ROOFING SYSTEMS - 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. 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 lose heat in cold climates. Clay tiles are a traditional kind of roofing material. Wooden shingles are light and easily replaceable, and were used extensively in many parts of the world.

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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.

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.

Metal Roofing Systems: metal roofing systems are hugely popular in today's times.

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

This a site that explains the art and science of building construction in great clarity and detail.  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 and design offices.  This expert knowledge of building construction is not available in textbooks!
We also take great pains to ensure that our quality of writing is of a high standard.  We aim to take complicated situations and make them simple and clear, as well as to provide content that is interesting to industry experts and newcomers alike.  Do let us know where we succeed - and where we fail - in this task.

http://www.understandconstruction.com/roofing-systems.html

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ASBESTOS - Asbestos is found in heat and acoustic insulation, fire proofing, and building materials like roofing and flooring; in older automotive parts like disc brake pads and drum brake linings, which used asbestos because of its friction properties. Natural weathering or human disturbance can break down naturally occurring asbestos into fibers that can be inhaled and cause respiratory diseases. By covering naturally occurring asbestos with clean soil or planting grass, you can reduce your exposure.

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Asbestos

How Asbestos Works

 BY TIFFANY CONNORS 

If asbestos is such a danger, and we've been removing it since the 1980's, shouldn't it all be gone by now?

You would think so, but even though it seems like we've had a lot of time to get it out of our homes, schools and workplaces, asbestos has been around for 3,000 years, so it's had a head start.

Getting rid of asbestos isn't as easy as changing your clothes. Besides, it's not such a villain as long as it isn't disturbed.

Asbestos hasn't been produced in the United States since 2002.

However, the United States still imports approximately 3,000 tons per year, and there are plenty of older buildings where asbestos still resides [source: Asbestos Project Plan].

Why? Because removing it can be more dangerous than leaving the original substance intact; if it's properly sealed and left undisturbed, asbestos doesn't pose a danger to us.

Asbestos is in fact a naturally occurring substance, so we're all exposed to some degree. The difference between most people and the danger zone is the amount of exposure.

With asbestos, the problem comes when we inhale the fibers.

And while we exhale a lot of them right back out of our system, some of the fibers can stick around and scratch our lungs, causing scarring and inflammation that can lead to a variety of serious respiratory diseases.

These fibers, which are used in construction materials because of their durability, build up over time and are strong enough to stay in our lungs forever.

So even though we may feel fine now, the same fibers we breathe in today could give us cancer 30 years from now.

But what exactly is asbestos? And how can we protect ourselves and our loved ones from its dangers? In this article, we'll explore asbestos and what you need to know.

What Does Asbestos Look Like?

In most commercial forms, asbestos looks like attic insulation -- a ball of thick fuzz. The individual asbestos fibers that are released into the air are microscopic.

The U.S. government defines asbestos as a naturally occurring group of fibrous minerals that are very strong, can be woven, and resist heat and most chemicals [source: EPA].

The current federal definition includes these classes of asbestos:

·   Chrystotile

·   Amphibole (with subsets:crocidolite, amosite, anthophyllite, tremolite and actinolite)

While both chrystotile and amphibole are known to cause respiratory diseases, the more durable, thinner strands of amphibole asbestos are considered more dangerous and more likely to cause mesothelioma (a form of cancer caused by asbestos) because they tend to stay in the lungs longer [source: Agency for Toxic Substances and Disease Registry].

However, the more flexible chrystotile asbestos is used in about 95 percent of all asbestos in commercial products and is still considered carcinogenic [source: Encyclopedia Britannica].

Asbestos has been used for thousands of years, dating as far back as the ancient Greeks.

Its durability and ability to withstand heat and erosion made it attractive to builders, and it was even used in some clothing because of its fire -resistant qualities. Modern asbestos production began in 1868 through mining deposits [source: Encyclopedia Britannica].

Reports of long-term harmful effects of asbestos exposure began appearing in the 1970s, although dangers associated with asbestos were suspected decades earlier.

In 1989, the U.S. government issued a ban on products containing asbestos. This regulation was overturned in 1991, but certain products were still banned, as were "new uses" of asbestos [source: EPA].

Where is Asbestos?

The fact is, we're all exposed to asbestos, although usually in such small quantities that it poses no threat.

The typical air concentration of asbestos fibers is 0.00001 to 0.0001 fibers per milliliter.

In comparison, U.S. workplaces are limited to exposing employees to 0.1 fiber/mL, and significant exposure is considered years of exposure to 0.125 to 30 fibers/mL [source: Agency for Toxic Substances and Disease Registry].

In nature, the fibrous asbestos is embedded in rocks, most commonly ultramafic rock (a type of igneous rock), which is found in much of California and near fault zones. Not all ultramafic rock contains asbestos, but all ultramafic rock has the potential to contain veins of asbestos [source: Agency for Toxic Substances and Disease Registry].

Mining areas in the eastern United States have also been discovered to contain naturally occurring asbestos.

To obtain the asbestos for use -- and to make it airborne -- the rock must be crushed to release the fibers.

In commercial products, asbestos is still found in heat and acoustic insulation, fire proofing, and building materials like roofing and flooring.

Additionally, asbestos can be found in older automotive parts like disc brake pads and drum brake linings, which used asbestos because of its friction properties [source: Asbestos Project Plan].

Banned new products include flooring felt, cement shingles (also known as asbestos siding), and corrugated, commercial and specialty paper. However, older material that used asbestos can still be found widely [source: EPA].

Asbestos testing should be conducted by licensed government agencies, and trained asbestos abatement professionals should be the only ones performing the removal.

In some cases, it's safer to seal the asbestos in rather than remove it.

For more information on getting asbestos out of your house, see Is it safer to remove asbestos from a building or leave it there?

In cases of emergency asbestos exposure – when Hurricane Katrina hit New Orleans or the fall of the World Trade Center, for example -- the best thing to do is get out of the area (keeping your mouth and nose covered with a wet cloth when possible) and contact your state and local agencies or the Environmental Protection Agency for more information on proper testing, removal or containment.

Now that you know what and where to look for asbestos, we'll talk about warning signs to watch out for if you've been exposed to asbestos.

WHAT IF I FIND NATURALLY OCCURRING ASBESTOS?

Natural weathering or human disturbance can break down naturally occurring asbestos into fibers that can be inhaled and cause respiratory diseases.

If you live in an area where naturally occurring asbestos has been disturbed, avoid unpaved surfaces, and wet any dirt before digging [source: Agency for Toxic Substances and Disease Registry].

By covering naturally occurring asbestos with clean soil or planting grass, you can reduce your exposure. And be sure to contact your local government for safe removal [source: EPA].

Diseases and Symptoms Associated with Asbestos Exposure

So you've been exposed to asbestos; how likely are you to get sick? Diseases from asbestos exposure take a long time to appear.

The typical range is 10 to 40 years after exposure, although it depends on the type of illness as well as other factors, such as whether the patient is a smoker (which increases the probability of the person developing respiratory ailments).

The concentration, duration and frequency of asbestos exposure also has a hand in determining your chances of developing an illness.

The long and thin fibers of amphibole asbestos are more likely to reach the lower airways and inflame the lungs and pleura, the membrane that lines the lungs [source: Agency for Toxic Substances and Disease Registry].

The three most common illnesses associated with asbestos exposure are lung cancer. Asbestosis and mesothelioma. All three share the common symptom of difficulty breathing.

Lung cancer causes the most deaths due to asbestos exposure, although asbestos exposure is not the only culprit [source: EPA].

Common symptoms include coughing, chest pains, hoarseness and anemia.

Asbestosis is the result of asbestos scratching and scarring lung tissue. It usually shows up the earliest of all the respiratory ailments -- typically 10 to 20 years following exposure [source: Agency for Toxic Substances and Disease Registry].

A common symptom is a dry, cracking sound in the lungs while inhaling.

Mesothelioma is a rare cancer that affects the pleura. The majority of mesothelioma cases are due to asbestos exposure [source: Mesothelioma].

It may take years to develop, and may resemble pneumonia. Some common symptoms include chest pains and a persistent cough.

If you think you may have an asbestos-related respiratory illness, consult a pulmonary physician immediately.

https://home.howstuffworks.com/home-improvement/household-safety/asbestos.htm

ASBESTOS FIBERS - Elevated concentrations of airborne asbestos can occur after asbestos-containing materials are disturbed by cutting, sanding or other remodeling activities. Improper attempts to remove these materials can release asbestos fibers into the air in homes, increasing asbestos levels and endangering people living in those homes.

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Airborne Asbestos Fibers

Asbestos' Impact on Indoor Air Quality

Asbestos is a mineral fiber that occurs in rock and soil.

Because of its fiber strength and heat resistance it has been used in a variety of building construction materials for insulation and as a fire-retardant.

Asbestos has been used in a wide range of manufactured goods, mostly in:

·   Building materials:

·   Roofing shingles

·   Ceiling and floor tiles

·   Paper products

·   Asbestos cement products

·   Friction products:

·   Automobile clutch

·   Automobile brake

·   Transmission parts

·   Heat-resistant fabrics

·   Packaging

·   Gaskets

·   Coatings

Elevated concentrations of airborne asbestos can occur after asbestos-containing materials are disturbed by cutting, sanding or other remodeling activities.

Improper attempts to remove these materials can release asbestos fibers into the air in homes, increasing asbestos levels and endangering people living in those homes.

https://www.epa.gov/indoor-air-quality-iaq/asbestos-impact-indoor-air-quality