The use of steps and stairs by pedestrian traffic is thought to pose a greater risk to pedestrian safety than walking on level ground, as the consequences of a slip or fall are likely to be far more serious. Workplace accidents involving slips, trips or falls on stairs reported to HSE are not classified as stair accidents, due to a limited number of ‘Kind of Accident’ categories currently in use. Stair accidents cannot be classified as ‘Slips, trips and Falls on the Same Level’, and so are generally grouped within the ‘Falls from a Height’ category. Recent HSE statistics show that ‘Falls from a Height’ were the largest cause of fatal injuries and the second highest cause of non-fatal major injuries in 1998/99 (provisional figures). Recent ‘non-workplace’ statistics for injuries in the home suggest that the annual number of stair accidents in the UK is roughly equivalent tothe number of slips, trips and falls on the same level (both ~250,000) (indeeed, recent statistics (The Architects Journal, 22.6.00, source: DTI) show that around 1000 pedestrians are killed through domestic stair accidents in the UK per annum). It is therefore reasonable to suggest that stair accidents account for a large proportion of the ‘Falls from a Height’ accidents reported to HSE. HSE’s understanding of workplace slips and trips is growing, but very little is currently known about the risks associated with staircase use, the assessment of the associated risks, and means of stair accident prevention.

Boycott the elevator. Walking up stairs for an average of six minutes a day will lower your cholesterol by 10 to 15 percent - and make you 10 to 15 percent fitter, according to a new study at the University of Ulster at Jordanstown.

Professor Colin Boreham and his team have found that bursts of short, intermittent exercise - like climbing a few flights of stairs - can lower cholesterol.

They conducted a seven-week study into the effect of stair climbing on the fitness levels of 22 sedentary women.

We measured the women’s height, body mass, heart rate, blood lipids and oxygen uptake before, during and after the programme, said Professor Boreham.

The major findings were the important indicators of cardiovascular fitness and health, were enhanced by the stair climbing exercises. The programme also resulted in beneficial effects on the women’s cholesterol levels.

What is intriguing is that these improvements came as a result of really very little exercise, said professor Boreham.

The women only did a maximum of 13 minutes of stair climbing per day over the seven week research programme - and even those 13 minutes were not done all at once.

Stair climbing is a particularly efficient way of incorporating health-promoting exercise into an individual’s lifestyle.

You don’t need to go to a gym, or have to change clothes, or any of the time-consuming things associated with traditional gym-based exercise routines, he said.

It is a message that will be warmly welcomed by figure conscious people everywhere.

Objectives

The overall aim of this project is to improve the safety in use of non-domestic and domestic stairs. The specific objectives are - to determine the potential of slip resistant nosings to reduce the risk of injuries associated with slips on stairs - to highlight additional hazards that might be introduced by including slip resistant nosings on stairs and provide guidance as to the best practice for safer stairs - to investigate the benefit of nosing profiles for the ambulant disabled, including those designs shown in Approved Document M and draft BS 8300 (also to investigate the benefit of the traditional nosings used on domestic timber stairs, with and without carpet coverings).

Description

This project is required to meet DETRs objectives of promoting innovation & culture change, business improvement, construction process improvement, social impact, best practice, sustainability and to address safety & health issues in the construction sector as described in Prospectus 2000. The Priority Area and Theme relevant to this project are Evaluation of Risks to Safety and Health, Social Impact Theme. The results from this project will determine the effect of stair nosings on stair accidents and provide best practice guidance on stair nosing design. Current practice for building managers and building planners is to apply proprietary nosings to all stairs where there may be a risk of falls, and hence injuries, to the public or to the workforce. These nosings were originally designed to protect carpet from wear in use, as the nosing area is easily worn where there is substantial pedestrian traffic on stairs. They have subsequently taken on the appearance of a safety device by including slip-resistant properties into the materials used for the nosings. There is however no evidence that these devices provide safer conditions for users and in some cases have been known to introduce new risks to the users. The materials are known to have slip resistant properties but these apply to walking on the level only (the gait applied when walking on the level is different to walking on stairs). It is believed that most accidents that occur when descending stairs occur because of overstepping rather than slipping on the tread. The type of material on the nosing edge may have an influence on such accidents, either preventing them or potentially increasing the likelihood of harm by causing the victim to fall forward rather than backwards if the fall occurs during descent. Nosings on stairs with short treads can present a hazard to people descending the stairs as the effective width of the tread is reduced and heels may catch on the nosings. Protruding nosings may also present a hazard to some people ascending the stairs, including the ambulant disabled, where the foot is dragged up the riser, the toe may catch on the nosing. Slightly rounded leading edges allow for light modelling for better visibility and will reduce injuries if one should fall against the tread. There is also the question of the shape of the leading edge, which should not have such a large radius that there is a tendency to slide over the edge. Approved Document M and draft BS 8300-2:Section 8 give guidance on profiles for risers and key stair dimensions. The validity of this guidance should be verified. Guidance exists in Approved Document M on nosings for the ambulant disabled. This and other guidance should be evaluated in order to determine the need for amendments to Approved Documents K or M. This should include the dimensions of nosing and guidance on colour, luminance and contrast for visually impaired users. The work will follow as an extension to an existing project that is jointly funded by the Health & Safety Executive. The existing project is assessing the safety of different goings on stairs. The new project will extend the work to include nosings in a variety of environments, including non-domestic and residential (housing) properties. It will also assess the existing guidance contained in Approved Document M, Access and facilities for disabled people, regarding the profile of nosings.

Summary of results

1. This project undertook practical trials on a variable going stair rig to determine the potential for slips, trips and falls on stairs with different going size, stair material and surface contaminants. It also examined the use of different proprietary nosings and the potential missteps that might occur in an overstep situation. The final report drew together the results from this project and from earlier work (CC1570, 1994 and 1997) and presented recommendations for changes to Approved Documents K and M. These are summarised as: - an increase in the minimum going for private and public stairs - a decrease in the maximum rise for private and public stairs - a maximum difference between successive goings on a flight - introduction of the concept of acceptable and non-acceptable handrails - an increase in the height of stair guarding, and extension of handrails beyond top and bottom nosings - definition of the maximum pitch for dwelling stairs - definition of the minimum clear stair width at handrail height in dwellings - the adoption of closed risers in dwelling stairs - the banning of winder flights in dwellings In addition the project produced valuable guidance on choosing the right proprietary nosings for non-domestic stairs.
   These are summarised as:
   - an increase in the minimum going for private and public stairs
   - a decrease in the maximum rise for private and public stairs
   - a maximum difference between successive goings on a flight
   - introduction of the concept of acceptable and non-acceptable handrails
   - an increase in the height of stair guarding, and extension of handrails beyond top and bottom nosings
   - definition of the maximum pitch for dwelling stairs
   - definition of the minimum clear stair width at handrail height in dwellings
   - the adoption of closed risers in dwelling stairs
   - the banning of winder flights in dwellingsIn addition the project produced valuable guidance on choosing the right proprietary nosings for non-domestic stairs

It may come as a surprise that as long ago as 1992 The Guardian listed John Templer’s work The Staircase as one of its publications of the year. The depth of information and research that the book contained also prompted The Los Angeles Times to write a double page article about it. Now an acknowledged source of reference, it draws attention to an element of construction which continues to present a health and safety problem.

Of the many statistics about slips, trips and falls, perhaps the most poignant is that they account for around a quarter of all major injuries in the workplace. Running and walking injuries are not, industry specific. In schools, where pupils tend to be oblivious to hazards, there has been no distinct rate of reduction. In 2005/6, for example, there were 8367 injuries resulting from slips and trips, 5440 of them involving children, and 1357 involving employees. The statistics are much the same whether you look at further/higher, secondary and primary education.

Construction associated accidents attributable to slips and trips increased every year between 1997 and 2003, in total by 68%. Falls from height in construction understandably attract attention due to the fatalities and serious injuries which result from them, but the number of ‘over 3-day’ accidents resulting from slips and trips has consistently been greater (1975 compared to 804 in 2005/6).

Requirements for stairs and handrails in buildings other than dwellings, set out in Approved Doc Part M, now mean that handrails must be designed to accommodate all users. They must be continuous and terminate beyond the top and bottom of a flight in a way that reduces risk, for example, of clothing being caught. In addition to being sited either side of a stairway, additional rails to divide the flight into channels not less than 1.0 metre wide takes account of the particular needs of busy environments such as schools. It may not be possible to ensure that rails are used, but narrower isles control traffic flow and place stair users in closer proximity to a point of safety.

In addition to the need for handrails which are continuous to grip, adequate visual contrast must be provided against their background. Research has shown, however, that for the partially sighted, ability to appreciate visual differences is more reliably achieved through a surface’s light reflectance value (LRV) rather than just its colour. In the 2004 edition of AD M and the 2005 amendment of BS 8300, reference to difference in LRV became the preferred way of expressing guidance on visual contrast. Roy Bradburn, Operations Director for the Handrail & Balustrade Division of Laidlaw Solutions Ltd, commented “The LRV is measured on a scale of 0 -100, with jet black equivalent to zero and a perfect white 100. These values, however, are never achieved in practice and the 2005 amendment to BS8300 recognised that visual perception is affected by the relative area of surfaces and whether they are textured, curved, metallic or glossy. BS8300 is shortly to be updated and LRV’s will be almost certainly be covered in greater detail”.

In terms of effective use of handrails, there is some debate about what constitutes an appropriate diameter rail. If the size is to be reduced say to 35mm, risk is greatly increased of hands catching against uprights. In situations where the need exists to resist higher horizontal loads, a 3kN system requires a 60mm (as against a standard 38-40mm) diameter rail anyway.

Infill choice is particularly important as AD K requires buildings likely to be used by children under 5 to be safe against climbing the balustrade guarding. Far greater use of structural glazing has resulted, even in environments such as universities where its use might not be considered essential. Tinted and acid etched glazing provides scope for more contemporary design, but the visual clarity and security which it provides are its greatest attributes. The extent, however, to which structural glazing and handrail and balustrade upgrades will have a positive effect on falls and slips on stairs remains to be seen. The contribution of individual elements can be hard to measure and, as always, the human nature is the biggest potential limiting factor. But as Roy Bradburn concluded “A combination of effective visual, tactile and touch characteristics can only help handrails and balustrades act as a catalyst to a change in safety attitudes. We firmly expect the next round of statistics to reflect the contribution that upgraded handrails is making.”

There are two different classes of stairs. The first class is a mill-made stair, which is usually fabricated in a mill shop and shipped to the job site as a kit, ready for assembly and installation. The second class, a carpenter-built stair, is just that — a stair built on site by a carpenter. This type of fabrication is less expensive and allows the stair to be covered with carpet. A carpenter-built stair can be dressed up with a hardwood or paint-grade skirt board. And simple wall-mounted railing is a popular option to complete either type of stair.

When constructing a stair, functionality is the most important consideration. Extreme accuracy must be used for a safe design. Before beginning construction, you should consult not only the national building-code requirements, but also the local building-code requirements. Some municipalities have stricter codes than others, and checking first will eliminate the need to rebuild later.

After determining the correct code requirements for your stair, consider the stair’s design aspects. Remember, the construction materials that you use will dictate the outcome of your finished product, and quality materials will produce a quality job. Do not mistakenly think that because the material will be covered with carpet and no one will see it, the quality of construction materials doesn’t matter; it does. When you use a lower grade of material that contains knots and voids, the stair may encounter cracking at a later date. Most lumberyards carry stock used specifically for the construction of stairs.

Layouts and Calculations

After you have determined the proper codes to follow for your municipality, you are ready to begin the layout and calculations of your stair. Grab a pencil and commit your plans to paper, sketching a rough blueprint of your staircase.

For the purpose of this example, this project will be a straight stair. The building code that we are implementing for this project is BOCA 96 for residential use. This code states that you may have a maximum riser height of 7 3/4 inches and tread run of no less than 10 inches.

First determine the size of your stairwell, making sure to allow for the proper headroom to accommodate the stairs. Headroom is very important; you need to be able to ascend and descend the stair safely. Many a stair has been torn out due to incorrect calculation of this item before the stair is built and installed. There is nothing worse than having some common stair-building sense knocked into you by bumping your head. For this example the nosing will be a standard 1 1/4 inch, the tread run will be 10 inches each, and the headroom will be 6 feet, 8 inches

Assuming the distance from one finished floor to the other (total rise) measures 118 inches, find out the number of risers needed by dividing the total finish rise by 7.5. The resulting number equals the number of risers. Then divide that number into the total finish rise.

Example:  Total rise 118”/ 7.5 = 15.73  — round up the total number of risers to 16

                  Total rise 118”/16 risers = 7 3/8” each rise

Knowing the number of risers tells you the number of treads — 15 (the sixteenth riser will be positioned approaching the upper floor with no tread on top). The run of the stair will then be 15 treads at 10 inches per tread, or 150 inches of total run. To determine the actual total length of the stair, you must add the nosing of the bottom step and the thickness of the top riser.

Example:  Total tread run 150” + 1 1/4” nosing + 3/4” top riser = 152” total stair length

Next, calculate the length of the stairwell, or the width of the upper floor’s vertical shaft in which the stairs are located. This is a two-step calculation.

First, account for the required headroom and the upper-floor construction, including floor-joist height, floor thickness and drywall thickness. For the purpose of our example we will calculate the upper-floor construction to be a total thickness of 12 1/2 inches. This figure (12 1/2 inches) added to the desired headroom height of 80 inches will total 92 1/2 inches. Take this dimension and divide it by the riser height.

Example:  92 1/2” / 7 3/8” = 12.542 

The answer you get (12.542) is the number of treads needed in the clear opening to make headroom. This would mean that you now have 2.45 treads that are located under the header.  By multiplying 12.542 (number of treads in clear opening) by 10 inches (tread depth dimension) and adding 1 1/4 inch for the nosing and 3/4 inch for the top riser, you will achieve the stairwell length needed for the proper headroom. The result for our example is 127 7/16 inches for stairwell length.  Most stairs that are located between two walls have a finished width of 36 inches. To accommodate this finished width you will need to make your rough opening 37 inches.

The end result of our layout procedure is: 10” run, 7 3/8” rise, 127 7/16” stair well length, 37” stair well width, 36” stair finish width. 

Wood glues are adhesives used to tightly bond pieces of wood together. Many substances have been used as glues.

The most common wood glues are polyvinyl acetate (PVA), also known as “white glue” or “hobby and craft”, and aliphatic resin emulsion, commonly referred to as “carpenter’s glue” or “Yellow glue”, which has similar relative ultimate strength. The two have different grip characteristics before initial set, with PVAs exhibiting more slip during assembly and yellow glue having more initial grip. Traditionally, animal glues were ubiquitous, especially hide glue, which is still used in lutherie and restoration. Polyurethane glue (trade names include Gorilla Glue and Excel) is becoming increasingly popular, especially where water resistance is required, although water-resistant cross-linking PVAs are available.

Other substances used as wood glue include

• Cyanoacrylate (Crazy glue or Superglue) used mainly for small repairs, especially by woodturners;
• Contact Cement for veneers;
• Hot melt for temporary uses;
• Epoxy mainly for exterior uses;
• Other synthetic resins including resorcinol, urea-formaldehyde, phenol formaldehyde resin, etc;
• Homemade glue for paper, wood, and internal uses.

Wood glue bonds tightly to wood, but not to itself. Therefore, woodworkers commonly use surprisingly little glue to hold large pieces of wood. Most wood glues need to be clamped while the glue dries.

• Wood glue is also one of the most effective household and industrial products to use as a facial mask. The ingredients it contains are highly beneficial to clarifying and removing dead skin cells, dirt and any other impurities that cause acne. One major benefit is its chemical properties allow it to be used on all skin types. Considering its thick consistency and viscosity, water must by added to dilute the strong bonds in order for it to be pliable and easy to spread over the face. As with all other face masks, it should be left on for no longer than 20 minutes.

Polyvinyl acetate (PVA or PVAc) is a rubbery synthetic polymer. It is prepared by polymerization of vinyl acetate monomer, also referred to as VAM. Partial or complete hydrolysis of the polymer is used to prepare polyvinyl alcohol. Hydroylized alcohol product is typically in the 87% to 99% range (converted PVA). It was discovered in Germany by Dr. Fritz Klatte in 1912 with the help of his assistant James Michael Fairholm.

As an emulsion in water, PVA is sold as an adhesive for porous materials, particularly wood, paper, and cloth. It is the most commonly used wood glue, both as “white glue” and the yellow “carpenter’s glue.” PVA is widely used in bookbinding and book arts due to its flexibility, and because it is non-acidic, unlike many other polymers.

PVA is a common copolymer with more expensive acrylics, used extensively in paper, paint and industrial coatings, referred to as vinyl acrylics. It can also be used to protect cheese from fungi and humidity. It is slowly attacked by alkali, forming acetic acid as a hydrolysis product. Boron compounds like boric acid or borax will form tackifying precipitates by causing the polymer to cross-link.

PVA is also commonly recommended for use in making leather handcrafted works and papier-mâché.

Medium-density fibreboard (MDF or MDFB) is an engineered wood product formed by breaking down softwood into wood fibers, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure.

It is made up of separated fibers, (not wood veneers) but can be used as a building material similar in application to plywood. It is much more dense than normal particle board.

The name derives from the distinction in densities of fiberboard. Large-scale production of MDF began in the 1980s.

Types of MDF

There are different kinds of MDF, which are sometimes labeled by colour:

• Moisture-resistant is typically green
• Fire-retardant MDF is typically red

Although similar manufacturing processes are used in making all types of fiberboard, MDF has a typical density of 600-800 kg/m³ or .022-.029 lbs/in³, in contrast to particle board (160-450 kg/m³) and to high-density fiberboard (600-1450 kg/m³). Formaldehyde resins are commonly used to bind MDF together, and testing has consistently revealed that MDF products emit formaldehyde and other volatile organic compounds that pose health risks at sufficient concentrations, for at least several months after manufacture. Whether these chronic emissions reach harmful levels in real-world environments is not yet fully determined.

Another addition to the MDF range is a product named FX-Platform, produced by Norbord. It is a softwood plywood core, laminated on both sides with MDF, giving it working properties containing the advantages of both plywood and MDF.  This product has met the acceptance criteria for compliance with the ANSI/HPVA HP-1-2004 Section 3.12 Formaldehyde Emission Requirements for industrial panels.

Lighter densities of fiberboard are commonly marketed as ultralight or LDF boards.

 Manufacture

In Australia the main species of tree used for MDF is plantation-grown radiata pine but a variety of other products have also been used including other woods, waste paper and fibers.

The trees are debarked after being cut. The bark can be sold for use in landscaping, or burned in on-site furnaces. The debarked logs are sent to the MDF plant where they go through the chipping process. A typical disk chipper contains 4-16 blades. Any resulting chips that are too large may be re-chipped; undersized chips may be used as fuel. The chips are then washed and checked for defects.

The chips are then compacted using a screw feeder, and will be heated for 30-120 seconds to soften the wood; they are then fed into a defibrator which maintains high pressure and temperature. The pulp that exits from the defibrator is fine, fluffy, and light in weight and in colour.

From the defibrator the pulp enters a blow line where it is joined with wax (to improve moisture resistance) and resin (to stop the pulp from forming bundles). The material expands in size and is then heated by heating coils. When it comes out it may be stored in bins for an indefinite length of time.

After this drying period the board goes through a “Pendistor” process which creates 230-610 mm thick boards. Then it is cut and continues to the press. Here it is pressed for a few minutes, to make a stronger and denser board.

After pressing MDF is cooled in a star dryer, trimmed and sanded. In certain applications, boards are also laminated for extra strength.

The Environmental Impact of MDF has greatly improved over the years.Today many MDF boards are made from a variety of materials. These include other woods, scrap, recycled paper, bamboo, carbon fibers and polymers, steel, glass, forest thinning and sawmill off-cuts.

As manufacturers are being pressured to come up with greener products, they have started testing and using non-toxic binders. New raw materials are being introduced. Straw and bamboo are becoming popular fibers because they are a fast growing renewable resource.

 Comparison to natural woods

Benefits of MDF:

• Is an excellent substrate for veneers.
• Is becoming an environmentally friendly product.
• Some varieties are less expensive than many natural woods
• Isotropic (no grain), so no tendency to split
• Consistent in strength and size
• Flexible. Can be used for curved walls or surfaces.
• Shapes well.

Drawbacks of MDF:

• Heavier than plywood or chipboard (the resins are heavy)
• Swells and breaks when waterlogged
• May warp or expand if not sealed
• Contains urea-formaldehyde which may cause eye and lung irritation when cutting and sanding
• Dulls blades more quickly than many woods
• Though it does not have a grain in the plane of the board, it does have one into the board. Screwing into the edge of a board will generally cause it to split in a fashion similar to delaminating.
• Subject to significant shrinkage in low humidity environments.

 Recent developments

A fairly recent development is flexible MDF sheets. These are sheets scored with multiple slots so that the material can easily be formed into curved shapes and then fixed. The manufacturer is Bendymdf.

 Applications

MDF is often used in school projects because of its flexibility. It is also often used in loudspeaker enclosures, due to its increased weight and rigidity over normal plywood.

 Safety aspects of MDF

When MDF is cut, a large quantity of dust particles are released into the air. It is important that a respirator is worn and it is cut in a controlled and ventilated environment. It is a good practice to seal the exposed edges to limit the emissions from the binders contained in this material.

Plywood is a type of engineered board made from thin sheets of wood, called plies or wood veneers. The layers are glued together, each with its grain at right angles to adjacent layers for greater strength. There are usually an odd number of plies, as the symmetry makes the board less prone to warping , and the grain on the outside surfaces runs in the same direction. The plies are bonded under heat and pressure with strong adhesives, usually phenol formaldehyde resin, making plywood a type of composite material. Plywood is sometimes called the original engineered wood.

The adhesives used in plywood has become a point of concern, due to the off gassing of the formaldehyde. Both urea formaldehyde and phenol formaldehyde are carcinogenic, so their use is undesirable. Many manufacturers are turning to “Greener Products” as government regulations become stronger against the use of these adhesives.

A common reason for using plywood instead of plain wood is its resistance to cracking, shrinkage, twisting/warping, and its general high degree of strength. In addition, plywood can be manufactured in sheets far wider than the trees from which it was made. It has replaced many dimensional lumbers on construction applications for these reasons.

A vast number of varieties of plywood exist for different applications. Softwood plywood is usually made either of Douglas fir or spruce, pine, and fir, and is typically used for construction and industrial purposes. Decorative plywood is usually faced with hardwood, including red oak, birch, maple, lauan (Philippine mahogany) and a large number of other hardwoods.

Plywood for indoor use generally uses the less expensive urea-formaldehyde glue which has limited water resistance, while outdoor and marine grade plywood are designed to withstand rot, and use a water resistant phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity.

The most common varieties of softwood plywood come in three, five or seven plies with a metric dimension of 1.2 m × 2.4 m or the slightly larger imperial dimension of 4 feet × 8 feet. Plies vary in thickness from 1/10″ through 1/6″ depending on the panel thickness. Roofing can use the thinner 5/8-inch plywood. Subfloors are at least 3/4-inch depending on the distance between floor joists. Plywood for flooring applications is often tongue and grooved. The mating edge will have a “groove” notched into it to fit with the adjacent “tongue” that protrudes from the next board. This keeps the boards from slipping past each other providing a solid feeling floor when the joints do not lie over joists. Tongue & groove flooring plywood is typically 1″ in thickness.

High-strength plywood, known as aircraft plywood, is made from mahogany and/or birch, and uses adhesives with increased resistance to heat and humidity. It was used for several World War II fighter aircraft, including the British-built Mosquito bomber which was nicknamed the wooden wonder.

Certain plywoods do not have alternating plies. These are designed for a specific purpose. One such plywood is known as “Bendy Board”. This is very flexible and is designed for making curved parts. However these may not be termed as plywood in some countries because the basic description of plywood is layers of veneered wood laid on top of each other with the grain perpendicular on each layer.

Other types of plywoods are fire retardant, moisture resistant, marine grade, sign grade, pressure treated, and of course the hardwood and softwood plywoods. Each of these products are designed to fill a need in industry.

In addition to the glues being brought to the forefront, the wood resources themselves are becoming the focus of manufacturers, due in part to energy conservation, as well as concern for our natural resources. There are several certifications available to manufacturers who participate in these programs. FSC certified, Leeds Certified, FSI certified, and Greenguard certified. Many of these programs offer tax benefits to both the manufacturer, as well as the end user.

 Plywood production

Plywood production requires a good log, called a peeler, which is generally straighter and larger in diameter than one required for processing into dimensioned lumber by a sawmill. The log is peeled into sheets of veneer which are then cut to the desired dimensions, dried, patched, glued together and then baked in a press at 140 °C (280 °F) and 19 MPa (2800 psi) to form the plywood panel. The panel can then be patched, resized, sanded or otherwise refinished, depending on the market for which it is intended.

 History

Plywood output in 2005

Plywood has been made for thousands of years; the earliest known occurrence of plywood was in Ancient Egypt around 3500 BC when wooden articles were made from sawn veneers glued together crosswise. This was originally done due to a shortage of fine wood. Thin sheets of high quality wood were glued over a substrate of lower quality wood for cosmetic effect, with incidental structural benefits. This manner of inventing plywood has occurred repeatedly throughout history. Most high quality English furniture makers working in the eighteenth and nineteenth centuries (and since) have used veneering as a technique. In addition to making the most out of the highest quality materials available, it reduces prices and improves stability of construction. The irregularities of grain which confer decorative interest often result in uncontrollable warping and cracking if any attempt is made to use the wood in thicknesses much greater than those characterizing cabinet-making veneers (typically 1-2mm).

Modern plywood, in which the veneer is cut on a rotary lathe from softwood logs, is of relatively recent origin, invented by Immanuel Nobel. The first such lathes were set up in the United States in the mid 19th century. Plywood has been one of the most ubiquitous building products for decades.

One of the earliest applications of mass-produced modern plywood manufacturing in the United States was recorded in Portland, Oregon by the Portland Manufacturing Company. The owner, Thomas J. Autzen helped develop a bonding technology, which greatly shortened the drying and manufacturing process. His early engineering contribution played an important role in making plywood one of the most abundant and affordable building products ever produced.

In India, waterproof plywood is also known as “kitply”. Though Kitply is a brand, it has become a genericized trademark, since the company that makes it pioneered the use of waterproof plywood in India.

The landscape historian John Stilgoe has theorized that the 4′ x 8′ dimensions of a standard sheet are due to the space required for moving a mule into a barn^.

Plywood advantages

1. High uniform strength: Wood is 45 times stronger along the grain than across the grain. Crossing the adjacent sheets tends to equalise the strength in all directions.

2. Freedom from shrinking, swelling and warping: Solid wood exhibits considerable movement across the grain but generally negligible shrinkage or swelling in a longitudinal plane. The balanced construction of a plywood panel with the grain direction of adjacent veneers at right angles tends to equalise stress, thus reducing shrinkage, swelling and warping.

3. Non-splitting qualities: Solid wood splits fairly readily along the grain. Plywood by virtue of the crossed laminations can be nailed or screwed near the edges without damage from splitting.

4. Availability of relatively large sizes: Sawn timber can be obtained in fairly long lengths but only in relatively narrow widths. Plywood can be sold in sizes up to 6 ft * 25 ft and by the scarf jointing of small sheets up to 6 ft *40 ft, however 8 ft*4 ft is the most common size.

5. Economical and effective utilisation of figured wood: Twenty sheets of veneer can be sliced from 1 inch of solid wood. When glued to a core of cheaper material a high grade panel is produced. This procedure thus affects distinct economies in the use of figured or the more valuable woods. In addition to facilitating the utilisation of attractive but fragile face veneers to give results which cannot be duplicated in solid construction. More effective utilisation is obtained by the matching of veneer in such a manner that the decorative effect due to the natural figure in the wood is enhanced by the regularity or symmetry of the design.

6. Ease of fabrication of curved surfaces: The trend of modern architectural design is to feature curved surfaces. The desired shapes can be readily fabricated in plywood construction, utilising male and female forms, or a single forming a vacuum press or autoclave

7. Reduction of waste: One of the important aspects in the manufacture of plywood is that it results in the conservation of timber by the elimination of the waste which occurs in sawing e.g. sawdust. Waste is confined to the small core which remains after peeling, from the veneer which is lost in rounding up the log, and the elimination of such defects as knots and splits.

8. Dense woods can be sliced and bonded into plywood panels for use in furniture construction whereas furniture fabricated from solid timber would be far too heavy.

 US plywood grades

Plywood grades are determined by a veneer quality on the face and back of each panel. The first letter designates quality of face veneer (best side), while the second letter denotes the surface quality of the back of the panel. The letter “X” indicates the panel was manufactured with scrap wood as the center plies, not “exterior” as is commonly thought. The A-D rating is only good for construction (softwood) plywood, not for hardwood plywoods such as oak or maple.

“A”: Highest grade quality available. Can be defect free or contain small knots, providing they are replaced with wooden plugs (the fillers having a “boat” or an “American football” shape) or repaired with synthetic patch. This grade may contain occasional surface splits that are repaired with synthetic filler. The surface is always sanded and provides for smooth paintable face quality.

“B”: Second highest quality veneer grade. Normally a by-product of downgraded “A” quality veneer. Solid surface, but may contain small diameter knots and narrow surface splits. Normally repaired with wooden plugs or synthetic filler. The surface is normally sanded smooth.

“C”: Considered to be a lower end face quality, but a reasonable choice for general construction purposes. May contain tight knots up to 1½ inches diameter, some open knot holes, some face splits, and discoloration. Some manufactures may repair the defects with synthetic filler. Panels are typically not sanded.

“D”: Considered to be the lowest quality veneer and often used for the back surface for construction grade panels. Allows for several knots, large and small, as well as open knots up to 2½ inches diameter. Open knots, splits, and discoloration are acceptable. “D” grade veneers are neither repaired nor sanded. This grade is not recommended for permanent exposure to weather elements. Plywood applications

Plywood is used in many applications that need high-quality, high-strength sheet material. Quality in this context means resistance to cracking, breaking, shrinkage, twisting and warping. Plywood is also used as an engineering material for stressed-skin applications. It has been used for marine and aviation applications since WWII. Most notable is the British De Havilland Mosquito bomber, which was primarily made out of wood. Plywood is currently successfully used in stressed-skin applications. The American designers Charles and Ray Eames and Phil Bolger are famous for their plywood-based furniture