Published: 30/10/23 By: Mike Bekin
Grading systems are used to tell us (and you!) quickly more about the timber quality we are supplying. When it comes to Oak sawn timber, we use two grading categories – appearance (also known as visual) grading and mechanical strength grading – to get a good idea of what to expect from each plank or beam that comes our way. But what do these systems actually tell us about the the wood? Let us take a look at the visual aspect of grading.
Appearance Grading Oak Sawn Timber
As the name suggests, appearance grading refers to an expert looking at the visual properties of the Oak to learn more about its characteristics and suitability for different applications. In the UK, timber is graded to European standard EN 975-1, and is largely used for carpentry, joinery and other applications where appearance is important. For more info and images, please click here
When looking at how timber is graded, you will see a series of letters. For Oak, it might look something like this:
QSA
Q – The first letter of the Latin name of the timber. For Oak, the Latin name is Quercus so the first letter is Q.
S – To signify what the Oak product is. S: selected boards; B: boules; F: strips and square-edged timber; P: beams.
A – To tell us more about the quality grade. A is exceptional quality and then 1, 2, 3, and 4 are used to indicate quality in decreasing order, where 1 is good and 4 is poor.
Sometimes an X is also used at the end of the three letters to signify sapwood on one of the faces, and XX indicates sapwood on both faces.
Dimensional Grading of Oak Timber Boules
When dimensional grading, Oak is split into product categories.
Boules are categorised by dimensions according to the width at the midpoint of the central board. Grade QBA has a width of or less than 350mm. Grades QB1-QB4 have a width of or less than 250mm.
Appearance Grading Rules
When looking into how to grade Oak, any size variations are not considered. For selected boards, each board is judged based on quality and no higher than 10% of the boards with a lower grade than that specified are allowed.
When it comes to boules, each is looked over and if any characteristics which do not follow the grade definition are found, the volume is adjusted. Permissible grade proportion is:
≥ 65% Specified grade
< 25% One grade lower
< 10% Two grades lower
When it comes to strips and square-edged timber, the quality of every piece is judged based on the appearance of its surfaces and, if needed, its edges. This assessment considers the presence, amount, location and dispersion of any characteristics and features such as knots, as well as specific cutting patterns and any resulting impairments.
For beams, only aesthetic features which appear across the entirety of the timber are considered. The only exception to this rule is dead knots.
Rules For Selected Boards
- Consider attributes on the upper surface of the timber, defined as the side visible on the production line post-sawing.
- If specific measurement arrangements are in place, determine quality based on the surface being measured for width.
Rules For Boules
- Account for attributes on the upper surface of the stack forming the boule.
Rules For Strips and Square-Edged Timber
Grading Surface:
- Consider attributes on the highest quality surface of the timber.
Knots:
When it comes to knots, graders will factor in the timber’s length or look at the most affected area of the wood. Except for Q-F 1a, the concept of equivalence permits any distribution of knots under the conditions that:
- The diameter of each knot is smaller than the authorised diameter.
- The total sum of diameters remains below the maximum permitted value.
Example for Q-F 2:
- Maximum allowed knot diameter: 25 mm.
- Maximum count: three, totalling 75 mm (25 mm x 3).
Rules For Beams
When grading beams, the entire beam will be considered and features which are present across the full length (apart from dead knots) will be noted.
Grading Boules and Boards
When looking at boules and boards, grading categories are defined by the following considerations:
Grades QBA and QSA:
- Straight boards with a straight grain (slight imperfections are allowed)
- One knot with a diameter of no more than 20mm
- A single sound knot which takes up less than 15% of the width of the board
Grades QB1 and QS1:
- Less than 8 knots no bigger than 5mm
- Sound knots no larger than 25mm in diameter
Grades QB2 and QS2
- Sound knots no larger than 40mm
- Multiple knots less than 5mm in diameter
Grades QB3 and QS3
- Sound knots no bigger than 10mm
- Or sound knots up to 70mm when equivalent to a single knot less than 160mm
Grading Strips and Square-Edged Timber
When looking at grading strips and square-edged timber, the following applies:
Grades QF1a:
- Straight grain with no features apart from sound knots
- Sound knot which is smaller than 10mm
- 20% of all boards can have an extra sound knot
Grades QF1b:
- Almost no features apart from sound knots
- Sound knots which are smaller than 5mm disregarded
- Up to 3 knots no bigger than 12mm
Grades QF2:
- Almost no features apart from knots
- Sound knots which are smaller than 5mm disregarded
- Up to 3 knots no bigger than 25mm
Grades QF3:
- Sound knots which are smaller than 10mm disregarded
- Up to 3 knots no bigger than 40mm
- A dead or unsound knot smaller than 20mm
- Wane less than 3mm
Grades QF4:
- Sound knots which are smaller than 70mm allowed
- Two dead or unsound knots allowed, one smaller than 20mm and one smaller than 35mm
- Wane less than 10% of the width of the timber and 20% of the length
Grading Beams
When grading beams, the following are taken into account to categorise the timber:
Appearance grade QPA:
- Sawn timber with sharp arrises in beams less than 3m
- Wane less than 10% of the width and less than 25% of the length
- Sound sapwood is allowed on two arrises as long as the width is less than 15% of the total face width
- Intergrown sound knots no more than ? the width of the face
- 2 dead knots less than 15mm in diameter per metre
- Slight traces of heartwood and boxed heart permitted
Appearance grade QP1:
- Sawn timber with sharp arrises
- Wane less than 10% of the width and less than 30% of the length
- Sound sapwood is allowed on two arrises as long as the width is less than 15% of the total face width
- Intergrown sound knots no more than half the width of the face
- 2 dead knots less than ¼ of the face width
- Traces of heartwood and boxed heart permitted
- Brown streaks, brown pith and black holes are allowed on a few of the beams
Appearance grade QP2:
- Wane less than 15% of the width and less than 30% of the length
- Unsound knot no more than 15% the width of the face
- All dead knots allowed as long as no more than ? of the face
- Traces of heartwood and boxed heart permitted
- Sound sapwood, sound knots, sloping grain, brown streaks, brown pith and black holes are allowed
Find High-Quality FSC-Certified Oak at EcoChoice
At EcoChoice, we pride ourselves on the quality of our sustainably sourced timber, including our Oak. With all our wood graded to UK standards, we know that we are delivering the best timber for your needs. To learn more about our services or begin an order for premium quality Oak today, get in touch with our team.
Image: Gorloff-KV / Shutterstock.com
