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					A roof is the covering on the uppermost part of a building. A roof protects the building and its
contents from the effects of weather. The characteristics of a roof are dependent upon the
purpose of the building that it covers, There is a wide spectrum of roof covering materials, which
are used for different structural, aesthetic, economic, and performance reasons. Roof designs
have developed from just being a weather performance element to an architectural trademark that
can be environment-friendly, structurally sound, reasonably priced and aesthetically attractive.




Parts of a roof
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 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 lamininated
glass, aluminium sheeting and precast concrete. In many parts of the world ceramic tiles have
been the predominant roofing material for centuries.
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 domestic architecture, except in very dry regions, has roofs
which are sloped, or pitched. example thatch, require a steep pitch in order to be waterproof and
durable.[1] 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.

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.

Types of Roofing

The most common types of roofing materials for residential structures are: asphalt shingles,
wood shingles and shakes, metal roofs, tile, slate and composite coverings.

Shingle - . A wide variety of shingles can be found with a variety of colors, styles, sizes and incorporating
unique performance and architectural features.

An asphalt shingle is a type of roof shingle. They are one of the most widely used
roofing covers because they are relatively inexpensive and fairly simple to install.

[edit]   Types of Asphalt Shingles
Two types of asphalt shingles are used: organic and fiberglass or glass fiber.
Organic shingles are generally paper (felt) saturated with asphalt to make it
waterproof, then a top coating of adhesive asphalt is applied and ceramic granules
are then embedded. In the case of algae-resistant shingles, a portion of the granules
contain leachable copper or tin designed to inhibit moss growth and discoloration
from algae on the roof.

Shingles are judged by weight per square. Organic shingles contain around 40%
more asphalt per square (100 sq. ft.) than fiberglass shingles which makes them
weigh more and gives them excellent durability and blow-off resistance. Shingle
durability is ranked by waranteed life, ranging from 20 years to 50 years; in some
cases lifetime warranties are available.

Fiberglass shingles have a base layer of glass fiber reinforcing mat. The glass fiber
mat is not waterproof by itself. Fiberglass mat is made from wet, random-laid
fiberglass bonded with urea-formaldehyde resin. The mat is then coated with asphalt
which contains mineral fillers and makes the fiberglass shingle waterproof.
Fiberglass reinforcement was devised as the replacement for asbestos paper
reinforcement of roofing shingles and typically ranges from 1.8 to 2.3 pounds/square
foot.

The older asbestos versions were very durable and hard to tear, an important
property when considering wind uplift of shingles in heavy storms. Fiberglass is
slowly replacing felt reinforcement in Canada and has replaced mostly all in the
United States. Widespread hurricane damage in Florida during the 1990s prompted
the industry to adhere to a 1700 gram tear value on finished asphalt shingles.

A newer design of fiberglass asphalt shingle, called laminated or architectural, uses
two distinct layers which are bonded together. Laminate shingles are heavier, more
expensive, and arguably more durable than traditional shingle designs. Laminated
shingles also give a more varied, contoured visual effect to a roof surface.

[edit]   Durability
Asphalt shingles usually last longer in cooler climates than warmer ones. Thermal
shock is one thing that is damaging to shingles (thermal shock is what roofing
materials experience when the ambient temperature changes dramatically within a
very short period of time). Another factor affecting asphalt shingle roofs is attic
ventilation. Proper roof ventilation has been known to extend the service life of a
roof. Shingles should not be applied during cold weather. Each shingle must seal to
the layer below it to form a monolithic structure. Sun and heat to soften the
underlying exposed asphalt is a requirement during the initial phase of a new roof.
Staple guns should not be used on shingles because they tear into the substrate too
easily. Traditional roofing nails remain the best method of applying shingles.



ASPHALT ROOFS: This is the most commonly used and least expensive roof covering
material. Asphalt roofing materials consist of either a rag fiber or a fiberglass mat impregnated
with asphalt and covered with colored mineral granules. A wide variety of designs, weights,
colors and sizes are available.

Asphalt roofs show their age when the mineral granules wear off, reveal the black asphalt and
the corners and edges of the shingles begin to curl and crack. This is an indication that the
asphalt composition has begun to dry out and lose its weather-proof seal. When only a few
shingles show the above type of wear, the simple and less costly replacement of worn out
shingles may be all that is needed. If one out of every five to ten shingles shows this wear and
aging, it is may be time to re-roof.

WOOD SHINGLES AND SHAKES: Shingles made of cedar, cypress or red wood are highly
rot-resistant and may last 30 to 35 years if properly installed and maintained. The best wood
roofing materials are pressure-treated with wood preservatives. When considering home safety, it
is wise to note that wood shingles and shakes are more highly combustible than the other roofing
materials available. If a wood shingle is your choice, look for one treated with fire-retardant
chemicals.

As wood shingles and shakes age they may shrink and form gaps between each shingle. They
may also become brittle and offer less protection from the elements. As is the case with asphalt
shingles, if only a few wooden shingles show this wear and tear, replace the individual shingles.

Laminated fiberglass shingles: These are similar to asphalt shingles and do contain many of the
same materials, but they are thicker and more durable and give a much nicer texture to your roof.
They can cost twice as much but do last longer...up to thirty years.

METAL ROOFS: Metal roofs are highly resistant to damage from the elements and may
frequently last 40 years or more. They are highly fire resistant and require little maintenance.
Small damaged areas can be repaired with patches of similar metal. The materials used in a metal
roof may include copper, tin, steel, aluminum, lead or an alloy combination of one or more of
these metals.

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. While its insulating properties were poor, its
low cost and easy application made it the most accessible commercial roofing, world wide. 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.

 The increase in regeneration schemes throughout the country has contributed to the higher
demand for roofing products, particularly steel roofs. Mixed-use developments have overtaken
pure housebuilding, and the trend is to bring visual coherence to the different elements of a
scheme by roofing them in matching materials. steel roofs have had a greater increase in market
share than any other roofing material over the past five years.

Aluminium



TILE, SLATE AND COMPOSITES: Roofs made of slate or tiles composed of either clay or
concrete are perhaps the longest lasting available. They frequently survive more than 50 years,
and normally require little or no maintenance. In addition these materials are extremely fire
resistant. When one of these roofs does need replacement, however, the cost can be very high.

Tiles offer comparable benefits to slate but come in a more decorative and cosmetically-pleasing
variety of colors, textures, shapes and sizes. Tiles can be glazed or unglazed. Slate typically
comes in only black, grey or dark red.

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 USA, 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.

Asbestos shingles
Pitched roof covering : -

As already stated, pitched roofs are usually covered with tiles or slates which fix, or clip over,
battens. These battens sit on a roofing membrane and are fixed to the rafters below. The battens
are fixed at regular intervals according to the gauge (distance between battens) specified by the
tile manufacturer. This in turn will vary according to the angle, or pitch, of the roof.

Each tile must overlap the tile below it




Cameroon, a wattle and daub house, roofed with banana leaves.




Japan, rice straw thatch
England, slate




Hungary, terracotta tiles




[edit] Drainage




The flat roofs of the Middle East, Israel.




The steeply pitched, gabled roofs of Scandinavia.
The overhanging eaves of China.

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 is of a highly impermiable 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.

				
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