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This the most common strength class of Softwood available in the UK. It is ideally suited to most general structural applications, such as studs, joists, rafters and other cut roof or framing applications.

The strength properties for C16 are given below:

 

C16 C24
Strength properties in N/mm2
Bending 16 24
Tension parallel 8.5 14.5
Tension perpendicular 0.4 0.4
Compression parallel 17 21
Compression perpendicular 2.2 2.5
Shear 3.2 4.0
Stiffness properties in kN/mm2
Mean modulus of elasticity parallel bending 8 11
5 percentile modulus of elasticity parallel bending 5.4 7.4
Mean modulus of elasticity perpend

icular

0.27 0.37
Mean shear modulus 0.50 0.69
Density in kg/m3
5 percentile c density 310 350
Mean density 370 420

For more information see the resources sections

This is the second most common strength class of Softwood available in the UK. Its strength properties are greater than C16 which is usually reflected in its higher cost. It is ideal where longer clear spans are required, or greater roof loads are likely to be imposed. 

The strength properties for C24 are given below 

For more information see the resources sections

Extract from BS EN 338 Table 1

Strength classes for softwood based on edgewise bending – strength, stiffness and density values

C16

C24

Strength properties in N/mm2

Bending

16

24

Tension parallel

8.5

14.5

Tension perpendicular

0.4

0.4

Compression parallel

17

21

Compression perpendicular

2.2

2.5

Shear

3.2

4.0

Stiffness properties in kN/mm2

Mean modulus of elasticity parallel bending

8

11

5 percentile modulus of elasticity parallel bending

5.4

7.4

Mean modulus of elasticity perpendicular

0.27

0.37

Mean shear modulus

0.50

0.69

Density in kg/m3

5 percentile c density

310

350

Mean density

370

420

This grade for structural softwood has been specifically developed for the manufacture of Trussed Rafters. The grades characteristic properties can be found in the TRA leaflet included in the resources section of this website.

This is one of the most common strength classes for Hardwood available in the UK. It can be achieved by a variety of Hardwood species such as those listed below and is ideal in high strength applications such as beams or feature trusses.

BS 5756 Visual Grade Species Origin
HS Keruing South East Asia
HS Karri Western Australia
HS Opepe West Africa,
HS Balau/Bangkirai South East Asia
TH1 American white oak USA

 

D50
Strength properties in N/mm2
Bending 50
Tension parallel 30
Tension perpendicular 0.6
Compression parallel 30
Compression perpendicular 6.2
Shear 4.5
Stiffness properties in kN/mm2
Mean modulus of elasticity parallel bending 14
5 percentile modulus of elasticity parallel bending 11.8
Mean modulus of elasticity perpendicular 0.93
Mean shear modulus 0.88
Density in kg/m3
5 percentile c density 620
Mean density 740