A roof ( : roofs or rooves) is the top covering of a

building A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and funct ...

, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against

rain Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water ...

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

, sunlight, extremes of

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

, and

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...

. A roof is part of the

building envelope A building envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noiseSyed, Asif. ''Advanced building technologies for sustainability''. Hoboke ...

. The characteristics of a roof are dependent upon the purpose of the building that it covers, the available roofing materials and the local traditions of

construction Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and ...

and wider concepts of architectural design and practice, and may also be governed by local or national

legislation Legislation is the process or result of enrolling, enacting, or promulgating laws by a legislature, parliament, or analogous governing body. Before an item of legislation becomes law it may be known as a bill, and may be broadly referred to ...

. In most countries, a roof protects primarily against rain. A

verandah A veranda or verandah is a roofed, open-air gallery or porch, attached to the outside of a building. A veranda is often partly enclosed by a railing and frequently extends across the front and sides of the structure. Although the form ''vera ...

may be roofed with material that protects against sunlight but admits the other elements. The roof of a garden conservatory protects plants from cold, wind, and rain, but admits light. A roof may also provide additional living space, for example, a roof garden.

Etymology

Old English 'roof, ceiling, top, summit; heaven, sky', also figuratively, 'highest point of something', from

Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic bran ...

( cf. Dutch 'deckhouse, cabin, coffin-lid',

Middle High German Middle High German (MHG; german: Mittelhochdeutsch (Mhd.)) is the term for the form of German spoken in the High Middle Ages. It is conventionally dated between 1050 and 1350, developing from Old High German and into Early New High German. High ...

'penthouse', Old Norse 'boat shed'). There are no apparent connections outside the Germanic family. "English alone has retained the word in a general sense, for which the other languages use forms corresponding to OE. thatch".

Design elements

The elements in the design of a roof are: * the material * the

* the durability The material of a roof may range from

banana A banana is an elongated, edible fruit – botanically a berry (botany), berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa (genus), Musa''. In some countries, Cooking banana, bananas used for ...

leaves, wheaten

straw Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has a numbe ...

seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...

to laminated glass,

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...

''(see: copper roofing)'',

aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...

sheeting and pre-cast concrete. In many parts of the world

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...

roof tiles have been the predominant roofing material for centuries, if not millennia. Other roofing materials include

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...

, coal tar pitch, EPDM rubber, Hypalon, polyurethane foam, PVC,

slate Slate is a fine-grained, foliated, 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 ro ...

, Teflon fabric, TPO, and wood shakes and shingles. The construction of a roof is determined by its method of support and how the underneath space is bridged and whether or not the roof is ''pitched''. The '' pitch'' is the angle at which the roof rises from its lowest to highest point. Most US domestic architecture, except in very dry regions, has roofs that are sloped, or ''pitched''. Although modern construction elements such as drainpipes may remove the need for pitch, roofs are pitched for reasons of tradition and aesthetics. So the pitch is partly dependent upon stylistic factors, and partially to do with practicalities. Some types of roofing, for example

thatch Thatching is the craft of building a roof with dry vegetation such as straw, water reed, sedge (''Cladium mariscus''), rushes, heather, or palm branches, layering the vegetation so as to shed water away from the inner roof. Since the bulk of ...

, require a steep pitch in order to be waterproof and durable. Other types of roofing, for example pantiles, are unstable on a steeply pitched roof but provide excellent weather protection at a relatively low angle. In regions where there is little rain, an almost flat roof with a slight run-off provides adequate protection against an occasional downpour. Drainpipes also remove the need for a sloping roof. A person that specializes in roof construction is called a roofer. The durability of a roof is a matter of concern because the roof is often the least accessible part of a building for purposes of repair and renewal, while its damage or destruction can have serious effects.

Form

The shape of roofs differs greatly from region to region. The main factors which influence the shape of roofs are the climate and the materials available for roof structure and the outer covering. The basic shapes of roofs are flat, mono-pitched,

gable A gable is the generally triangular portion of a wall between the edges of intersecting roof pitches. The shape of the gable and how it is detailed depends on the structural system used, which reflects climate, material availability, and aest ...

mansard A mansard or mansard roof (also called a French roof or curb roof) is a four-sided gambrel-style hip roof characterised by two slopes on each of its sides, with the lower slope, punctured by dormer windows, at a steeper angle than the upper. The ...

hipped In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region ...

butterfly Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprises ...

arch An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vau ...

ed and

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a ...

d. There are many variations on these types. Roofs constructed of flat sections that are sloped are referred to as pitched roofs (generally if the angle exceeds 10 degrees). Pitched roofs, including gabled, hipped and skillion roofs, make up the greatest number of domestic roofs. Some roofs follow organic shapes, either by architectural design or because a flexible material such as thatch has been used in the construction.

Parts

There are two parts to a roof: its supporting structure and its outer skin, or uppermost weatherproof layer. In a minority of buildings, the outer layer is also a self-supporting structure. The roof structure is generally supported upon walls, although some building styles, for example,

geodesic In geometry, a geodesic () is a curve representing in some sense the shortest path ( arc) between two points in a surface, or more generally in a Riemannian manifold. The term also has meaning in any differentiable manifold with a connection. ...

and A-frame, blur the distinction between wall and roof.

Support

The supporting structure of a roof usually comprises beams that are long and of strong, fairly rigid material such as

timber Lumber is wood that has been processed into dimensional lumber, including Beam (structure), beams and plank (wood), planks or boards, a stage in the process of wood production. Lumber is mainly used for construction framing, as well as fini ...

, and since the mid-19th century,

cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impu ...

or steel. In countries that use

bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...

extensively, the flexibility of the material causes a distinctive curving line to the roof, characteristic of Oriental architecture. Timber lends itself to a great variety of roof shapes. The timber structure can fulfil an aesthetic as well as practical function, when left exposed to view. Stone lintels have been used to support roofs since prehistoric times, but cannot bridge large distances. The stone arch came into extensive use in the

ancient Roman In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 B ...

period and in variant forms could be used to span spaces up to across. The stone arch or vault, with or without ribs, dominated the roof structures of major architectural works for about 2,000 years, only giving way to iron beams with the

Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...

and the designing of such buildings as Paxton's Crystal Palace, completed 1851. With continual improvements in steel girders, these became the major structural support for large roofs, and eventually for ordinary houses as well. Another form of

girder A girder () is a support beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders often have an I-beam cross section composed of two load-bearing ''flanges'' separated by a stabilizing ...

is the reinforced concrete beam, in which metal rods are encased in concrete, giving it greater strength under tension. Roof support can also serve as living spaces as can be seen i
roof decking
Roof decking are spaces within the roof structure that is converted into a room of some sort.

Outer layer

This part of the roof shows great variation dependent upon availability of material. In

vernacular architecture Vernacular architecture is building done outside any academic tradition, and without professional guidance. This category encompasses a wide range and variety of building types, with differing methods of construction, from around the world, bo ...

, roofing material is often vegetation, such as thatches, the most durable being

sea grass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...

with a life of perhaps 40 years. In many Asian countries bamboo is used both for the supporting structure and the outer layer where split bamboo stems are laid turned alternately and overlapped. In areas with an abundance of timber, wooden shingles, shakes and

boards Board or Boards may refer to: Flat surface * Lumber, or other rigid material, milled or sawn flat ** Plank (wood) ** Cutting board ** Sounding board, of a musical instrument * Cardboard (paper product) * Paperboard * Fiberboard ** Hardboard, ...

are used, while in some countries the

bark Bark may refer to: * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, ...

of certain trees can be peeled off in thick, heavy sheets and used for roofing. The 20th century saw the manufacture of composition asphalt shingles which can last from a thin 20-year shingle to the thickest which are limited lifetime shingles, the cost depending on the thickness and durability of the shingle. When a layer of shingles wears out, they are usually stripped, along with the underlay and roofing nails, allowing a new layer to be installed. An alternative method is to install another layer directly over the worn layer. While this method is faster, it does not allow the roof sheathing to be inspected and water damage, often associated with worn shingles, to be repaired. Having multiple layers of old shingles under a new layer causes roofing nails to be located further from the sheathing, weakening their hold. The greatest concern with this method is that the weight of the extra material could exceed the dead load capacity of the roof structure and cause collapse. Because of this, jurisdictions which use the

International Building Code The International Building Code (IBC) is a model building code developed by the International Code Council (ICC). It has been adopted for use as a base code standard by most jurisdictions in the United States. The IBC addresses both health and sa ...

prohibit the installation of new roofing on top of an existing roof that has two or more applications of any type of roof covering; the existing roofing material must be removed before installing a new roof.

Slate Slate is a fine-grained, foliated, 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 ro ...

is an ideal, and durable material, while in the

Swiss Alps The Alpine region of Switzerland, conventionally referred to as the Swiss Alps (german: Schweizer Alpen, french: Alpes suisses, it, Alpi svizzere, rm, Alps svizras), represents a major natural feature of the country and is, along with the Sw ...

roofs are made from huge slabs of stone, several inches thick. The slate roof is often considered the best type of roofing. A slate roof may last 75 to 150 years, and even longer. However, slate roofs are often expensive to install – in the US, for example, a slate roof may have the same cost as the rest of the house. Often, the first part of a slate roof to fail is the fixing nails; they corrode, allowing the slates to slip. In the UK, this condition is known as "nail sickness". Because of this problem, fixing nails made of stainless steel or

are recommended, and even these must be protected from the weather. Asbestos, usually in bonded corrugated panels, has been used widely in the 20th century as an inexpensive, non-flammable roofing material with excellent insulating properties.

Health Health, according to the World Health Organization, is "a state of complete physical, mental and social well-being and not merely the absence of disease and infirmity".World Health Organization. (2006)''Constitution of the World Health Organiza ...

and legal issues involved in the mining and handling of asbestos products means that it is no longer used as a new roofing material. However, many asbestos roofs continue to exist, particularly in South America and Asia. Roofs made of cut turf (modern ones known as

green roof A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainag ...

s, traditional ones as sod roofs) have good insulating properties and are increasingly encouraged as a way of "greening" the Earth. The soil and vegetation function as living insulation, moderating building temperatures. Adobe roofs are roofs of clay, mixed with binding material such as straw or animal hair, and plastered on lathes to form a flat or gently sloped roof, usually in areas of low rainfall. In areas where clay is plentiful, roofs of baked tiles have been the major form of roofing. The casting and firing of roof tiles is an industry that is often associated with brickworks. While the shape and colour of tiles was once regionally distinctive, now tiles of many shapes and colours are produced commercially, to suit the taste and pocketbook of the purchaser. Concrete roof tiles are also a common choice, being available in many different styles and shapes.

Sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes. Thicknesses can vary significantly; ex ...

in the form of

and

lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

has also been used for many hundreds of years. Both are expensive but durable, the vast copper roof of

Chartres Cathedral Chartres Cathedral, also known as the Cathedral of Our Lady of Chartres (french: Cathédrale Notre-Dame de Chartres), is a Roman Catholic church in Chartres, France, about southwest of Paris, and is the seat of the Bishop of Chartres. Mostly ...

, oxidised to a pale green colour, having been in place for hundreds of years. Lead, which is sometimes used for church roofs, was most commonly used as flashing in valleys and around chimneys on domestic roofs, particularly those of slate. Copper was used for the same purpose. In the 19th century, iron, electroplated with

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic t ...

to improve its resistance to rust, became a light-weight, easily transported, waterproofing material. Its low cost and easy application made it the most accessible commercial roofing, worldwide. Since then, many types of metal roofing have been developed. Steel shingle or standing-seam roofs last about 50 years or more depending on both the method of installation and the moisture barrier (underlayment) used and are between the cost of shingle roofs and slate roofs. In the 20th century, a large number of roofing materials were developed, including roofs based on bitumen (already used in previous centuries), on rubber and on a range of synthetics such as

thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associat ...

and on

fibreglass Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass clot ...

. File:The Elms Jersey.jpg, Slate,

Jersey Jersey ( , ; nrf, Jèrri, label=Jèrriais ), officially the Bailiwick of Jersey (french: Bailliage de Jersey, links=no; Jèrriais: ), is an island country and self-governing Crown Dependencies, Crown Dependency near the coast of north-west F ...

File:Miskolc omassa peasant house.jpg, Terracotta tiles,

Hungary Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croa ...

File:Niigata NCM Peasant Rice Farmers House.jpg, Thatch, using rice straw, Japan File:Njem house in Cameroon.jpg, Banana leaves,

Cameroon Cameroon (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west- central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; th ...

File:Neot smadar.jpg,

Date palm ''Phoenix dactylifera'', commonly known as date or date palm, is a flowering plant species in the palm family, Arecaceae, cultivated for its edible sweet fruit called dates. The species is widely cultivated across northern Africa, the Middle Ea ...

branches,

Neot Semadar Neot Smadar ( he, נְאוֹת סְמָדַר, lit. ''Oasis of blossoming vines'') is a kibbutz in southern Israel. Located in the Arava Desert, it falls under the jurisdiction of Hevel Eilot Regional Council. Its area is 80 hectares. In it had ...

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

File:Minenverwalter Kolmannskuppe.jpg, Metal sheeting,

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and e ...

File:Gassho-zukuri farmhouse-02.jpg, Repairing thatch, Gassho-zukuri farmhouse, Japan File:Stone Roofing House - Palchan - Kullu 2014-05-10 2507.JPG, Stone used as roofing material in

Himachal Pradesh Himachal Pradesh (; ; "Snow-laden Mountain Province") is a state in the northern part of India. Situated in the Western Himalayas, it is one of the thirteen mountain states and is characterized by an extreme landscape featuring several peak ...

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

File:Green Roof in Norway.png, Turf roof in

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

Functions

A roof assembly has more than one function. It may provide any or all of the following functions:
1. To shed water i.e., prevent water from standing on the roof surface. Water standing on the roof surface increases the live load on the roof structure, which is a safety issue. Standing water also contributes to premature deterioration of most roofing materials. Some roofing manufacturers' warranties are rendered void due to standing water.
2. To protect the building interior from the effects of weather elements such as rain, wind, sun, heat and snow.
3. To provide thermal insulation. Most modern commercial/industrial roof assemblies incorporate insulation boards or batt insulation. In most cases, the International Building Code and International Residential Code establish the minimum R-value required within the roof assembly.
4. To perform for the expected service life. All standard roofing materials have established histories of their respective longevity, based on anecdotal evidence. Most roof materials will last long after the manufacturer's warranty has expired, given adequate ongoing maintenance, and absent storm damage. Metal and tile roofs may last fifty years or more. Asphalt shingles may last 30–50 years. Coal tar built-up roofs may last forty or more years. Single-ply roofs may last twenty or more years.
5. Provide a desired, unblemished appearance. Some roofs are selected not only for the above functions, but also for aesthetics, similar to wall cladding. Premium prices are often paid for certain systems because of their attractive appearance and "curb appeal."

Insulation

Because the purpose of a roof is to secure people and their possessions from climatic elements, the insulating properties of a roof are a consideration in its structure and the choice of roofing material. Some roofing materials, particularly those of natural fibrous material, such as thatch, have excellent insulating properties. For those that do not, extra insulation is often installed under the outer layer. In developed countries, the majority of dwellings have a ceiling installed under the structural members of the roof. The purpose of a ceiling is to insulate against heat and cold, noise, dirt and often from the droppings and lice of birds who frequently choose roofs as nesting places. Concrete tiles can be used as insulation. When installed leaving a space between the tiles and the roof surface, it can reduce heating caused by the sun. Forms of insulation are felt or plastic sheeting, sometimes with a reflective surface, installed directly below the tiles or other material; synthetic foam batting laid above the ceiling and recycled paper products and other such materials that can be inserted or sprayed into roof cavities. Cool roofs are becoming increasingly popular, and in some cases are mandated by local codes. Cool roofs are defined as roofs with both high

reflectivity The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electroni ...

and high thermal emittance. Poorly insulated and ventilated roofing can suffer from problems such as the formation of ice dams around the overhanging eaves in cold weather, causing water from melted snow on upper parts of the roof to penetrate the roofing material. Ice dams occur when heat escapes through the uppermost part of the roof, and the snow at those points melts, refreezing as it drips along the shingles, and collecting in the form of ice at the lower points. This can result in structural damage from stress, including the destruction of gutter and drainage systems.

Drainage

The primary job of most roofs is to keep out water. The large area of a roof repels a lot of water, which must be directed in some suitable way, so that it does not cause damage or inconvenience. Flat roof of adobe dwellings generally have a very slight slope. In a Middle Eastern country, where the roof may be used for recreation, it is often walled, and drainage holes must be provided to stop water from pooling and seeping through the porous roofing material. Similar problems, although on a very much larger scale, confront the builders of modern commercial properties which often have flat roofs. Because of the very large nature of such roofs, it is essential that the outer skin be of a highly impermeable material. Most industrial and commercial structures have conventional roofs of low pitch. In general, the pitch of the roof is proportional to the amount of precipitation. Houses in areas of low rainfall frequently have roofs of low pitch while those in areas of high rainfall and snow, have steep roofs. The

longhouse A longhouse or long house is a type of long, proportionately narrow, single-room building for communal dwelling. It has been built in various parts of the world including Asia, Europe, and North America. Many were built from timber and often rep ...

s of

Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

, for example, being roof-dominated architecture, the high roofs sweeping almost to the ground. The high steeply-pitched roofs of Germany and Holland are typical in regions of snowfall. In parts of North America such as

Buffalo, New York Buffalo is the second-largest city in the U.S. state of New York (behind only New York City) and the seat of Erie County. It is at the eastern end of Lake Erie, at the head of the Niagara River, and is across the Canadian border from Sou ...

, United States, or

Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...

, Quebec, Canada, there is a required minimum slope of 6 in 12 (1:2, a pitch of 30°). There are regional building styles which contradict this trend, the stone roofs of the Alpine chalets being usually of gentler incline. These buildings tend to accumulate a large amount of snow on them, which is seen as a factor in their insulation. The pitch of the roof is in part determined by the roofing material available, a pitch of 3 in 12 (1:4) or greater slope generally being covered with asphalt shingles, wood shake, corrugated steel, slate or tile. The water repelled by the roof during a rainstorm is potentially damaging to the building that the roof protects. If it runs down the walls, it may seep into the mortar or through panels. If it lies around the foundations it may cause seepage to the interior, rising damp or

dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resu ...

. For this reason most buildings have a system in place to protect the walls of a building from most of the roof water. Overhanging

eaves The eaves are the edges of the roof which overhang the face of a wall and, normally, project beyond the side of a building. The eaves form an overhang to throw water clear of the walls and may be highly decorated as part of an architectural sty ...

are commonly employed for this purpose. Most modern roofs and many old ones have systems of valleys, gutters, waterspouts, waterheads and drainpipes to remove the water from the vicinity of the building. In many parts of the world, roofwater is collected and stored for domestic use. Areas prone to heavy snow benefit from a metal roof because their smooth surfaces shed the weight of snow more easily and resist the force of wind better than a wood shingle or a concrete tile roof. File:Snow on the roof.jpg,

Snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

on the roofs of houses in

Poland Poland, officially the Republic of Poland, , is a country in Central Europe. Poland is divided into Voivodeships of Poland, sixteen voivodeships and is the fifth most populous member state of the European Union (EU), with over 38 mill ...

File:Ashdod 2005, rooftop view p2.JPG, The flat roofs of the Middle East,

File:Jakriborg, juni 2005 x.jpg, Steeply pitched, gabled roofs in Northern Europe File:雪中紫禁城 7.jpg, The overhanging eaves of China File:PA120016.JPG,

Green roof A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainag ...

with solar panels, Findhorn,

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...

Solar roofs

Newer systems include solar shingles which generate

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...

as well as cover the roof. There are also solar systems available that generate hot water or hot air and which can also act as a roof covering. More complex systems may carry out all of these functions: generate electricity, recover thermal energy, and also act as a roof covering. Solar systems can be integrated with roofs by: : integration in the covering of pitched roofs, e.g. solar shingles, : mounting on an existing roof, e.g.

solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a pho ...

on a

tile Tiles are usually thin, square or rectangular coverings manufactured from hard-wearing material such as ceramic, Rock (geology), stone, metal, baked clay, or even glass. They are generally fixed in place in an array to cover roofs, floors, wa ...

roof, : integration in a flat roof membrane using heat welding (e.g. PVC) or : mounting on a flat roof with a construction and additional weight to prevent uplift from wind.

Gallery of roof shapes

File:Five roofs of Toji-ji, Kyoto.jpg, Five roofs of Toji-ji,

Kyoto Kyoto (; Japanese: , ''Kyōto'' ), officially , is the capital city of Kyoto Prefecture in Japan. Located in the Kansai region on the island of Honshu, Kyoto forms a part of the Keihanshin metropolitan area along with Osaka and Kobe. , the ...

File:Thai-roof.jpg, Pitched roof with decorated gable, Chang Mai,

Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...

File:Valsta säteri.jpg, Sateri roof (with vertical break in pitch), Sweden File:mount-gilead-ohio-jail.jpg, Mansard roof, county jail, Mount Gilead, Ohio File:National_Taiwan_Science_Education_Center_Chinese_Roof.jpg, Conical roof, Nanhai Academy in

Taipei Taipei (), officially Taipei City, is the capital and a special municipality of the Republic of China (Taiwan). Located in Northern Taiwan, Taipei City is an enclave of the municipality of New Taipei City that sits about southwest of the ...

File:Concrete roof insulation in Haikou, Hainan, China - 04.JPG, Flat roofs,

Haikou Haikou (; ), also spelled as Hoikow is the capital and most populous city of the Chinese province of Hainan. Haikou city is situated on the northern coast of Hainan, by the mouth of the Nandu River. The northern part of the city is on the ...

City, Hainan, China File:Mandurah house.jpg, Sloped flat roof, house,

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to ...

File:William Krisel butterfly roof home in Paradise Palms.jpg,

Butterfly roof A butterfly roof (sometimes called a V roof) is a form of roof characterised by an inversion of a standard roof form, with two roof surfaces sloping down from opposing edges to a valley near the middle of the roof. File:Hospices de beaune toit.jpg, The polychrome tiles of the Hospices de Beaune,

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...

. File:SydneyOperaHouse6 gobeirne.jpg, The glazed ceramic tiles of the

Sydney Opera House The Sydney Opera House is a multi-venue performing arts centre in Sydney. Located on the foreshore of Sydney Harbour, it is widely regarded as one of the world's most famous and distinctive buildings and a masterpiece of 20th-century archit ...

. File:Coupole du mihrab, Grande Mosquée de Kairouan.jpg, Ashlar masonry dome of the Great Mosque of Kairoun, Tunisia File:Cupola santamariadelfiore.jpg, Imbrex and tegula tiles on the dome of Florence Cathedral. File:Taj gumbad.jpg, The marble dome of the

Taj Mahal The Taj Mahal (; ) is an Islamic ivory-white marble mausoleum on the right bank of the river Yamuna in the Indian city of Agra. It was commissioned in 1631 by the Mughal emperor Shah Jahan () to house the tomb of his favourite wife, Mu ...

. File:Speyerer Dom Dach.jpg, The copper roof of

Speyer Cathedral , native_name_lang = German , image = Speyer_dom_11.jpg , imagesize = 280px , imagelink = , imagealt = , landscape = , caption = , pushpin ma ...

, Germany. File:Kings chapel roof.jpg, The lead roof of King's College Chapel,

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. File:Grand Palaais 501590 fh000033.jpg, The glass roof of the

Grand Palais The Grand Palais des Champs-Élysées ( en, Great Palace of the Elysian Fields), commonly known as the Grand Palais ( English: Great Palace), is a historic site, exhibition hall and museum complex located at the Champs-Élysées in the 8th ...

Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. ...

References

{{Authority control Structural engineering Structural system