Roofer

Roofers working on a bungalow in Brompton, Quebec
Occupation
Occupation type	Vocational
Activity sectors	Construction
Description
Competencies	Heights, patience, steady hand, ability to read plans, physically strong
Education required	Apprenticeship
Fields of employment	Construction
Related jobs	Carpenter, Electrician, Plumber, Welder

A roofer, roof mechanic, or roofing contractor is a tradesman who specializes in roof construction. Roofers replace, repair, and install the roofs of buildings, using a variety of materials, including shingles, single-ply, bitumen, and metal. Roofing work includes the hoisting, storage, application, and removal of roofing materials and equipment, including related insulation, sheet metal, vapor barrier work, and green technologies rooftop jobs such as vegetative roofs, rainwater harvesting systems, and photovoltaic products, such as solar shingles and solar tiles.^[1][2]

Roofing work can be physically demanding because it may involve heavy lifting, climbing, bending, and kneeling, often in extreme weather conditions.^[1] Roofers are also vulnerable to falls from heights due to working at elevated heights. Various protective measures are required in many countries. In the United States these requirement are established by the Occupational Safety and Health Administration (OSHA) to address this concern.^[3][4][5] Several resources from occupational health agencies are available on implementing the required and other recommended interventions.^[6][7][8]

According to data from the U.S. Bureau of Labor Statistics (BLS), as of May 2022^[update], there were 129,300 individuals working as roofers in the construction industry. Among that population, a majority of roofers (93%; 119,800) were contractors for Foundation, Structure, and Building Exterior projects.^[9][10] In terms of jobs outlook, it is predicted that there will only be a 2% increase in job growth from 2022 to 2032 in the United States. Approximately 12,200 openings are expected each year in this decade. Most of the new jobs are likely to be offered to replace roofers who retire or transition out of the trade.^[1]

In Australia, this type of carpenter is called a roof carpenter and the term roofer refers to someone who installs the roof cladding (tiles, tin, etc.). The number of roofers in Australia was estimated to be approximately 15,000. New South Wales is the largest province with an 29% market share in the Australian Roofers industry (4,425 companies). Second is Victoria with 3,206 Roofers (21%).^[11]

In the United States and Canada, they're often referred to as roofing contractors or roofing professionals. The most common roofing material in the United States is asphalt shingles. In the past, 3-tab shingles were used, but recent trends show "architectural" or "dimensional" shingles becoming very popular.^[12]

Depending on the region, other commonly applied roofing materials installed by roofers include concrete tiles, clay tiles, natural or synthetic slate, single-ply (primarily EPDM rubber, PVC, or TPO), rubber shingles (made from recycled tires), glass, metal panels or shingles, wood shakes or shingles, liquid-applied, hot asphalt/rubber, foam, thatch, and solar tiles. "Living roof" systems, or rooftop landscapes, have become increasingly common in recent years in both residential and commercial applications.^[13][14]

Roles and responsibilities of roofing professionals include:^[1]

• Assessing the roof system and components (may include decking and structural components)
• Determining the proper roofing system for the building
• Installing roof system components according to manufacturer’s specifications
• Repairing the roof system
• Maintenance of the roof system

Beyond having common duties such as replacing, repairing, or installing roofs for buildings, roofers can also be involved in other tasks, including but is not limited to:

• Seal exposed heads of nails or screws using roofing cement or caulk to avert possible water infiltration
• Tailor roofing materials to accommodate architectural elements such as walls or vents
• Align the installed materials with the roof's edges to ensure a proper fit
• Apply various roofing materials such as shingles, asphalt, metal, etc., to render the roof impervious to weather conditions
• Establish roof ventilation mechanisms to regulate airflow and control temperature fluctuations
• Set up moisture barriers or insulation layers to improve the roof's thermal performance
• Dismantle the current roof systems to make ways for repairs or new installations
• Substitute impaired or decaying joists or plywood to maintain the roof's structural integrity
• Assess roof dimensions to assess the necessary amount of required materials
• Conduct evaluations on problematic roofs to determine the most effective repair approach

Roofing is one of the most dangerous professions among construction occupations since it involves working at heights and exposes workers to dangerous weather conditions such as extreme heat.^[15] In the United States as of 2017, the rate of fatalities from falls among roofers is 36 deaths per 100,000 full-time employees, ten times greater than all construction-related professions combined.^[16] In the United States, the fatal injury rate in 2021 was 59.0 per 100,000 full-time roofers, compared to the national average of 3.6 per 100,000 full-time employees.^[17] According to the U.S. Bureau of Labor Statistics, roofing has been within the top 5 highest death rates of any profession for over 10 years in a row.^[18] For Hispanic roofers, data from 2001–2008 show fatal injuries from falls account for nearly 80% of deaths in this population, the highest cause of death among Hispanics of any construction trade.^[19][20]

A major contributing factor to the high fatality rates among roofers in the United States is the nature of the craft which requires roofers to work on elevated, slanted roof surfaces. Findings from qualitative interviews with Michigan roofing contractors also found hand and finger injuries from handling heavy material and back injuries to be some of the more common task/injury combinations.^[21]

Ladder falls contribute to the rates of injury and mortality. More than half a million people per year are treated for fall from ladder and over 3000 people die as a result.^[22] In 2014 the estimated cost annual cost of ladder injuries, including time away from work, medical, legal, liability expenses was estimated to reach $24 billion.^[22] Male, Hispanic, older, self-employed workers and those who work in smaller establishments, and work doing construction, maintenance, and repair experience higher ladder fall injury rates when compared with women and non-Hispanic whites and persons of other races/ethnicities.^[23]

Ladders allow for roofers to access upper level work surfaces. For safe use, ladder must be inspected for damage by a competent person and must be used on stable and level surfaces unless they are secured to prevent displacement.^[3]

Nearly every industrialized country has established specific safety regulations for work on the roof, ranging from the use of conventional fall protection systems including personal fall arrest systems, guardrail systems, and safety nets.

The European Agency for Safety and Health at Work describes scenarios of risk (fall prevention, falling materials, types of roofs), precautions, training needed and European legislation focused on roof work.^[6] European directives set minimum standards for health and safety and are transposed into law in all Member States.

In the United States, OSHA standards require employers to have several means of fall protection available to ensure the safety of workers. In construction, this applies to workers who are exposed to falls of 6 feet or more above lower levels.^[3][24] In the United States, regulation of the roofing trade is left up to individual states. Some states leave roofing regulation up to city-level, county-level, and municipal-level jurisdictions. Unlicensed contracting of projects worth over a set threshold may result in stiff fines or even time in prison. In some states, roofers are required to meet insurance and roofing license guidelines. Roofers are also required to display their license number on their marketing material.

Canada's rules are very similar to those from the U.S., and regulatory authority depends on where the business is located and fall under the authority of their local province.

In 2009, in response to high rates of falls in constructions the Japanese Occupational Safety and Health Regulations and Guidelines amended their specific regulations. In 2013 compliance was low and the need for further research and countermeasures for preventing falls and ensuring fall protection from heights was identified.^[25]

The United Kingdom has no legislation in place that requires a roofer to have a license to trade, although some do belong to recognized trade organizations.^[26]

The purpose of a PFAS is to halt a fall and prevent the worker from making bodily contact with a surface below. The PFAS consists of an anchorage, connectors, body harness and may include a lanyard, deceleration device, lifeline or suitable combination of these.

Beyond these mandatory components of the PFAS, there are also specific fall distances associated with the functioning of the arrest system. Specifically, there is a total fall distance that the PFAS must allow for to assist the worker in avoiding contact with the ground or other surface below. The total fall distance consists of free fall distance, deceleration distance, D-ring shift, Back D-ring height, and Safety margin. In addition to the fall distance requirements for each component of the PFAS, the anchorage of the PFAS must also be able to support a minimum 5,000 pounds per worker.^[4]

OSHA regulations have several requirements. The free fall distance, to the distance that the worker drops before the PFAS begins to work and slows the speed of the fall, must be 6 feet or less, nor contact any lower level. The deceleration, the length that the lanyard must stretch in order to arrest the fall must be no more than 3.5 feet.^[4] The D-ring shift, the distance that the harness stretches and how far the D-ring itself moves when it encounters the full weight of the worker during a fall, is generally assumed to be 1 foot, depending on the equipment design and the manufacturer of the harness. For the back D-ring height, the distance between the D-ring and the sole of the worker's footwear, employers often use 5 feet as the standard height with the assumption that the worker will be 6 feet in height, but because the D-ring height variability can affect the safety of the system, the back D-ring height must be calculated based on the actual height of the worker. The safety margin, the additional distance that is needed to ensure sufficient clearance between the worker and the surface beneath the worker after a fall occurs, is generally considered to be a minimum of 2 feet.^[3]

A fall restraint system is a type of fall protection system where, the goal is to stop workers from reaching the unprotected sides or edges of a working area in which a fall can subsequently occur. This system is useful where a worker may lose their footing near an unprotected edge or begin sliding. In such a case, the fall restraint system will restrain further movement of the worker toward the unprotected side or edge and prevent a serious fall. Although fall restraint systems are not explicitly defined or mentioned in OSHA's fall protection standards for construction,^[24][4] they are allowed by OSHA as specified in an OSHA letter of interpretation last updated in 2004.^[27] OSHA does not have any specific requirements for fall restraint systems, but recommends that any fall restraint system be capable of withstanding 3,000 pounds or at least twice the maximum predicted force necessary to save the worker from falling to the lower surface.^[3] There are no OSHA specifications on the distance from the edge the restraint system must allow for a falling worker, and although a likely very dangerous practice, the OSHA letter of interpretation states that as long as the restraint system prevents the employee from falling off an edge, the employee can be restrained to "within inches of the edge."^[27]

Guardrail systems serve as an alternative to PFAS and fall restraint systems by having permanent or temporary guardrails around the perimeter of the roof and any roof openings. OSHA requires the height of the top of the rail to be 39-45 inches above the working surface. Mid-rails must be installed midway between the top of the top rail and the walking/working surface when there is no parapet wall at least 21 inches high. Guardrail systems must be capable of withstanding 200-pounds of force in any outward or downward direction applied within 2 inches of the top edge of the rail.^[3][24]

Safety net systems use a tested safety net adjacent to and below the edge of the walking/working surface to catch a worker who may fall off the roof. Safety nets must be installed as close as practicable under the surface where the work is being performed and shall extend outward from the outermost projection of the work surface as follows:^[4]

^[4]

Safety nets must be drop-tested with a 400-pound bag of sand, or submit a certification record prior to its initial use.^[4]

Warning lines systems consist of ropes, wires, or chains which are marked every 6 feet with high-visibility material, and must be supported in such a way so that it is between 34 and 39 inches above the walking/working surface.^[4] Warning lines are passive systems that allow for a perimeter to be formed around the working area so that workers are aware of dangerous edges. Warning lines are only permitted on roofs with a low slope (having a slope of less than or equal to 4 inches of vertical rise for every 12 inches horizontal length (4:12)).^[28] In the context of roofing fall protection, warning line systems may only be used in combination with a guardrail system, a safety net system, a personal fall arrest system, or a safety monitoring system. The warning line system must be erected around all sides of the roof work area.^[4]

Safety monitoring systems use safety monitors to monitor the safety of other workers on the roof. Safety monitors must be competent to recognize fall hazards. The safety monitor is tasked to ensure the safety of other workers on the roof and must be able to orally warn an employee when they are in an unsafe situation.^[4]

Multi-layered approaches to fall prevention and protection that use the hierarchy of controls can help to prevent fall injuries, incidents, and fatalities in the roofing industry.^[7][8] The hierarchy of controls is a way of determining which actions will best control exposures. The hierarchy of controls has five levels of actions to reduce or remove hazards – elimination, substitution, and engineering controls are among the preferred preventive actions based on general effectiveness.

Resources are available to assist with the implementation of fall safety measures in the roofing industry such as fall prevention plans,^[23][29] a ladder safety mobile application,^[30] infographics and tipsheets,^[31] toolbox talks,^[32] videos and webinars,[1] and safety leadership training.[2] Many of these resources are available in Spanish and additional languages other than English. The recommended safety measures are described next.

In terms of job outlooks, it is predicted that there will only be an 1% increase in job growth from 2021 to 2032. The job openings (15,000) are expected to replace roofers who will retire or transition out of the trade.^[9]

Solar Roof installation is one of the fastest growing trends in the roofing industry due to the nature of solar roofs being environmentally friendly and a worthwhile economic investment. Specifically, solar roofs have been found to allow homeowners to potentially save 40-70% on electric bills depending on the number of tiles installed.^[33] The US federal government has also begun incentivizing homeowners to install solar roofs with potential eligibility for 30% tax credit on the cost of a solar system based on federal income taxes.^[34]

Across 14 researched markets, roofing contracting companies have reported that they have received more frequent calls regarding potential metal roof installations. For instance, one company used to receive 5-6 calls in total regarding metal installations but recently, they have received 5-6 calls weekly for inquiries regarding metal roof installations.^[35]

• Domestic roof construction
• Roof cleaning
• Flat roof
• Membrane roofing
• List of commercially available roofing materials
• Prevention through design

• Stop Construction Falls training and other resources from the Center for Construction Research and Training
  • Construction Toolbox Talks
  • Resources in Spanish and Additional Languages
• Construction Fatality Assessment and Control Evaluation (FACE) database, from the National Institute for Occupational Safety and Health and the Center for Construction Research and Training.
• Introduction to working at height safely from the Health Safety Executive, UK.
• Video NAPO: Working at height.
• Health and safety in roof work, from the Health Safety Executive, UK.
• Ladder safety resources from the National Institute for Occupational Safety and Health.
• You can prevent falls! from the Public Health Agency of Canada.
• Prevent Construction Falls from Roofs, Ladders, and Scaffolds, from the National Institute for Occupational Safety and Health.
• Roofing guidelines and recommendations, National Roofing Contractors Association.
• Education and Training Course Catalog, National Roofing Contractors Association.
• Occupational Employment and Wage Statistics, US Bureau of Labor Statistics.
• Infographics and Tipsheets. The Center for Construction Research and Training.

Wikimedia Commons has media related to Roofers.

Top covering of a building

"Rooftop" redirects here. For other uses, see Rooftop (disambiguation) and Roof (disambiguation).

 

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A roof (pl.: roofs or rooves) is the top covering of a building, including all materials and constructions necessary to support it on the walls of the building or on uprights, providing protection against rain, snow, sunlight, extremes of temperature, and wind.^[1] A roof is part of the building envelope.

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 and wider concepts of architectural design and practice, and may also be governed by local or national legislation. In most countries, a roof protects primarily against rain. A verandah 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

[edit]

Old English hrof^[2] 'roof, ceiling, top, summit; heaven, sky', also figuratively, 'highest point of something', from Proto-Germanic *khrofam (cf. Dutch roef 'deckhouse, cabin, coffin-lid', Middle High German rof 'penthouse', Old Norse hrof '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. þæc thatch".^[3]

Design elements

[edit]

The elements in the design of a roof are:

• the material
• the construction
• the durability

The material of a roof may range from banana leaves, wheaten straw or seagrass to laminated glass, copper (see: copper roofing), aluminium sheeting and pre-cast concrete. In many parts of the world ceramic roof tiles have been the predominant roofing material for centuries, if not millennia. Other roofing materials include asphalt, coal tar pitch, EPDM rubber, Hypalon, polyurethane foam, PVC, slate, 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 its 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, 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

[edit]

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.^[4]

The basic shapes of roofs are flat, mono-pitched, gabled, mansard, hipped, butterfly, arched and domed. 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).^[5] 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.

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

The supporting structure of a roof usually comprises beams that are long and of strong, fairly rigid material such as timber, and since the mid-19th century, cast iron or steel. In countries that use bamboo 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 period and in variant forms could be used to span spaces up to 45 m (140 ft) 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 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 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 in roof decking. Roof decking are spaces within the roof structure that is converted into a room of some sort.

This part of the roof shows great variation dependent upon availability of material. In vernacular architecture, roofing material is often vegetation, such as thatches, the most durable being sea grass 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 are used, while in some countries the bark 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 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.^[6]

Slate is an ideal, and durable material, while in the Swiss Alps 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 copper are recommended, and even these must be protected from the weather.^[7]

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 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 roofs, 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.^[8] 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 in the form of copper and lead has also been used for many hundreds of years. Both are expensive but durable, the vast copper roof of Chartres Cathedral, 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 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 and on fibreglass.

• Outer layer
• 
  Slate, Jersey
• 
  Terracotta tiles, Hungary
• 
  Thatch, using rice straw, Japan
• 
  Banana leaves, Cameroon
• 
  Date palm branches, Neot Semadar, Israel
• 
  Metal sheeting, Namibia
• 
  Repairing thatch, Gassho-zukuri farmhouse, Japan
• 
  Stone used as roofing material in Himachal Pradesh, India
• 
  Turf roof in Norway

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."

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,^[9] and in some cases are mandated by local codes. Cool roofs are defined as roofs with both high reflectivity and high thermal emittance.^[9]

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.

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.

While flat roofs are more prone to drainage issues, poorly designed or textured sloping roofs can face similar problems.^[10] Standing water on a roof can lead to mold growth, which is highly damaging to both the building’s structure and the health of its occupants. Repairing drainage issues is significantly less costly than fixing the damage caused by mold.^[11]

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 longhouses of Papua New Guinea, 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, United States, or Montreal, 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. 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 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.

• Insulation, drainage and solar roofing
• 
  Snow on the roofs of houses in Poland
• 
  The flat roofs of the Middle East, Israel
• 
  Steeply pitched, gabled roofs in Northern Europe
• 
  The overhanging eaves of China
• 
  Green roof with solar panels, Findhorn, Scotland

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Newer systems include solar shingles which generate electricity 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 on a tile 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.

• Roof shapes
• 
  Five roofs of Toji-ji, Kyoto
• 
  Pitched roof with decorated gable, Chiang Mai, Thailand
• 
  Säteri roof (with vertical break in pitch), Sweden
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  Mansard roof, county jail, Mount Gilead, Ohio
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  Conical roof, Nanhai Academy in Taipei
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  Flat roofs, Haikou City, Hainan, China
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  Sloped flat roof, house, Western Australia
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  Butterfly roof in Paradise Palms in the southwestern United States

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  The polychrome tiles of the Hospices de Beaune, France.
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  The glazed ceramic tiles of the Sydney Opera House.
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  Ashlar masonry dome of the Great Mosque of Kairoun, Tunisia
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  Imbrex and tegula tiles on the dome of Florence Cathedral.
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  The marble dome of the Taj Mahal.
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  The copper roof of Speyer Cathedral, Germany.
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  The lead roof of King's College Chapel, England.
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  The glass roof of the Grand Palais, Paris.
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  A slate roof in Syrrako (Greece), built with a curved valley layout and finials on top.

• Blue roof
• Building-integrated photovoltaics
• Domestic roof construction
• List of Greco-Roman roofs
• List of roof shapes
• Roof cleaning
• Rubber shingle roof
• Solar shingle
• Tensile architecture
• Thin-shell structure

Wikimedia Commons has media related to Roofs.