Structural Timber and Ratings
Barwon Timber stocks a large range of structural timbers. Different species of timber have different structural ratings. This can depend on the species and also if the material is green or kiln dried.
Most pine is machine grade, but most other timber is F rated. The difference in structural grading is outlined below.
MGP stands for machine graded pine, and is a system used for particular pines, especially radiata, slash and Caribbean. Instead of being based on the bending strength of the piece, MGP is a measure of its modulus of elasticity (MOE), which takes into account other properties, such as stiffness, compressive strength and shear strength.
The higher the MOE of a piece, the stiffer it is. When this is measured by an MGP machine stress grader, the board is given a grade which is simply an abbreviation of the MOE category that it falls into.
That is:
MGP 10 has an MOE of 10,000 megapascals (MPa)
MGP 12 has an MOE of 12,700 Mpa
MGP 15 has an MOE of 15,200 Mpa
Using MGP in place of F Graded Timber
It’s important to note that although MGP material may be substituted for F graded material, F graded material must not be used where MGP material has been specified.
This is because the MGP grades have design tables for a range of properties, whereas F grades are based on bending strength only. So it is possible that the architect or builder who has specified an MGP grade for a structural member is relying on design characteristics such as compressive strength or shear strength, which would not be accounted for in an F graded piece.
Below are the three main MGP grades and the F grades they can replace.
MGP 10 can replace F5
MGP 12 can replace F8
MGP 15 can replace F11
An F grade is a measure of the bending strength of a piece of timber. ‘F’ stands for force in megapascals (MPa) and is the amount of force a piece of timber can withstand without bending beyond an acceptable limit. A piece graded to F11, for example, will have a safe working stress in bending of 11 MPa.
Here are the colour codes used for the most common softwood F grades.
– F4: Red
– F5: Black
– F7: Blue
– F8: Green
– F11: Purple
Mechanical stress grading is used to measure the tension in a piece of timber, and it’s measured by how much force will be needed for that specific task. The timber is graded based on its own measurements with an F or MGP system.
Of the many tree species in this world, there are more than 30,000 species with various properties that make them valuable for different purposes.
It is inevitable that there will be a large range of properties within each species and some overlap between the groups. If you need more information about a species of timber, for a specific grade please contact our timber team.
