METALS and ROOFS ● Part – I

Post 379 – by Gautam Shah 

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Miller_Park_in_2007

Roofs of buildings have been formed of smaller components such as ceramic tiles, slate stones, stone slabs, and grasses (thatched) or of masonry domes. Leakage of water and air were chief problems. These were solved by provision of acute slopes for drainage, design of joints, and use of joints’ sealants. Other problems included structural integrity against vibrations (earthquake and usage), accommodation of stresses (thermal, wind and loadings) and maintenance through repairs and replacement.

Home_in_rural_Bangladesh

 

Metals are the lightest and thin body materials for roofing. Lead and copper, have been most widely exploited-metals, till coated steel products became available. Metals are used for roofing elements such as for main body cover, flashing or joint making, and drainage system including, gutters, spout and pipes. A metal roofing system can have all components made from different metals. Such multi metal systems are used for mechanical advantages of installation but not for galvanic protection. Performance, maintenance, service life, and recovery costs determine the cost effectiveness of metal roofing components.

Warsaw Palace Copper Roof with vertical seams

Copper has been a favoured roofing material for two main reasons: 1. It is fairly durable when it can form bluish-green patina and, 2. It can be bent, stretched or moulded into difficult -doubly curved shapes. Copper sheets used for roofing are easy to shape over curved structures such as cupolas and domes. Copper roofing sheets can be forged joined for greater lengths. Copper sheets or panels are lighter than wooden shingles, and much lighter than slate, ceramic tiles, or stone slabs.

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Copper roofs are prone to galvanic erosion, unless isolated from other conductive elements. Copper is a universal roofing material as it is used for cover, gutters, flashing, coping and spouts. Copper is an ideal for flashing as it is malleable and easily workability, solder-able with tin, and is resistant to Alkaline environments. It is easy to hammer or work into watertight joints, without any caulk or the gasket. Copper is reusable material.

Copper covered cupola St Maria Florence

Copper roofing system is essentially how joints are formed. One of the simplest ways is to create a lapped joint with a soldered rim. But such a joint of tin, may not architecturally match the green-blue patina. So, concealed seam joints filled with a tin solder lining are preferred. To accommodate the seam thickness, the joints are used for nailing to batten and the seam folded over to form horizontal steps or vertical line marks. For flatter or low-pitched roofs the seams are folded downward and the groove filled with a solder or caulking compound.

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A copper roof can stain adjacent building materials of lighter colours. Lead-coated copper can result in a black or gray stain. Proper design can avert such a situation. It may not be necessary to isolate copper from lead, tin or many stainless steels under most conditions. Some isolation can be achieved by using coatings including paints.

Vancouver Sun Tower Dome

Metal roofs do not add to risks of lightning strikes, as the metal disperses the electricity throughout the structure, lowering the damage by flash fire.

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ROOFS 3 -Skyline and Silhouette

Post 328 – by Gautam Shah

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All_Gizah_Pyramids

Roofs are most articulated elements of a building. Roofs form the skyline of a building, visible from a distance as a silhouette during twilight hours. A roof distinguishes a building among many other roofs. Roofs are single entity form covering nearly whole of structure, like for a pyramid or Pantheon. A roof could have a single domineering form, by height, mass or surface treatment. The roof mass is bloated by adding translucent forms like a belvedere, Chhatri, Turrets, galleries, Cupola, etc. These forms of varied sizes and shapes create an undulated edge over the roof.

The_Parthenon_in_Athens

Roofs have been important as they form a resonant skyline. Historical buildings formed a vibrant horizon by being on important terrain, large scale, height and the form. There are very few examples where a single roof structure (Parthenon) was created for dominance. Otherwise, several buildings forming a complex or an estate composed a variegated skyline. Such outlines were not pre-planned but evolved through deliberate additions and alterations over a period of time. In many cases the deliberations preceded with case study through on site sketches and scaled models.

Array_of_chhatris_over_the_entrance_of_Akbar's_Tomb,_Sikandra
The scenario has changed during the last century due to aircraft and satellites. Both have provided means of observing buildings from higher elevations. This has been a key factor in shape forming of not only high rise buildings but also large footprint structures. The composition of roofs (and entire structure) in making the skyline and silhouette, is pre-visualized for different atmospheric conditions, planned illuminations, and viewing positions including ground and air.

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These add-on architectural elements are rarely functional entities, or are connected with the main Interior spatial character of the building. There is an attempt to articulate their scale, sequencing, proportioning, scaling, etc. Well-designed buildings executed in one era usually have such well integrated roof elements. The integration is seen in ‘picturesque’ views from all sides and corners.

Westminster_palace

Roofs that are well integrated with the architectural layout of the building have a mutual affinity. One of the first such building is Hagia Sophia of Istanbul. It was the extra ordinary scale that perhaps did not allow any room for manipulation or decorative improvisations. Whatever one, perceives from outside, is the exact reflection of the interior space arrangement.

Istanbul_Hagia_Sophia_SultanahmedA similar roof related truthfulness is seen in many of the Gothic structures of an earlier era. In later periods the roofs have been loaded with many decorative elements, statuettes, etc. All Gothic roof structures rise up from their vertical elements, in one continuum.

Kodungallur-RD-11Nov11

Roofs, have been axially-balanced compositions, and also disarrayed mass arrangements. In case of religious buildings where the attention is focused, the building and its roof follow the same system. The composition could be single, multi-axial or cross axial, yet a balance roof emerges. This is also true of Government buildings, courts and other public buildings.

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Ahar_Cenotaphs

Roofs of single form covering the entire building have been used as the structure to seen and recognized from a distance or sky. Airports, Railway stations, Stadiums, etc. have single roof mounts. Space station workshops, aircraft hangers, large industrial plants have large functional space, enforcing single roof structures.

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Palaces and temples have very large vertical surface extent, and as a result the need for a bloated roof entity is not very strong. The roof lines are though undulated in various configurations. These structures have mixed roof structures, though well arranged but not in any formal or axial manner.

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OrchhaPalaceRoofs, in many buildings are, sloped structures. Sloped roof stretch the vertical face it abuts. This characteristic has been used in many buildings. Roofs have frontal slopes or side slopes accompanied by triangular pediment on main face.

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Modern buildings have roofs that acutely technical facilities. Few buildings have roof top public-use facilities like a view deck. But buildings’ skylines are designed to form a distinguishing entity in a mass of urban developments. Buildings are conceived to be visible and recognizable identity, in all types of weather and lighting conditions.

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ROOFS -2

Post 307- by Gautam Shah

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Yoyogi National stadium – Tensile structure by Kenzo Tange

Roofs as the outer most enclosure system of a building, define the form of an architectural entity. A heavy roof requires equally heavy sub structure, thus creating an effect of ‘solid or monumental building’, whereas a lighter roof system requires a lighter support structure, and seem very delicate or trivial. Roof-structures based on compressive elements are inherently heavier compared to tensile structures.

Circus tent

Roof systems are predominantly Compressive for several reasons. Roofs put up by comparatively non-mobile or stable societies are permanent, static, heavier in weight and well founded to grounds. These buildings have heavy bearing structure with fewer or smaller openings. Heavy roofs have low spanning capacity so interior spaces are small or narrow. The interiors are dark, compartmentalized and isolated from the outdoors. Heavy roof structures are hazardous for earth quake conditions. Construction of a heavy roof requires large manpower, through participation, coercion or money. Heavy roofs are ecologically inferior as there is inherent wastage of materials. Heavy roofs and their heavy support systems, require equally heavy foundation work which is difficult and a time-consuming proposition.

Dome structures Hauz Khas New Delhi India

 

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Roof systems are also tensile structures. These are light in weight, and so often demountable and portable. Such structures are preferred by nomadic or transient people. Light roof structures and their lighter support system, both offer free, open and bright interiors. Open interiors have an immediacy with the surroundings. Some structures are large span entities composed of very few elements, so are extremely adoptable to different internal arrangements. These structures unless well integrated with their support system and properly based to foundations are hazardous in wind storms. These structures with better cover material and appropriate pitch can be used in areas with heavy rainfall. These are ecologically very superior as there is inherent economy of materials and require very little foundation work. Execution is fast.

Thatched roof

Light weight roofing

Roofs have many different formsflat, pitched, vaulted, domed, etc., depending on the available materials and technology, architectural needs, and economic compulsions. Some of the primitive forms of roofs were, Pitched roofs with thatching, Conical roofs of hides, Flat roofs of stone slabs, and Gabled and flat roofs with rafters of dressed timbers. Plants, hides, and stone were the primary materials, gradually replaced with manufactured materials such as terracotta roofing tiles and woven mats. Coatings of primitive waterproofing compounds like tar, pitch, wax and fats continued for a very long period.

Richmond Olympic Oval composite wood beams

In low rain and hot-arid areas like Sind (Harappa) and Egypt flat roofs of heavy clay mass over wood structure were created to form terraces. Tropical countries with seasons of heavy rains had high pitched thatched roofs. Nomadic societies on Mongolia, Indians of Americas and Saharan regions developed demountable and transportable shelter system. These shelters had integrated roof and support system.

Bahai Lotus Temple Delhi India -folded plates

Roof systems occur as the outer most enclosure. An inclined roof has higher surface area, compared to a flat roof. An inclined roof has solar gain during part of the day when its inclined side faces the sun. This can be exploited for various locations. Roof forms are designed primarily to deal with the effects of environment. In high rain and snow fall areas roofs are designed for drainage. Roofs are also sloped to enlarge the roof surface area to receive higher solar insolation or sun light for energy conversion systems like heating pipes, solar power cells etc. Roof slopes are oriented to South or North faces, depending on the Northern or Southern hemisphere, respectively.

Abstract Mumbai Airport Ceiling

ROOFS and FLOORS (earlier article here)

 SLOPED ROOFS (earlier article here)

ROOFS and FLOORS

Post by Gautam Shah 

Thin shell roof

Roof and floor systems are called elements mediating across the load-bearing systems, such as walls and beams. Roofs by themselves may transmit the load, such as in Flat slabs, Shell structures, Domes, etc. Roofs can take various shapes, but Floors are flatter and only occasionally slightly inclined. The distinction of floor and beam or wall may or may not be very apparent. In some structures both are well integrated, so act coherently (e.g. waffle slabs). In other structures the identity of each is distinct yet they may operate interdependently. In assembled structures the components are independent, and easy to identify (a stone plate on a wall is simply supported). In cases where the structural support system and covering elements are integrated, the stress transfer is very efficient. This also results into a system that is lean and lightweight, when compared to system of independent (simply supported) components.

Frank Lloyd Wright Johnson Wax building Flat slab roof

Covering elements in Compressive roof systems are composed of stiff materials. These elements have a comparatively substantial thickness in proportion to the span. The thickness requirements vary depending on the composition of structure and the stress resistance of the material, the shape configuration of the covering element, the mode of stress transfer (across or along the section) and the end (support) conditions.

Brick vaulting

Covering elements in Tensile roofing systems are composed of stiff or flexible materials. The later have very small thickness in comparison to the size of the span. The material being very thin and flexible takes on the shape the way it is stressed to, and also depending on the gravity induced stress forms (catenary). Covering elements of a roofing system, when pre-stressed (usually pre-stretched), show greater resistance to various stresses.

Air inflated dome

For predominantly compressive elements, the shear capacity increases several fold. For tensile elements, the capacity to deal with local loads increases.

 

Covering material may be a homogeneous mass, a composition of smaller units or a layered mass. Covering materials in a roofing system are wood planks (shingles), plywood, laminated paper composites, fibre bitumen composites, fibre cement composites, ceramics, stones (slates, marbles, metamorphic rocks), glass, fibre-glass, cast in situ and pre-cast RCC, hollow blocks of cement and terracotta, cellular blocks, air entrained or expanded foam blocks, plastics, plastic foams, metal and alloy sheets, leaves, grass, sticks, natural fibres, mats, textiles, wool, synthetic woven materials, tarpaulins, impregnated fabrics, clay blocks, bricks, ice, ferro and magnesium cement castings, rubber sheets, nylon, Teflon, etc.

Crystal Palace -Glass roof-wall building

Louvre Paris Glass Pyramids as extension

A transparent roof cover material that would allow light and permit vision through was a dream, that every builder tried to realize. Romans used small glass disks inserts for roof illumination. Gothic period saw tall perpendicular windows almost merging into the roof. Paintings and murals with extensive skies as the theme were painted on the ceilings. However, it was the Conservatory at Derbyshire in 1836, Crystal Palace at London in 1850, both designed by Paxton, and the Palm house at Botanical Garden, Kew in 1845, designed by Burton and Turner, the dream of a transparent roof was realized. Transparent roofs are now made of acrylics and other plastics for solarium, green houses, passive solar heating systems, etc. Kenzo Tange designed the Japan Olympic stadium roof as a catenary – flexible structure. French museum Louvre at Paris has an extension wing with a glass pyramid.

A catenary roof structure Interior of Yoyogi Gymnasium Japan Olympic by Kenzo Tange

A catenary roof structure Exterior of Yoyogi Gymnasium Japan Olympic by Kenzo Tange

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Sloped Roofs

Post – by Gautam Shah

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Sloped Roofs are high or low pitched, single structures or assimilation of many sizes and pitches. Sloped roofs, make the skyline vibrant at any time of the day, and during evenings in illuminated city scapes. Sloped Roofs are heavy at the bottom, and so are gravity compliant. Sloped roofs seem stable even if project out of the nominal (structural) foot print of the buildings. In modern day scenario of Air Travel, sloped roofs make a fascinating urban scape.

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As a building element this are not tied by creation of functional spaces, placement of openings and literally sky is the limit to fly-out. The roofs are essentially external architectural statements and so variety of surface textures through materials and form-treatments are possible.

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Dresden Roofs > Wikipedia image by Heribert Pohl

Sloped roofs are of many different varieties. The simplest is the lean-to, or shed, which has slope in only one direction. A roof with two slopes that form an “A” or triangle is called a gable or pitched roof

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A hipped roof is a like gable roof but has slopes on all four sides.

640px-Osgood_Castle

Hipped Roofs > Osgood castle, Colorado USA > Wikipedia image by Jeffrey Beall

The gambrel roof is a type of gable roof with two pitches on two sides, the upper being less steep than the lower.

Mansard Roof

The mansard roof is a hipped gambrel roof, with double pitches on all sides.

Gambrel-Style_Barn

A pyramidal hipped roof, also known as a pavilion roof, is hipped equally at all corners and the hips meet at a single peak, but the common form of hip roof is above a rectangular structure, and so there would be a roof ridge meeting two hips at either end.

A variant is the half-hipped or jerkin head roof, which has gable ends truncated by the eaves of a small hip end (or jerkin head) that descends a short distance from the roof ridge. On an irregularly shaped structure, there may be more than four hips, which then may alternate with valleys, to form a hip-and-valley roof.

Folded Plate Roof

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