Copper in architecture
Copper has earned a respected place in the related fields of architecture, building construction, interior design. From cathedrals to castles and from homes to offices, copper is used for a variety of architectural elements, including roofs, gutters, domes, vaults, wall cladding, building expansion joints; the history of copper in architecture can be linked to its durability, corrosion resistance, prestigious appearance, ability to form complex shapes. For centuries and designers utilized these attributes to build aesthetically pleasing and long-lasting building systems. For the past quarter century, copper has been designed into a much wider range of buildings, incorporating new styles, varieties of colors, different shapes and textures. Copper clad walls are a modern design element in both outdoor environments; some of the world's most distinguished modern architects have relied on copper. Examples include Frank Lloyd Wright. Architect Frank O. Gehry’s enormous copper fish sculpture atop the Vila Olimpica in Barcelona is an example of the artistic use of copper.
Copper's most famous trait is its display from a bright metallic colour to iridescent brown to near black and to a greenish verdigris patina. Architects describe the array of browns as russet, plum and ebony; the metal's distinctive green patina has long been coveted by designers. This article describes practical and aesthetic benefits of copper in architecture as well as its use in exterior applications, interior design elements, green buildings. Copper has played a role in architecture for thousands of years. For example, in ancient Egypt, massive doors to the temple of Amen-Re at Karnak were clad with copper. In the 3rd Century B. C. copper roof shingles were installed atop of the Lowa Maha Paya Temple in Sri Lanka. And the Romans used copper as roof covering for the Pantheon in 27 B. C. Centuries copper and its alloys were integral in medieval architecture; the doors of the Church of the Nativity at Bethlehem are covered with plates of bronze, cut out in patterns. Those of Hagia Sophia at Constantinople, of the 8th and 9th century, are wrought in bronze.
Bronze doors on the Aachen Cathedral in Germany date back to about 800 A. D. Bronze baptistery doors at the Cathedral of Florence were completed in 1423 A. D. by Ghiberti. The copper roof of Hildesheim Cathedral, installed in 1280 A. D. survives to this day. And the roof at Kronborg, one of northern Europe's most important Renaissance castles, immortalized as Elsinore Castle in Shakespeare's Hamlet, was installed in 1585 A. D; the copper on the tower was renovated in 2009. For years, copper was reserved for public institutions, such as churches, government buildings, universities. Copper roofs are one of the most architecturally distinguishable features of these structures. Today, architectural copper is used in roofing systems and copings, rain gutters and downspouts, building expansion joints, wall cladding, spires and various other design elements; the metal has evolved from a weather barrier and exterior design element into indoor building environments where it is changing the way commercial and residential interiors are decorated.
In the 21st century, the use of copper continues to evolve in the indoor environment. Its proven antimicrobial properties reduce pathogenic bacterial loads on such products as handrails, bathroom fixtures, counter tops, etc; these antimicrobial copper-based products are now being incorporated into public facilities as well as in residential buildings because of the public health benefits. As an architectural metal, copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coatings that protect underlying copper surfaces and resist corrosion for a long time. Copper corrodes at negligible rates in unpolluted air, water, de-aerated non-oxidizing acids, when exposed to saline solutions, alkaline solutions, organic chemicals. Copper roofing in rural atmospheres corrodes at rates of less than 0.4 mm in 200 years. Unlike most other metals, copper does not suffer from underside corrosion that can cause premature failures in roofing. With a copper roof, supporting substrates and structures fail long before the copper on the roof.
Architectural copper is, susceptible to corrosive attack under certain conditions. Oxidizing acids, oxidizing heavy-metal salts, alkalis and nitrogen oxides and some sulfur and ammonium compounds can expedite copper corrosion. Precipitation in areas with a pH less than 5.5 may corrode copper before a patina or protective oxide film has the time to form. Acidic precipitation, known as acid rain, is due to emissions from fossil fuel combustion, chemical manufacturing, or other processes that release sulfur and nitrogen oxides into the atmosphere. Erosion corrosion may occur when acidic water from a non-copper roof that does not neutralise the acidity, such as tile, wood, or asphalt, falls on a small area of copper. Line corrosion can occur if the d
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Slate is a fine-grained, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression; the foliation in slate is called "slaty cleavage". It is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression; when expertly "cut" by striking parallel to the foliation, with a specialized tool in the quarry, many slates will display a property called fissility, forming smooth flat sheets of stone which have long been used for roofing, floor tiles, other purposes. Slate is grey in color when seen, en masse, covering roofs. However, slate occurs in a variety of colors from a single locality. Slate is not to schist; the word "slate" is used for certain types of object made from slate rock.
It may mean a writing slate. They were traditionally a small, smooth piece of the rock framed in wood, used with chalk as a notepad or noticeboard, for recording charges in pubs and inns; the phrases "clean slate" and "blank slate" come from this usage. Before the mid-19th century, the terms slate and schist were not distinguished. In the context of underground coal mining in the United States, the term slate was used to refer to shale well into the 20th century. For example, roof slate referred to shale above a coal seam, draw slate referred to shale that fell from the mine roof as the coal was removed. Slate is composed of the minerals quartz and muscovite or illite along with biotite, chlorite and pyrite and, less apatite, kaolinite, tourmaline, or zircon as well as feldspar; as in the purple slates of North Wales, ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen.
Slate can be made into roofing slates, a type of roof shingle, or more a type of roof tile, which are installed by a slater. Slate has two lines of breakability – cleavage and grain – which make it possible to split the stone into thin sheets; when broken, slate retains a natural appearance while remaining flat and easy to stack. A "slate boom" occurred in Europe from the 1870s until the first world war, allowed by the use of the steam engine in manufacturing slate tiles and improvements in road and waterway transportation systems. Slate is suitable as a roofing material as it has an low water absorption index of less than 0.4%, making the material waterproof. In fact, this natural slate, which requires only minimal processing, has the lowest embodied energy of all roofing materials. Natural slate is used by building professionals as a result of its durability. Slate is durable and can last several hundred years with little or no maintenance, its low water absorption makes it resistant to frost damage and breakage due to freezing.
Natural slate is fire resistant and energy efficient. Slate roof tiles are fixed either with nails, or with hooks as is common with Spanish slate. In the UK, fixing is with double nails onto timber battens or nailed directly onto timber sarking boards. Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives. Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 80–100 years; some mainland European slate suppliers suggest that using hook fixing means that: Areas of weakness on the tile are fewer since no holes have to be drilled Roofing features such as valleys and domes are easier to create since narrow tiles can be used Hook fixing is suitable in regions subject to severe weather conditions, since there is greater resistance to wind uplift, as the lower edge of the slate is secured. The metal hooks are, however and may be unsuitable for historic properties. Slate tiles are used for interior and exterior flooring, stairs and wall cladding.
Tiles are grouted along the edges. Chemical sealants are used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, increase or reduce surface smoothness. Tiles are sold gauged, meaning that the back surface is ground for ease of installation. Slate flooring can be slippery. Slate tiles were used in 19th century UK building construction and in slate quarrying areas such as Blaenau Ffestiniog and Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can be set into walls to provide a rudimentary damp-proof membrane. Small offcuts are used as shims to level floor joists. In areas where slate is plentiful it is used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone. In modern homes slate is used as table coasters; because it is a good electrical insulator and fireproof, it was used to construct early-20th-century electric switchboards and relay controls for large electric motors.
Fine slate can be used as a whe
Madagascar the Republic of Madagascar, known as the Malagasy Republic, is an island country in the Indian Ocean 400 kilometres off the coast of East Africa. The nation comprises the island of Madagascar and numerous smaller peripheral islands. Following the prehistoric breakup of the supercontinent Gondwana, Madagascar split from the Indian subcontinent around 88 million years ago, allowing native plants and animals to evolve in relative isolation. Madagascar is a biodiversity hotspot; the island's diverse ecosystems and unique wildlife are threatened by the encroachment of the growing human population and other environmental threats. The first archaeological evidence for human foraging on Madagascar may have occurred as much as 10,000 years ago. Human settlement of Madagascar occurred between 350 BC and 550 AD by Austronesian peoples, arriving on outrigger canoes from Borneo; these were joined around the 9th century AD by Bantu migrants crossing the Mozambique Channel from East Africa. Other groups continued to settle on Madagascar over time, each one making lasting contributions to Malagasy cultural life.
The Malagasy ethnic group is divided into 18 or more subgroups, of which the largest are the Merina of the central highlands. Until the late 18th century, the island of Madagascar was ruled by a fragmented assortment of shifting sociopolitical alliances. Beginning in the early 19th century, most of the island was united and ruled as the Kingdom of Madagascar by a series of Merina nobles; the monarchy ended in 1897 when the island was absorbed into the French colonial empire, from which the island gained independence in 1960. The autonomous state of Madagascar has since undergone four major constitutional periods, termed republics. Since 1992, the nation has been governed as a constitutional democracy from its capital at Antananarivo. However, in a popular uprising in 2009, president Marc Ravalomanana was made to resign and presidential power was transferred in March 2009 to Andry Rajoelina. Constitutional governance was restored in January 2014, when Hery Rajaonarimampianina was named president following a 2013 election deemed fair and transparent by the international community.
Madagascar is a member of the United Nations, the African Union, the Southern African Development Community, the Organisation Internationale de la Francophonie. Madagascar belongs according to the United Nations. Malagasy and French are both official languages of the state; the majority of the population adheres to traditional beliefs, Christianity, or an amalgamation of both. Ecotourism and agriculture, paired with greater investments in education and private enterprise, are key elements of Madagascar's development strategy. Under Ravalomanana, these investments produced substantial economic growth, but the benefits were not evenly spread throughout the population, producing tensions over the increasing cost of living and declining living standards among the poor and some segments of the middle class; as of 2017, the economy has been weakened by the 2009–2013 political crisis, quality of life remains low for the majority of the Malagasy population. In the Malagasy language, the island of Madagascar is called Madagasikara and its people are referred to as Malagasy.
The island's appellation "Madagascar" is not of local origin but rather was popularized in the Middle Ages by Europeans. The name Madageiscar was first recorded in the memoirs of 13th-century Venetian explorer Marco Polo as a corrupted transliteration of the name Mogadishu, the Somali port with which Polo had confused the island. On St. Laurence's Day in 1500, Portuguese explorer Diogo Dias landed on the island and named it São Lourenço. Polo's name popularized on Renaissance maps. No single Malagasy-language name predating Madagasikara appears to have been used by the local population to refer to the island, although some communities had their own name for part or all of the land they inhabited. At 592,800 square kilometres, Madagascar is the world's 47th largest country and the fourth-largest island; the country lies between latitudes 12°S and 26°S, longitudes 43°E and 51°E. Neighboring islands include the French territory of Réunion and the country of Mauritius to the east, as well as the state of Comoros and the French territory of Mayotte to the north west.
The nearest mainland state is Mozambique, located to the west. The prehistoric breakup of the supercontinent Gondwana separated the Madagascar–Antarctica–India landmass from the Africa–South America landmass around 135 million years ago. Madagascar split from India about 88 million years ago during the late Cretaceous period allowing plants and animals on the island to evolve in relative isolation. Along the length of the eastern coast runs a narrow and steep escarpment containing much of the island's remaining tropical lowland forest. To the west of this ridge lies a plateau in the center of the island ranging in altitude from 750 to 1,500 m above sea level; these central highlands, traditionally the homeland of the Merina people and the location of their historic capital at Antananarivo, are the most densely populated part of the island and are characterized by terraced, rice-growing valleys lying between grassy hills and patches of the subhumid forests that covered the highland region. To the west of the highlands, the arid terrain slope
Domestic roof construction
Domestic roof construction is the framing and roof covering, found on most detached houses in cold and temperate climates. Such roofs are built with timber, take a number of different shapes, are covered with a variety of materials. Modern timber roofs are framed with pairs of common rafters or prefabricated wooden trusses fastened together with truss connector plates. Timber framed and historic buildings may be framed with principal rafters or timber roof trusses. Roofs are designated as warm or cold roof depending on how they are designed and built with regard to thermal building insulation and ventilation; the steepness or roof pitch of a sloped roof is determined by the roof covering material and aesthetic design. Flat roofs slope up to ten degrees to shed water. Flat roofs on houses are found in arid regions. In high wind areas, such as where a cyclone or hurricane may make landfall, the main engineering consideration is to hold the roof down during severe storms; every component of the roof, as of course the rest of the structure, has to withstand the uplift forces of high wind speeds.
This is accomplished by using metal ties fastened to truss. This is not a problem in areas not prone to high wind or extreme weather conditions. In the UK, a concrete tiled roof would have rafters at 600mm centers, roof battens at 300mm centers and ceiling joists at 400mm centers; the United States still uses imperial units of measurement and framing members are spaced sixteen or twenty-four inches apart. The roof framing may be interrupted for openings such as skylight. Chimneys are built with a water diverter known as a cricket or saddle above the chimney. Flashing is used to seal the gap between the roofing material. A simple rafter roof consists of rafters that the rafter foot rest on horizontal wall plates on top of each wall; the top ends of the rafters meet at a ridge beam, but may butt directly to another rafter to form a pair of rafters called a couple. Depending on the roof covering material, either horizontal laths, battens, or purlins are fixed to the rafters. Heavier under purlins or purlin plates are used to support longer rafter spans.
Tie beams, which may serve as ceiling joists, are connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength; the rafters, tie beams and plates serve to transmit the weight of the roof to the walls of the building Pre-manufactured roof trusses come in a wide variety of styles. They are designed by the manufacturer for each specific building. Timber trusses are built in a variety of styles using wood or metal joints. Heavy timber rafters spaced 8 feet to 12 feet apart are called principal rafters. Principal rafters may carry common purlins. Roof framing must be designed to hold up a structural load including what is called dead load, its own weight and the weight of the roof covering, additional loading called the environmental load such as snow and wind. Flat roofs may need to be designed for live loads if people can walk on them. In the United States, building codes specify the loads in pounds per square foot which vary by region.
The load and span defines the spacing of the rafters and trusses. The roofing material is designed to shed water; the covering is a major element of the architecture so roofing materials come in a wide variety of colors and textures. The primary roof covering on houses in North America are asphalt shingles, but some have other types of roof shingles or metal roofs. Tile and thatch roofs are more common in Europe than North America; some roofing materials help reduce air conditioning costs in hot climates by being designed to reflect light. Asphalt shingles is the most used roofing material in North America, making up as much as 75% of all steep slope roofs; this type of material is gaining popularity in Europe due to lower installation costs. Asphalt shingles dominate North American residential roofing market, because they are about half the price of other materials In the southern US and Mexico, clay tile roofs are very popular, due to their longevity, ability to withstand hurricane winds with minimal or no damage.
In Europe and tile roofs are popular. Many slate roofs in Europe are over 100 years old, require minimal maintenance / repairs. Roof space ventilation is needed to combat condensation within the roof space, leading to interstitial condensation within the roof fabric. Condensation within the roof space is much more of a problem today due to: much less fortuitous ventilation due to tighter building envelopes with high performance windows and door and no chimneys leading; this tighter envelope means the air temperature in buildings has risen, the warmer the air in the building is, the more water vapour the air can carry. As the occupied part of building has become warner, the roof space has become colder, with high performance insulation and roofing membranes leading to a cold roof space; when the warm, moist air from below rises into the cold roof space. Most building materials are permeable to water vapour.
Wood shingles are thin, tapered pieces of wood used to cover roofs and walls of buildings to protect them from the weather. Shingles were split from straight grained, knot free bolts of wood. Today shingles are made by being cut which distinguishes them from shakes which are made by being split out of a bolt. Wooden shingle roofs were prevalent in the North American colonies, while in central and southern Europe at the same time, thatch and tile were the prevalent roofing materials. In rural Scandinavia, wood shingle roofs were a common roofing material until the 1950s. Wood shingles are susceptible to fire and cost more than other types of shingle so they are not as common today as in the past. Distinctive shingle patterns exist in various regions created by the size and application method. Special treatments such as swept valleys, combed ridges, decorative butt ends, decorative patterns impart a special character to each building. Wood shingles can be shaped by steam bending to create a thatch-like appearance, with unique roof details and contours.
Wooden shingles were thin narrow, of varying length, always planed or knifed smooth. The traditional method for making wooden shingles before the 19th century was to rive them from straight-grained knot-free sections of logs pre-cut to the desired length known as bolts; these bolts were split into wedges. A mallet and froe were used to rive out thin pieces of wood; the wood species varied according to available local woods, but only the more durable heartwood, or inner section, of the log was used. The softer sapwood was not used because it deteriorated quickly; because hand-split shingles were somewhat irregular along the split surface, it was necessary to dress or plane the shingles on a shaving horse with a drawknife or draw-shave to make them fit evenly on the roof. This reworking was necessary to provide a tight-fitting roof over open shingle lath or sheathing boards. Dressing, or smoothing of shingles, was universal, no matter what wood was used or in what part of the world the building was located, except in those cases where a temporary or utilitarian roof was needed.
Shingle fabrication was revolutionized in the early 19th century by steam-powered saw mills. Shingle mills made possible the production of uniform shingles in mass quantities; the sawn shingle of uniform taper and smooth surface eliminated the need to hand dress. The supply of wooden shingles was therefore no longer limited by local factors; these changes coincided with the popularity of architectural styles such as Carpenter Gothic, Queen Anne, Shingle style architecture that used shingles to great effect. Hand-split shingles continued to be used in many places well after the introduction of machine sawn shingles. There were, of course, other popular roofing materials, some regions rich in slate had fewer examples of wooden shingle roofs; some western "boom" towns used sheet metal because it was light and shipped. Slate and clay tile were used on ornate buildings and in cities that limited the use of flammable wooden shingles. Wooden shingles, were never abandoned. In the 20th century, architectural styles such as the Colonial Revival and Tudor Revival used wooden shingles.
The simplest form of wood shingle is a rectangle about 16 inches long. The sides and butt of a shingle are irregular. Shingles that have been processed so that the butt is square to the sides are called rebutted and re-squared or rebutted and re-jointed shingles abbreviated R&R. Shingles and shakes may be tapered, split or sawn and any combination of these except straight-tapered. Different species and quality of wood are used. Shakes and shingles may be treated with wood preservatives and fire retardants before or after installation. A shake is a basic wooden shingle made from split logs. Shakes have traditionally been used for siding applications around the world. Higher-grade shakes are used for roofing purposes, while the lower grades are used for siding. In either situation, properly installed shakes provide long-lasting weather protection and a rustic aesthetic, though they require more maintenance than some other more modern weatherproofing systems; the term shake is sometimes used as a colloquialism for all wood shingles, though shingles are sawn rather than split.
In traditional usage, "shake" refers to the board. Split wooden shingles are referred to as shag shingles. Modern wooden shingles, both sawn and split, continue to be made, but they differ from the historic ones. Modern commercially available shakes are thicker than the historic handsplit counterpart and are left "undressed" with a rough, corrugated surface; the rough-surface shake is considered to be more "rustic" and "historic", but in fact this is a modern fashion. Some modern shingles are produced in pre-cut decorative patterns, sometimes called fancy-cut shingles, are available pre-primed for painting; the sides of rectangular shingles may be re-squared and re-butted, which means they have been reworked so the sides are parallel and the butt is square to the sides. These are installed more neatly as a result. Shingles are less durable than shakes in wet climates.
A flat roof is a roof, level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to 10°. Flat roofs are an ancient form used in arid climates and allow the roof space to be used as a living space or a living roof. Flat roofs, or "low-slope" roofs, are commonly found on commercial buildings throughout the world; the National Roofing Contractors Association defines a low-slope roof as having a slope of 3-in-12 or less. Flat roofs exist all over the world and each area has its own tradition or preference for materials used. In warmer climates, where there is less rainfall and freezing is unlikely to occur, many flat roofs are built of masonry or concrete and this is good at keeping out the heat of the sun and cheap and easy to build where timber is not available. In areas where the roof could become saturated by rain and leak, or where water soaked into the brickwork could freeze to ice and thus lead to'blowing' these roofs are not suitable.
Flat roofs are characteristic of the Egyptian and Arabian styles of architecture. Any sheet of material used to cover a flat or low-pitched roof is known as a membrane and the primary purpose of these membranes is to waterproof the roof area. Materials that cover flat roofs allow the water to run off from a slight inclination or camber into a gutter system. Water from some flat roofs such as on garden sheds sometimes flows off the edge of a roof, though gutter systems are of advantage in keeping both walls and foundations dry. Gutters on smaller roofs lead water directly onto the ground, or better, into a specially made soakaway. Gutters on larger roofs lead water into the rainwater drainage system of any built up area. However, flat roofs are designed to collect water in a pool for aesthetic purposes, or for rainwater buffering. Traditionally most flat roofs in the western world make use of tar or asphalt more felt paper applied over roof decking to keep a building watertight; the felt paper is in turn covered with a flood coat of bitumen and gravel to keep the sun's heat, UV rays and weather off it and helps protect it from cracking or blistering and degradation.
Roof decking is of plywood, chipboard or OSB boards of around 18mm thickness, steel or concrete. The mopping of bitumen is applied in two or more coats as a hot liquid, heated in a kettle. A flooded coat of bitumen is applied over the felts and gravel is embedded in the hot bitumen. A main reason for failure of these traditional roofs is ignorance or lack of maintenance where people or events cause the gravel to be moved or removed from the roof membrane called a built-up roof, thus exposing it to weather and sun. Cracking and blistering occurs and water gets in. Roofing felts are a'paper' or fiber material impregnated in bitumen; as gravel cannot protect tarpaper surfaces where they rise vertically from the roof such as on parapet walls or upstands, the felts are coated with bitumen and protected by sheet metal flashings. In some microclimates or shaded areas these rather'basic' felt roofs can last well in relation to the cost of materials purchase and cost of laying them, however the cost of modern membranes such as EPDM has come down over recent years to make them more and more affordable.
There are now firms supplying modern alternatives. If a leak does occur on a flat roof, damage goes unnoticed for considerable time as water penetrates and soaks the decking and any insulation and/or structure beneath; this can lead to expensive damage from the rot which develops and if left can weaken the roof structure. There are health risks to people and animals breathing the mould spores: the severity of this health risk remains a debated point. While the insulation is wet, the “R” value is destroyed. If dealing with an organic insulation, the most common solution is removing and replacing the damaged area. If the problem is detected early enough, the insulation may be saved by repairing the leak, but if it has progressed to creating a sunken area, it may be too late. One problem with maintaining flat roofs is that if water does penetrate the barrier covering, it can travel a long way before causing visible damage or leaking into a building where it can be seen. Thus, it is not easy to find the source of the leak.
Once underlying roof decking is soaked, it sags, creating more room for water to accumulate and further worsening the problem. Another common reason for failure of flat roofs is lack of drain maintenance where gravel and debris block water outlets; this causes a pressure head of water which can crack. In colder climates, puddling water can freeze, it is therefore important to maintain your flat roof to avoid excessive repair. An important consideration in tarred flat roof quality is knowing that the common term'tar' applies to rather different products: tar or pitch, coal tar and bitumen; some of these products appear to have been interchanged in their use and are sometimes used inappropriately, as each has different characteristics, for example whether or not the product can soak into wood, its anti-fungal properties and its reaction to exposure to sun and varying temperatures. Modern flat roofs can use single large