Timberpride is a cut above the rest when it comes to Structural Grading, as we have our own in-house TRADA Grader (TRADA meaning Timber Research and Development Association – Fancy, right?!)
Read on to find out why this is important and how it can help you.
Strictly speaking, every piece of timber supplied for a structural application must have a CE certificate of conformity so that the finished building can gain building regulations approval. Many people rely on their buildings inspector to give them this compliance, but this can be a headache if the structure is complete and the inspector fails a timber.
This is where a timber merchant with an in-house grader can save lots of trouble.
Timberpride has a BM TRADA trained and certified hardwood grader and has a regular programme of quality/accuracy audits to allow us to issue CE compliance certification with structural orders.
Structural hardwoods are visually graded as every piece is unique, in contrast, softwoods are often stress graded (tested for destruction to find maximum strength) as it is much easier to produce near homogenous softwoods.
Visual hardwood grading primarily concerns itself with the size of knots as a proportion of each face width, a slope of grain, splits and wane. This is why it is difficult and expensive to achieve a TH1 grade as a maximum permissible knot size on a narrow face may be unachievable from a beam grade log.
Taking all these factors these into account a beam can be given a visual structural grade of THa and THb for section sizes over 20000mm2 and TH1 and TH2 for section sizes below 20,000mm2. These visual grades then have a structural grade attached, THa and TH1 are D40, whilst THb and TH2 are D30. Although an individual piece of Oak may be capable of achieving the strength required to qualify as a D70, D30 and D40 are the only grades that can legally be applied to an oak beam. This is because hardwoods are graded to give assurance of the minimum strength the piece can achieve, it does not tell how strong a piece is.
Structural engineers and architects can now use their tables to calculate the required section sizes for a given span and loading, obviously, a D30 beam will need to be larger in section to give the same strength as a D40 one performing the same task.
But remember, visual grading only concerns itself with the appearance of the beam now, not how it will look in the future. It may be obvious that the sap will rot off a beam in time, but it does not reduce its strength now. The sap is allowed in D40 and D30 as it is no weaker than the heartwood, if you want sap free timber you must specify it, simply listing D40 does not mean you have requested sap free.
If a TRADA Grader is something you need, call now!