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Roofing
Systems
understandconstruction.com
In this article,
when we say "roof", we mean a sloped cover to a building, made of any
material, and we do NOT mean a flat concrete slab that can be used by humans.
Let’s start with a
well-kept secret, one that will give you an instant instinctive grasp of how
the range of roofing solution works:
"the slope of
the roof is a clear indicator of how hi-tech the roof is. A very low
slope will mean a hi-tech roof, and a high slope a low-tech roof."
To understand this
principle, let us start with one of the most low-tech roofing systems: a thatch
roof.
Thatch roofs in
most countries will have a slope of 45 degrees or so. This is because they are
not very watertight.
However, they are
rather thick, most often 400mm (16") or so. So the high slope forces the water
to run off before it penetrates through the thickness of the thatch, a
low-tech solution.
On the other hand,
a state of the art system such as low-slope "kliplock" corrugated
metal sheeting can be installed at slopes of 1 degree or less, as it is perfectly
watertight.
Take a look at the
image below, which shows the correct slopes for a range of roofing systems, to
understand this in greater detail.
Apart from being
watertight, a roof must perform other functions: it must support snow, must
look attractive, must have a permanent abrasion-resistant finish, must not
absorb heat in hot climates, and must not loose heat in cold climates.
A roof must be able
to withstand the following loads:
· wind loads, which can be very large in some areas
· human loads (if the roof is not accessible, it must be able to
withstand the weight of maintenance workers)
· snow loads
· earthquake
For a number of
reasons, the image of a building with a sloped roof has very strong roots in
the human psyche - you will even find this on your browser, to denote a
"home" page.
TYPES OF ROOFING SYSTEMS
A thatched cottage in England. Note that the ridges of the roof form have been given additional layers of thatch protection, and that this has been turned into a beautiful decorative element! |
Thatch Roofs: are one of
the earliest roofing systems created by man, and are still used in millions of
structures worldwide.
Made of dried plant
stems, a thatch roof will commonly have a slope of 45 degrees and
thickness of 400mm (16").
This thickness is
made up of a number of layers of individual plant fibres.
When water falls on
a thatch roof, it will trickle from layer to layer as gravity pulls it
downwards.
The thickness
actually creates sufficient layers for the water drops to move horizontally out
of the structure before they fall into a room.
The steep slope
serves to increase the speed of the drops, so that they quickly move out of the
structure before falling inside.
This kind of roof is very different from other roofs, as it does not have a single watertight skin, but has instead a large number of partially waterproof layers.
Slate or Stone
Roofs: stone is not the greatest material for roofs, as it is
heavy. A slate roof being installed over wooden battens.
Slate is a naturally occurring type of stone
that splits into thin layers if you hit it with a chisel in just the right way.
This produces thin, waterproof tiles that can
be overlapped to form a roof.
Since the stone tiles are not exactly the
same size and thickness, this is not a system that is highly waterproof.
Therefore, it needs to have a good slope, of
say 20 to 30 degrees, to force the water to run off the roof and
not trickle through the gaps.
A traditional southern mediterranean style clay tile roof. |
Clay Tile Roofs: clay tiles
are a traditional kind of roofing material.
Clay is a material that is both widely
available and easy to shape into forms that have lips and channels to direct
the flow of water.
It is still widely used in many parts of the
world, and has an attractive appearance.
Wood Shingle Roofs: wooden
shingles are light and easily replaceable, and were used extensively in many
parts of the world.
Corrugated metal roof sheeting is inexpensive
and quick to install.
It works best for the very large roofs of
factories, stadiums, and airports, but can also be used in any type of
building, including houses.
They are used in
almost every industrial and airport terminal building and can also be used in
residential and educational buildings.
They make for an
extremely light, strong, economical, and waterproof roof, and come in a very
wide range of varieties.
Commonly used
metals are mild steel, aluminum, and stainless steel.
Steel roofing
sheets need to be protected from corrosion, and are usually galvanized or coated with other
protective layers.
The sheets are
quite thin, as much as 0.5mm in the case of steel, and 1mm in aluminum.
They therefore
require insulation and other layers to be incorporated into the roof.
Asphalt Shingle Roofing: this is a modern,
"man-made" solution.
Asphalt shingles are actually thin
rubber-like sheets that are cut to look like clay or stone shingles.
They are usually stuck onto the under-surface
with an adhesive, or with hot bitumen.
Learn everything about building construction
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Our goal is to make you understand concepts in building
construction.
Written by architects and engineers, the content on the site is actually a
result of accumulated years of work experience at building construction sites
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simple and clear, as well as to provide content that is interesting to industry
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http://www.understandconstruction.com/roofing-systems.html
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