British frame grade

Requirements on the birch square edge timber


Moisture content: 14 % (+/- 2%)

Cross section: 

Thickness: 24 мм

Width: 24; 35; 35; 70; 95; 120; 145 мм

Length: 1,0; 1,8; 2,1; 2,4; 2,7; 3,0; 3,3; 3,6; 3,9 м

Maximum deviation of dimensions and shape:

for length:  +5 / +10 мм,

for width:  - 0,5/ +0,5 мм,

for thickness: - 0,5/ +0,5 мм

The material shall be trimmed on both ends. The bow shall not exceed 10 mm.

Surface finish:  S4S or S2S. Optionally the side edges can be left rough after sawing in four side planer/moulder. 

Quality of the lumber


- any amount of sound, intergrown or partially intergrown knots and knots with fine cracks.

- any amount of black and split knots, but not exceeding 2/3 of the board’s width

- false heartwood, wormholes and other flaws, not affecting mechanical strength of the wood. The boards with false heartwood on both sides shall not exceed 20% of the total batch volume. 70% of the boards are allowed to have false heartwood on one face.

- cracks on the ends not exceeding 15 mm on both sides.

- minor wane (not exceeding 8 mm)

Not permissible:

Hit or miss, saw damage, any kind of decay, heartwood, mould, rotten, tobacco and loose knots as well as the knots,  laying across the whole width of the face; face shakes, wane, exceeding the specified size, mechanical damage more than 1 mm in depth.