Timber Grading Explained
Last Updated Sep 2, 2013 · Written by Rob Schneider
Timber grading systems have been developed to ensure quality control in the industry and help consumers buy the right timber for their needs. The only problem with the grading systems is that the only ones who really understand them are those who work in the industry. What's the difference between an S1 and an F14 length of construction softwood or hardwood? Is Standard grade timber flooring inferior to Select grade?
We use timber for a variety of purposes. The timber we use for building a house doesn't have to look pretty, but it does have to be strong. The timber we use for flooring or furniture making must be strong enough to bear a load and aesthetically pleasing as well. Timber grading tests and standards take both strength and appearance into consideration.
Structural Timber Grading
Structural timber undergoes two different types of stress tests to determine its strength and rigidity:
- Visual stress grading is undertaken to determine the inherent strength of the timber as determined by its species and the quality of a specific parcel of timber as determined by the defects in selected lengths of timber. Unseasoned timbers are graded S1 through S7 and seasoned timbers are graded SD1 through SD8. In both cases, the lower the number, the higher the strength of the timber.
- Mechanical stress testing is performed to determine the rigidity or strength of timber. Mechanical timber grading is highly technical, but for practical purposes, the main thing you need to know is that in this case, the higher the number, the stronger the timber. The mechanical grading system grades timbers regardless of species from F1 (very weak) to F34 (extremely dense). For example, radiata pine is often graded between F5 and F14, while tallowwood, an extremely dense hardwood, is usually graded between F17 and F34.
Aesthetic Timber Grading
If you are out selecting timber for a hardwood floor, it will have been stress graded before it has been deemed acceptable for sale as flooring. All you need to think about is how it is going to look after it has been laid and polished. There are three grades or categories of flooring to choose from:
- Select grade has a minimum number of knots, sap streaks and other characteristics. It is straight grained and uniform in appearance.
- Standard grade has a varied appearance, with knots, sap streaks, burls and other distinctive characteristics.
- Character grade can best be described as rustic in appearance.
These grades do not say anything about the quality or durability of the timber. They are meant to be a guide to the aesthetic suitability of a timber. Select grade timbers are ideal for modern, minimalistic interiors while character grade may be perfect for a mountain top chalet.
Whether you are buying timber for construction purposes or for a home improvement project, you are the final timber grading "specialist." Only a portion of the timber in any pack of timber has been exhaustively graded, so expect to find a few pieces in any pack that will have unusable defects. The combination of the timber grading system and your final inspection will ensure that the timber you use will be equal to the purpose you use it for.
Image courtesy of Ironwood.