Strength classes you won’t find in EN338

Not all strength classes are listed in EN338. Here are the main characteristic properties of some strength classes that appear in machine settings tables for machine controlled grading in Europe.  (The other design properties can be calculated from the equations in EN384). Many of these are not available on the general market, or even in current use in a manufacturing process – but TR26 is a prime example of a commonly traded non-EN338 strength class (at least in the UK market).

Note this previous advice though – in this case, the primary references will be the latest tables of machine settings (known as AGRs or ITTs). These are available most easily from grading machine manufacturers, but can also be obtained through the SG18 group of Notified Bodies.  Everything you will find in EN14081-4 is out of date / replaced by AGRs / ITTs.

Update 8 May 2023: added some new strength classes and extra information 

Strength class	5%ile bending strength (N/mm2)	5%ile tensile strength (N/mm2)	Mean modulus of elasticity (kN/mm2)	5%ile density (kg/m3)	Comments
batten10	10		7	330	A grade for spruce tiling battens from UK and IE
batten12	12		7.5	330	A grade for spruce tiling battens from UK and IE
batten14	14		7.5	330	A grade for spruce tiling battens from UK and IE
C16+	18.5		8	330	A grade for spruce from UK and IE
C25T15	25		11.5	360
C36T22	36.7		13	390
E12	24		12	370	Stiffness grade
E12,5	25		12.5	370	Stiffness grade
E13	30		13	380	Stiffness grade
E14	32		14	400	Stiffness grade
E15	36		15	420	Stiffness grade
E8,5	18		8.5	320	Stiffness grade
ET24		24	18	590	For Eucalyptus globulus
ET28		28	19	600	For Eucalyptus globulus
ET30		30	20	610	For Eucalyptus globulus
ET34		34	21	620	For Eucalyptus globulus
ET38		38	22	630	For Eucalyptus globulus
ET42		42	23	640	For Eucalyptus globulus
L23		13	10	345
L35		21	13	400
L36		22	13	400
L40		26	14	420
L45		27	15	440
LD18		18	12	370	EN1194:1999 Table B.1 (with density)
NapierDA	35		13	460	A grade for Douglas-fir from UK and IE
NapierDB	30		12	460	A grade for Douglas-fir from UK and IE
NapierDC	16		10	400	A grade for Douglas-fir from UK and IE
NapierDD	14		9	400	A grade for Douglas-fir from UK and IE
NapierLA	30		13	480	A grade for larch from UK and IE
NapierLB	28		12	440	A grade for larch from UK and IE
NapierLC	21		9	400	A grade for larch from UK and IE
NapierLD	20		8	390	A grade for larch from UK and IE
NapierSA	25		11	375	A grade for spruce from UK and IE
NapierSB	22		10	360	A grade for spruce from UK and IE
NapierSC	16		8	320	A grade for spruce from UK and IE
NapierSD	15		7	310	A grade for spruce from UK and IE
TR26	28.3		11	370	A grade for trussed rafters in the UK
uC12	12		6	290	A grade for loblolly and slash pine from Uruguay or Brazil

There are also some old tension strength classes with no characteristic density (only “informative values”). These are based on EN1194:1999 Table B.1. Since they are no longer in use, the settings tables with these grades are being withdrawn. These classes are LS11, LS13, LS15, LS18, LS22, LS26. These map on to LD11, LD15, LD18, LD22, LD26 (these is no LD13), which in turn map on to the EN338 T classes (with the exception of LD18, which has slight mismatch of density).

Many old tension strength classes match with EN338 T classes

L16 Match for T10
L17 Match for T11
LD11 Match for T11
LT11 Match for T11
L22 Match for T13
L24 Match for T14
L25 Match for T14,5
LD15 Match for T14,5
LT14 Match for T14,5
L27 Match for T16
L30 Match for T18
LT18 Match for T18
LT21 Match for T21
LD22 Match for T22
LT22 Match for T22
LT24 Match for T24
LD26 Match for T26
LT26 Match for T26