Milled timber, milled wood
Sawn timber is timber that is cut from logs into different shapes and sizes. Sawn timber is generally cut into varying rectangular widths and lengths, but may also be wedge shaped. Common sawn timber products include solid timber beams and more rectangular timber sections.
The first step in the conversion of logs to wood is the preparation of the log. The branches and bark are removed from the tree trunks prior to any processing. Removing the bark leaves all the heartwood, and most of the sapwood. This process now takes place in a matter of seconds on the forest floor with specialised machinery.
Where the logs are to be used as poles or piles, some specifications may call for removal of the sapwood. This can shape the log so that it is perfectly round, has sixteen or more faces, or is true to the original shape of the tree.
Logs classified as ‘saw logs' are sent to a saw mill to be processed. Logs are stockpiled under water sprays to prevent them from splitting as they rapidly dry out.
The logs are then sawn into rectangular shapes in the ‘green mill'. Here the logs are fully saturated and the saws leave a rough surface on the wood, as some of the fibres are torn out rather than cut.
If timber is to be seasoned, or dried, then this will takes place next with the removal of much of the moisture from inside the timber. Seasoned products are then machined to give smooth or shaped surfaces.
Logs present handling difficulties due to their cylindrical shape, so the first steps in a normal saw mill operation involve cutting the logs to provide flat surfaces. There are many different cutting patterns used to produce timber - the following are two examples:
- Splits - the first saw cut is through the centre of the log to give two splits, each of which has a flat face for registering in further cutting operations. A characteristic of splits is that the pith is always on or close to one edge of each of the splits. Some timber cut using this pattern will have the pith on or near an edge.
- Cants - the first saw cuts go either side of the corewood in the very centre of the log. The pieces that are left on the outside are called wings, and the almost-rectangular piece from the centre is called a centre cant. A characteristic of the centre cant is that the pith is always in the centre of a big piece of wood. This is known as ‘boxed heart'. Corewood can cause problems where it is close to one corner or edge. This cutting pattern allows the corewood to be locked into the centre of a reasonable sized section.
Once some flat surfaces have been established by the breakdown saw, the other saws in the green mill can cut the various pieces into marketable timber. Each mill establishes its own cutting patterns for different sized logs, in an attempt to maximise the number of pieces cut in the most popular sizes.
Each cutting pattern produces timber with a distinct appearance and character. Each type has its advantages and disadvantages.
Quarter sawn timber
Also called quarter cutting, with quarter sawn timber the growth rings are parallel to the short face. The long face of every board is close to a radial face. A large number of growth rings can be seen on this face. Quarter sawing timber is best for hardwood species that are prone to collapse during drying.
Quarter swan timber has the following advantages:
- Best grain shows on face
- Good wearing surface for floors, furniture
- Radial face preferred for coatings
- Lower width shrinkage on drying
- Less cupping and warp than other cuts
- Can be successfully reconditioned.
The disadvantages of quarter sawn timber include:
- Slower seasoning
- Nailing on face more prone to splitting.
Back sawn timber
Also known as back cutting and tangential cutting, back sawing is the most common sawing method used in Australia. Back sawing helps to obtain high-grade timber from logs.
Most structural timber and many appearance products are backsawn. With backsawn timber, the long face of each board is close to a tangential face, and the short face is close to a radial face.
Growth rings are parallel to the long edge and the wide face does not intersect many growth rings. The growth rings on the wide face appear to be very wide apart, and some interesting patterns can be seen.
This cut offers more flexibility in that quite large boards can be backsawn from the wings of logs. Here the maximum depth can be just less than the diameter of the log.
Back sawn timber has the following advantages:
- Seasons more rapidly
- Good figure on face
- Less prone to splitting when nailing
- Wide sections possible
- Few knots on edge.
The disadvantages of back sawn timber include:
- Shrink more across width when drying
- More likely to warp and cup
- Collapsed timber more difficult to recondition.
Radial sawn timber
This cut is not very common, and if required would need special negotiation with the mill. However, radial sawing has an efficiency that the other cuts cannot achieve, and makes optimal use of a log.
Because of the cutting pattern, each piece of radially sawn timber is a wedge shape. It has sapwood on the wider edge and pith or corewood at the point.
As real logs are not perfectly round and not perfectly straight, each radially sawn board reflects the longitudinal shape of the log.
These details can make for interesting architectural use of the timber. Apart from flooring, radial sawn timber is used mainly for external applications such as cladding, decking, poles, wedges and timber screens.
Radial sawn timber has the following advantages:
- Dimensional stability
- Less prone to warping, cupping
- Less wastage in milling.
The disadvantages of radial sawn timber include:
- Wedge shaped cross section
- More difficult to detail
- More difficult to stack.
Sawn timber will either be available as unseasoned or seasoned:
- Unseasoned timber - is classified according to its moisture content. Any timber with a moisture content > 25% is said to be unseasoned or ‘green'. However, for practical reasons, most timber sold as unseasoned has a moisture content > 15% rather than the more strict definition of unseasoned timber (> 25%).
- Seasoned timber -producing seasoned timber is the process of drying timber to remove the bound moisture contained in walls of the wood cells. Seasoning can be achieved in a number of ways, but the aim is to remove water at a uniform rate through the piece to prevent damage to the wood during drying (seasoning degrade). Seasoned timber has a moisture content between 10 and 15%. Timber in this condition will be in equilibrium with internal environments in many parts Australia.
Seasoned timber has a reduced weight, improved strength and the cross sectional dimensions remain almost constant. It is more stable than unseasoned timber and is much less prone to warping and splitting. It also provides improved gluing and nail-holding properties and increased joint strength.
In higher grades of timber, particularly hardwoods, the process of seasoning can enhance the basic characteristic properties of timber, increasing stiffness, bending strength and compression strength. Seasoned timber should be chosen for indoor use where it is particularly important not to have shrinkage associated with drying out in service.
Kiln drying timber
The most common commercial processes for seasoning of timber is kiln-drying. Kiln seasoning accelerates the process of seasoning by using external energy to drive the moisture out.
The timber is stacked in much the same way as it is for air drying, and is placed inside a chamber in which the conditions can be varied to give best seasoning results. Air is circulated around the charge (stacked timber) and the temperature and humidity can be varied to give optimum drying. Each species has different cell characteristics and therefore requires different drying schedules. Typically the timber may be in the kiln for a period of between two days to one week.
Generally, it is not feasible to kiln-dry structural timber in thicknesses greater than 45 mm, although there are limited amounts of 70 mm thick kiln-dried softwood members in the market place. All untreated structural pine and some commercial hardwoods are seasoned, mostly using kilns that are often heated by sawmill by-products or gas.
Kiln-seasoning of softwoods such as pine can be done fairly quickly, however seasoning of hardwoods tends to be a much longer process, due to the different cell structure of hardwoods.
The traditional method of seasoning timber was to stack it in air and let the heat of the atmosphere and the natural air movement around the stacked timber remove the moisture. The process has undergone a number of refinements over the years that have made it more efficient and reduced the quantity of wood that was damaged by drying too quickly near the ends.
The basic principle is to stack the timber so that plenty of air can circulate around each piece. The timber is stacked with wide spaces between each piece horizontally, and with strips of wood between each layer ensuring that there is a vertical separation too. Air can then circulate around and through the stack, to slowly remove moisture. In some cases, weights can be placed on top of the stacks to prevent warping of the timber as it dries.
Moisture loss from the side of the wood is at about the correct rate so as not to cause collapse of the cells, but near the ends of the wood, the moisture loss can prove to be too fast. Often the ends are wrapped or painted to slow the moisture loss from the end grain.
While little additional energy needs to be supplied for this type of seasoning, the stacks of timber require a lot of land, represent a potential fire hazard, and the product is not able to be sold for a considerable time.
Air-drying of timber is really a more controlled facilitation of what happens to unseasoned sawn timber, once it is placed into its ‘work' environment. The amount of drying that can occur is decided by the relative humidity of the drying environment and will often vary within individual boards as well as within the stack itself. The time taken for air-drying is a function of the thickness of the timber.
Air-drying is a slow process, particularly for hardwoods, typically taking 6 to 9 months to reach a moisture content in the range 20% to 25%.
A truss is a structure comprising one or more triangular units. Each triangle is constructed with straight and usually slender members of timber, connected at the ends by joints. External loads, and the structure's reaction to those loads, act at the joints, resulting in forces that are either tensile or compressive.
The strength of a truss lies in its triangulation of banding members that work together to the advantage of the overall structure. For trusses, compression members often dictate the size of the elements, thus designs that have short compression members or restraint against lateral buckling are generally more efficient than trusses with longer compression members.
Within a building two forms of trusses can be found. Nail plated trusses are trusses hidden from view that use nail plates as connectors. Architectural trusses refer to those attractively detailed timber trusses, exposed to view. This guide focuses primarily on the application process of the latter.
The benefits of timber trusses are notable and numerous. Timber roof trusses are an ecologically sound choice, compared to conventionally pitched roofs, they use smaller dimension timbers that span greater distances and this in turn reduces the total timber volume contained within. Architectural timber trusses are lightweight, enabling speedy and efficient construction and installation that results that in a visual feature to be enjoyed for decades.
This article provides a comprehensive overview to the processes involved in specifying, assembling and installing an architectural roof truss.
No other cladding material can offer the design freedom, ease of handling, range and natural beauty of timber. Timber cladding can create a building to suit almost any environment, taste or style.
Timber cladding has an inbuilt flexibility that provides natural advantages on sites subject to high winds, extreme climate, highly reactive soils, subsidence or earth tremors. And unlike masonry and other rigid materials, the natural resilience and high strength to weight ratio of timber enables it to withstand far greater stresses and movement.
Modern finishes give a long lasting and attractive appearance to timber cladding and can be used to change the colour and style of the building, making it a versatile material that will keep pace with changing tastes and fashions.
Download the WoodSolutions Technical Design Guide on Domestic Timber Decking here.
Timber decks are a practical and attractive addition to any outdoor landscape. Natural timber decks blend seamlessly with their surrounding environment and will serve as popular entertaining areas all year long.
As an external structure, carrying large loads of traffic, timber decking has high structural performance requirements. In addition decks are usually raised clear off the ground and fully exposed to the weather meaning an effective deck must be able to cope with wear and tear from repeated use and in addition discharge rainwater efficiently. Roundin the corners (easing the arris) of the decking will help run off water while spacing for ventilation between the decking boards will prevent water ponding on the deck surface.
Timber decking is available in both seasoned and unseasoned wood, in a wide range of species, sizes and grades. The natural appeal and strength of timber makes it a practical choice for outdoor decking. This guide provides an overview of best practice methods for specifying, installing and finishing a timber deck.
The inherent appeal and strength of timber makes it the obvious choice for fencing. Timber fencing not only provides a natural look in keeping with the outdoor environment but it also enables the construction of a long lasting, durable property boundary. Fences come in many forms including the traditional paling, picket, post and railing styles. Most rely on a structural frame of posts embedded into the ground and two or more rails spanning between the posts. The ultimate selection of a suitable fence type or style is determined by application and aesthetics. A fence can serve a variety of purposes, including the provision of security, privacy and safety in addition to defining property boundaries. Specification for durability is important, especially for posts, given their exposure to high moisture in the ground.
This section provides an overview to best practice methods in specifying, installing and finishing a timber fence.
Whether for structural or finished flooring applications, timber offers durability, versatility and adaptability. The warmth, strength and natural beauty of timber flooring has proved enduringly popular in a wide variety of interior settings.
Timber flooring is a timeless product, offering a warmth and natural beauty largely unmatched by other flooring options. This article provides an overview of the installation of solid timber strip flooring over bearers and joists, timber based sheet flooring products and concrete slabs. Timber flooring is typically supplied as either solid timber or laminated wood products, made from layers of bonded timber. It fits together with a tongue and groove joint and once in place, is sanded and finished. There is a wide variety of species to select flooring from and the right species for a given application will be dependent on numerous factors. Information relating to species selection, environmental assessment, finish selection and recommended maintenance routines are all provided in this section.
Lightweight timber construction typically comprises framed and braced structures to which one or more types of cladding are applied. Framing configurations can range from the closely spaced light timbers commonly seen in stud frame construction to large, more widely spaced timbers. A timber framed building can be placed on a concrete slab or on posts/poles or bearers resting on piers/stumps supported on pad footings.
Used in houses or multi-residential dwellings, lightweight timber construction offers the flexibility of a wide range of cost effective design options.
When the timber comes from sustainable sources, this construction method can be environmentally advantageous as it combines timber's low embodied energy with its capacity to store carbon.
WOODEN PACKAGING: LOADS OF ADVANTAGES
From pallets to customised packing solutions, timber is a highly flexible, efficient packaging material that delivers value, performance and environmental benefits. As packaging usually uses lower grades of timber, it also optimises log utilisation. Wood consistently delivers value across the supply chain.
Similarly to choosing wood in other applications, using wood packaging can reduce your organisation’s carbon footprint. Wood packaging has two main environmental advantages.
Low embodied energy
The first is that it has low levels of embodied energy, a measure of the man-made energy (usually in the form of fossil fuels) that has been used in its manufacture and transport it to its place of first use.
Lower embodied energy is associated with reduced greenhouse gas emissions and lower energy costs.
Up to half the dry weight of wood is carbon, removed, as CO2, from the atmosphere and stored for life by a growing tree. The carbon stored, or sequestered, in wood packaging is stored there indefinitely - until the wood is burnt or rots.
Reuse and recycling
The average life of a pallet is approximately ten years. During that time they may be repaired or refurbished more than once. A similar process applies to other wooden packaging, including crates, cases, boxes, bins and cable reels.
Once it is no longer vilable to reuse wooden packaging it can be recycled into a whole range of different products or used as bio energy.
Options for end-of-life wooden packaging include:
- Particleboard and other manufactured timber products
- Furniture and other wooden items
- Animal bedding
- Mulch and compost
- Bio filter
- Renewable bioenergy
More information can be found at http://www.timberstewardship.org.au/
An international trade
Wood packaging, when heat sterilised or fumigated according to the international standard ISPM-15, is safely used for transporting goods all over the world.
TYPES OF WOODEN PACKAGING
Typically wood packaging includes:
- boxes and bins
- crates and cases
- reels, spools & cable drums
Pallets are platforms used to facilitate the handling of goods by forklifts.
Pallets became popular with the advent of the forklift truck and containerised transport as they increased the efficiency of loading and unloading freight.
Today, pallets are used for storage as well as freight and are an integral part of most racking and warehousing systems. In some cases, pallets are even used to display products in retail or wholesale environments.
In Australia, timber pallets are made from both hardwoods and softwoods and they are used in many industries and forms of transport.
Pallets are either owned by the company using them or hired from a pallet hire company. The hired pallets are often referred to as the ‘pool pallets’.
Types of pallets
There are many types of pallet and a range of internationally recognised pallet sizes. [LINK TO Specifications].
Most wooden pallets are of either bearer (called stringer in the USA) or block construction.
Bearer pallets are characterised by the use of two or more (usually three) parallel wooden bearers to form a frame, to which the deck boards are attached.
Block pallets feature perpendicular bearers running at right angles to the parallel bearers. Typically bearer pallets are stronger than block pallets.
Typically, block pallets allow four way entry by forklifts, whereas bearer pallets are usually able to be lifted from two sides.
How many pallets?
Worldwide, there are be billions of pallets in use or in storage. In Australia it is estimated that there are more than 30 million pallets, either in the hire ‘pool’ or privately owned.
The advantages of wooden pallets
The majority, around 85%, of pallets in use are wooden. Reasons for specifying wood as the material of preference include:
- low cost
- good strength and stiffness for the price
- quick and easy to make
- easily customisable
- readily available globally
- made from a renewable material
- high friction to minimise freight movement
- easily repairable
Boxes, bins and crates
Wooden boxes, bins and crates are used in situations that require containment and protection from damage. Often of a large size, timber packaging may be specified with the rigidity and strength required for warehousing and shipping.
A box has minimal internal framing, the side, floor and top panels provide its structural strength and they are usually solid without gaps.
A crate has a frame that forms the structure. A crate may have gaps for ventilation and may be covered with cladding of some form.
A bin will typically have an internal frame for support and more substantial cladding than a crate.
The advantages of wood for boxes, bins and crates are similar to those for pallets, shown above.
Other wooden packaging
Wood is also used in many other packaging applications, ranging from the familiar cable drums and reels to casks, dunnage and wood ‘wool’ (known as excelsior in the USA) made from fine wooden shavings.
Dunnage are pieces of wood used in various ways – such as bearers and spacers – when packing and packaging containers and other transport vehicles.
All wood packaging delivers the renewable, recyclable and environmental advantages of wood while helping to maximise the value extracted from every log processed.
Timber pergolas offer an attractive and economical way to create functional living and entertainment areas in the outdoors. Pergolas designed with care can maximise both winter sunshine and summer shade, ensuring outdoor living is enjoyed all year round. With its natural look, durability and versatility there are few other materials that can match the advantages of timber in pergola construction.
Pergolas are typically constructed via a straightforward post and beam process, which can be attached to an existing building or form a free standing structure. A protective finishing coat will preserve the life of the pergola and a variety of paints and stains are available on the market to facilitate this.
The versatility, strength and natural beauty of timber makes it the ideal material choice for external handrails and balustrades. Usually built from treated softwood and durable hardwoods these timbers can be turned to create a range of styles and designs, resulting in balusters that are unique as they are individual. Painting, staining and oil based finishes broadly cover the wide range of finishing options available and with the appropriate care and attention a timber balustrade can last a lifetime.
This guide provides general information on member sizes, connections and suitable materials to enable the construction of a long lasting, attractive and durable timber handrail or balustrade.
The versatility, beauty and strength of timber makes it the ideal material choice for interior handrails and balustrades. Treated softwood and durable hardwoods are the most popular timber choices and these can be turned to create a range of unique styles and designs to suit a variety of tastes and decors.
When used internally balustrades and handrails are typically finished with a clear lacquer to showcase the natural beauty of the timber and with appropriate care and attention will last a lifetime. Find here general information on member sizes, connections and suitable materials, as well as important considerations, for the specification and construction of interior handrails and balustrades.
The natural appeal, strength and versatility of timber makes it an ideal choice for retaining wall landscaping applications.
Retaining wall systems include cantilevered round or sawn timber, mass wall and crib wall construction. Walls up to one metre in height follow a basic design and can usually be constructed using standard proprietary wall systems. An engineer will be required to plan and design walls greater than one metre, including the footings and drainage.
Drainage of retaining walls is a critical factor in influencing the long term stability of the wall and should thus form a significant part of the design and planning process.
Regular care and maintenance of retaining walls is essential in ensuring the long-term stability and safety of the structure.
All exterior stairs serve a functional purpose, but the choice of timber in the application will turn a functional building element into an aesthetically pleasing feature. And while the construction of stairs is demanding, the investment of time will be returned, with a well constructed timber staircase typically lasting decades.
Exterior stairs are usually built from treated softwood and durable hardwoods and typically finished with paint. The construction procedure described here applies to most general type stairs of either conventional or contemporary construction.
When it comes to stairs there is a multitude of variations available for application depending on the structural requirements of the building. This guide discusses the most commonly specified stair types.
Interior staircase work is considered a specialised area of carpentry and joinery as its construction requires high levels of workmanship, detail and accuracy. Many interior stairs are built from quality joinery timber, cut and seasoned especially for staircases. Interior stairs differ considerably in design, from simple straight flights, commonly used in domestic work, to more elaborate stairs, constructed purposely as stand out features in public and commercial buildings.
The construction procedure described here applies to most general type stairs of either conventional or contemporary construction.