermal, acoustic and fire requirements, can be used to brace the building, as the plan of the Pirelli Headquarters shows. The system of walls separating stair shafts and ancillary rooms brace the building in the longitudinal direction. As main access is via the lifts in the middle of the building, the stair shafts occupy only a minimum area and are located in poché-type spaces at the ends of the curved blocks.

By way of contrast to the above emergency stairs we should consider the stair shaft of the Palazzo Barberini. This stair shaft is an impressive combination of the goals of a spectacle and a rational, vertical connection. The size of the stairwell creates an effective three-dimensional space extending over six storeys.

The three-dimensional interior layout attempts to minimise the contrast between vertical and horizontal

Fig. 12: Gio Ponti: Pirelli Headquarters, Milan (I), 1961
Fig. 13: Francesco Borromini: Palazzo Barberini, Rome (I), 1633

movement by merging horizontal and vertical circulation areas within a three-dimensional continuum. The spatial barriers between the storeys can be broken down further by introducing split levels, inclined planes and ramps. This permits almost unlimited manipulation of the hierarchy among the storeys. A promenade architecturale is created: the topmost storey becomes the end of a promenade, a lift becomes a time machine.

The spatial plans of Adolf Loos were one attempt to overcome the conventional breakdown into storeys, to achieve a three-dimensional interior layout. It became possible to give different spaces different ceiling heights according to their usage. The offsets between the individual levels resulted in plenty of freedom in the design of living quarters. Numerous short stairs formed a route through the interior, leading gradually to more private areas.

Some of the designs from O.M.A. are related to these spatial concepts although they stem from a completely different Zeitgeist. Contemporary technology enables us to deform the floor slabs at will, to overcome the classical subdivision of horizontal and vertical, and to allow the ground floor to flow upwards as a continuous band without a real staircase.

Thoroughfare and stopping-place

Stairs that are reduced to their practical function form vertical bridges between different levels and are designed purely as thoroughfares. We stop perhaps only briefly to exchange words with another staircase-user, or for a rest.

Otherwise, such staircases are purely circulation areas and lead from one place to another. Depending on the ratio of the anticipated foot traffic and the dimensions of the stair, stopping for a moment can hinder the flow of people, even endanger their safety. In fact, specific measures can cultivate or influence the nature of the flow of people on a stair. Countless stairs in underground stations throughout the world demonstrate how a flowing movement of the mass can be promoted with an additional dynamic parallel with or in the direction of the flow.

Fig. 15: O.M.A.: Jussieu University library project, Paris (F), 1993
Fig. 16: Paris Metro, stairs

What turns a staircase into a stopping-place or a place for communication? In terms of their actual width and steepness, the stairs leading to the entrances of the Bouça publicly assisted housing development are no different to the thoroughfare stairs described above. However, people are happy to sit here, to while away the hours with chitchat. Critical aspects are the proportions of the flights and the relationship between the foot traffic expected and the width of the stair. Whether a stair acts as a catalyst for communication of course depends on the utilisation at both ends of the stair and how it relates to its immediate environment. The lighting, the microclimate and, possibly, the view can represent animating factors. Who doesn't prefer a wide open view to a confined perspective?

However, the stair also offers the advantage of being able to see beyond the person in front, a fact which has been exploited for thousands of years in the arrangement of audiences. These places normally serve one-way communication; those on the grandstand are the consumers. The steeper the terracing, the better our view and the greater the feeling of being exposed to what is being offered; it is harder to hide behind the person in front. However, if we place two grandstands opposite each other, multiple communication is possible. The discussion forums of history made use of this arrangement, a fact that is copied by contemporary televised discussions. One variation on this type of collective communication is the singing by blocks of fans in sports stadiums; this is only possible thanks to the stepped, grandstand form.

Further reading

- Karl J. Habermann: Staircases - Design and Construction, Basel, Boston, Berlin, 2003.

- John Templer: The staircase Voi.1+2, Cambridge, Mass., 1992

- Cleo Baldon: Steps & stairways, New York, 1989.

- Walter M. Förderer: "Treppenräume", in: Daidaios, No. 9, 1983

- Wolfgang Meisenheimer: "Treppen als Bühnen der Raum-Anschauung", ir Daidaios, No. 9, 1983.

- Ulrich Giersch: "Auf Stufen", in: Daidaios, No. 9, 1983

Further reading

- Karl J. Habermann: Staircases - Design and Construction, Basel, Boston, Berlin, 2003.

- John Templer: The staircase Voi.1+2, Cambridge, Mass., 1992

- Cleo Baldon: Steps & stairways, New York, 1989.

- Walter M. Förderer: "Treppenräume", in: Daidaios, No. 9, 1983

- Wolfgang Meisenheimer: "Treppen als Bühnen der Raum-Anschauung", ir Daidaios, No. 9, 1983.

- Ulrich Giersch: "Auf Stufen", in: Daidaios, No. 9, 1983

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