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Oak Beam Grading Service

Posted in Railway Sleeper News by Admin on March 14th 2014

We employ BM TRADA certified graders on site who are able to grade freshly sawn oak beams to THA (D40), THB (D30), TH1 (D30), or TH2 (D24) strength grades.

THA grading will cost an additional 20% of the price of QP1, and THB grading will cost an additional 10% of the price of QP1. Please use our oak beam cost calculator for pricing.

Explanations of our three most popular grades are given below.

QP1 Grade (First Grade)

All our structural oak beams are graded to QP1 as standard.

QP1 grade beams have a minimum of 3 straight edges with tolerance of a small amount of wane to one edge (with slight tolerance of wane on two edges maximum if the minimum width exceeds 90% of the width of the piece.). Slight traces of heart tolerated on two faces. Enclosed heart permitted. Sound knots are acceptable, as long as their diameter does not exceed one half of the width of the face or edge. Two sound dead knots are permitted per linear metre as long as their individual diameter does not exceed one quarter of the width of the face or edge. On 10% of the pieces of the batch black streaks, brown rot, curly grain, bark pockets can be present. Some black bore holes can be accepted. Heart shakes, ring shakes and frost cracks are permitted on the ends of the pieces, as long as they do not appear on the faces. Face shakes tolerated.

They will have no insect damage (with the exception of pinholes left by ambrosia beetle), no active infestation of insects, or other detrimental characteristics. QP1 ticks every box for the construction industry and sympathetic period property restorers.

THA Grade (D40 Strength Class)

This is the UK equivalent to QPA grade.

Knots - Not greater than 0.2 of the thickness or width to which it relates.
Longitundinal Separation Of Knots - Knots accumulative if longitudinal separation is less than twice the width or 300mm (whichever is lesser), or when the grain has not fully recovered.
Slope Of Grain - Not greater than 1 in 12. Within 500mm of ends not greater than 1 in 6.
Fissures (Through The Thickness) - Only permitted at ends with length not greater than the width of the piece.
Fissures (Not Through The Thickness) - Not greater than 1m or a quarter of the length of the piece.
Wane - Full edge and face dimensions may be reduced by up to one third of the dimensions of the piece. Length of wane is unlimited.
Distortion (Bow) - Not greater than 10mm over a length of 2m.
Distortion (Spring) - Not greater than 8mm over a length of 2m.
Distortion (Twist) - Not greater than 1mm per 25mm width over a length of 2m.
Cup - Unlimited.
Bark Pockets - Within 500mm of the ends, not greater than the width of the piece. Elsewhere not greater than 1.5 times the width or 0.2 times the length of the piece, whichever is the lesser.
Biological Damage And Other Defects - Worm holes and pin holes are permitted providing they conform to the requirements in 4.8 of BS 5756: 2007. No active infestation is permitted. No decay is permitted other than in unsound knots. Stain free from decay is permitted.

The length of fissures and the amount of distortion are linked with moisture content, therefore, the limits given can only be applicable at the time of grading.

THB Grade (D30 Strength Class)

Knots - Not greater than 0.75 of the thickness or width to which it relates.
Longitundinal Separation Of Knots - Knots accumulative if longitudinal separation is less than twice the width or 300mm (whichever is lesser), or when the grain has not fully recovered.
Slope Of Grain - Not greater than 1 in 4.
Fissures (Through The Thickness) - Only permitted at ends with length not greater than the width of the piece.
Fissures (Not Through The Thickness) - Not greater than 1m or a quarter of the length of the piece.
Wane - Full edge and face dimensions may be reduced by up to one third of the dimensions of the piece. Length of wane is unlimited.
Distortion (Bow) - Not greater than 10mm over a length of 2m.
Distortion (Spring) - Not greater than 8mm over a length of 2m.
Distortion (Twist) - Not greater than 1mm per 25mm width over a length of 2m.
Cup - Unlimited.
Bark Pockets - Within 500mm of the ends, not greater than the width of the piece. Elsewhere not greater than 1.5 times the width or 0.2 times the length of the piece, whichever is the lesser.
Biological Damage And Other Defects - Worm holes and pin holes are permitted providing they conform to the requirements in 4.8 of BS 5756: 2007. No active infestation is permitted. No decay is permitted other than in unsound knots. Stain free from decay is permitted.

The length of fissures and the amount of distortion are linked with moisture content, therefore, the limits given can only be applicable at the time of grading.

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1 Comment
sebastien April 7th 2015 11:13:20 PM
which grade are the Air Dried beams? Is it possible to order them with the same grading as green oak and with the same price differential (20% and 10%)?
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