Graded Timber – What Is Graded Timber?
Graded Timber is the most versatile hardwood available in today’s timber yard. It can be used for flooring, decking, siding, paneling, facades, moldings and more. It is also the most cost effective wood available. A great variety of styles and stains are available, which can give you many opportunities for design.
Uprated Timber is typically sold as a dry, seasoned, split-off piece. It has a very coarse texture with a coarse wavy to straight grain and size can range from +/ 4mm to 5.5mm at the edge, with some visible waying and twists. There is no minimum joint angle requirement for this graded timber
Carcass or strip timber has been cut into blocks of equal height, width and depth for maximum stability and sturdiness. This grade of graded timber displays straight grain with medium to fine visible knots. The timber has a straight grain and is highly resistant to splitting and cracking. It has a good visual grading with fine striation patterns that are good for exterior applications and straight grain.
The term’seasoned timber’ refers to any piece that has been thoroughly seasoned by kiln drying. Kiln drying of unseasoned timber enables it to retain its quality characteristics over time. Storing unseasoned timber in a moisture free environment helps retain its quality characteristics and prolongs its durability. When storing timber used for end use, it is important to note the storage conditions. Before purchasing it, inspect the piece for moisture content and ensure that it is under no moisture stress for extended storage.
The softwoods include soft red, white, pink, orange, yellow and brown hard woods. Hard woods have straighter grain, higher density and straight grain. Softwoods can be classified as perfter, sloping grain, flat-grain, and scalloped-grain. Kiln dried softwoods have a very straight grained appearance with medium soft to medium visible knots.
Graded Timber is graded on the basis of the number of unique features that distinguish one from the other. Some characteristics that differentiate one type of wood from another are color, texture, pattern, sapwood color, shape, and structure. Colors range from light to dark brown depending upon the different species of wood and maturity. The texture may be soft to rough and the pattern and structure ranges from fine to coarse.
Kiln dried hardwood cedar deck boards and split bamboo planks are graded on the basis of the number of knots per inch. Knots are counted in the order that they appear in the grain, i.e., first at the edge, then towards the center, then crosswise to the next edge, etc. The grades are usually based on the appearance of the grain at different distances from the center of the plank. Decking products like hardwood decking and floating cedar planks differ in grades due to these differences in the knots per inch.
Grading is based on the assumption that the timber possesses a series of positive and negative stresses that may affect its strength or weakness. Straining occurs when the board’s grains are pulled by the tension. This leads to planks that are bow shaped or distorted. The difference in the structural properties of the face and cross section is termed as stress grading.
Graded timber products are manufactured to meet the exact visual requirements of end-builders and construction professionals. In spite of this, it is seen that most builders prefer to work with pre-finished wooden structures. Pre-finished timber has undergone the process of visual stress-grading. The concept of visual stress-grading is quite a simple one.
Visual grading involves various processes including cross-grain sorting, lamination and perforation. Cross-grain sorting starts from the grain direction while perforation is done after the timber cross-grain. The main objective of lamination is to add additional strength to a board by preventing buckling due to external pressure. Australian standard denotes the minimum stresses allowed to be applied to timber. The required strength for a given weight and cross-grain arrangement of the boards are calculated.
Strength grades in a structural timber grading system include:
The visual grading criteria are used to assess the characteristics of a timber after it has been cut. After the timber has been cut, an unqualified and trained person checks the surface and the internal and external properties of the timber. The person then checks for variations in the board based on the required properties of the structure.
There are three main types of grading systems: i) Full F Grade, ii) IGR or Initial Green Grading, and iii) Supplemental Silver Grading System. The first two are categorized according to the direction of change in the board’s natural color. The silver-grade has been recognized as the ideal type of grading for resisting both heat and moisture. It is important for structural analysis and planning purposes.
To assess the strength and standardization of the board, several measurements are taken to evaluate these characteristics. Generally, the machine grading and the manually graded boards have similar characteristics and the only difference is their values. The machine grading is characterized by a number of measurements in order to evaluate the characteristics of the board.
In addition, to make the grain and the appearance consistent and smooth, there are several load bearing design features that are used in order to increase strength. For instance, the flat grain, which is found in softerwoods such as pine, elm, Douglas fir and spruce; and the straight grain, which can be seen on hardwoods such as oak, hickory, maple and beech. In order to allow the boards to carry loads efficiently, the structure must meet the load bearing design guidelines prolific ghostwriting.