Requirements of KVH® structural timber

The specification of quality criteria which exceed those required by building regulations were first defined in 1995 in an agreement on KVH® structural timber, and have been continually updated ever since. To minimize cracking and deformation from shrinkage caused by drying, specifications for moisture content and the type of cutting were set down. Other criteria are concerned mainly with the dimensional stability and the appearance of the timber.

Grading criterion

Requirements for KVH®


Exposed areas

Non-exposed areas (KVH®-NSi)

Strength class

C24, C24M

Other strength classes must be agreed upon separately (see table 1.2 of the agreements on construction timber)

Grading class in the case of a visual grading according to DIN 4074-1


Other grading classes must be agreed upon separately (see table 1.2 of the agreements on construction timber)

Product standard

EN 14081-1 for non-finger-jointed KVH® structural timber
EN 15497 for finger-jointed KVH® structural timber


Moisture content

15% ± 3%

Kiln-dried: Wood that was dried to a moisture u of ≤ 20% in a controlled process in a suitable industrial plant at a temperature of T ≥ 55 °C for at least 48 hours.

The specified moisture content is a precondition for dispensing for the most part with preservative treatment, and can also be the precondition for finger joint assembly.

Type of cut

For a log with an ideal growth form, the pith is cut through in two-strand cutting.
Upon request:
Heart plank with d ≥ 40 mm is removed

For a log with an ideal growth form, the pith is cut through in two-strand cutting.




not acceptable

≤ 10% of the smaller cross-section side


Dimensional stability
of the cross-section

EN 336 Dimensional stability class 2:
≤ 10 cm = ± 1 mm; > 10 cm and ≤ 30 cm = ± 1.5 mm

The dimensional stability for the longitudinal dimensions must be agreed between the customer and the supplier.

Knot condition

Loose knots and dead knots not acceptable. Occasional faulty knots or parts of knots up to max. 20 mm in diameter are acceptable.

DIN 4074-1
Grading class S10



S 10: A ≤ 2/5
S 13: A ≤ 1/5
not exceeding 70 mm

The following applies for mechanical grading:
• Knot sizes are not taken into consideration for KVH®-NSi
• A ≤ 2/5 applies to KVH®-Si

Ingrown bark

not acceptable

DIN 4074-1
Grading class S10

Knot bark is added to the knot


Crack width b ≤ 3%
not exceeding 6 mm

Crack width b ≤ 5%

Crack width b relating to the respective cross-section width
Without limitation of the length or the number of cracks
The requirements of building regulations concerning the crack depth must be observed.

Crack depth
- shrinkage cracks
- cracks caused by lightning, ring shakes

Up to 1/2
Not acceptable


Measured according to DIN 4074-1

Pitch pockets

Width b ≤ 5 mm


Corresponds to DIN 68365 quality classes 1 and 2
Without limitation of the location or the number of pitch pockets


not acceptable

Blue stains: acceptable
Shatter-proof brown and red stripes: up to 2/5
Brown rot, white rot: not acceptable

The requirements concerning KVH NSi correspond to those of grade S10 according to DIN 4074-1

Insect attack

not acceptable
(DIN 68365 Quality
 Class 1)       

Insect holes up to 2 mm diameter are acceptable

According to DIN 4074-1


1 mm per 25 mm height

Measured according to DIN 4074-1

Longitudinal warping

≤ 8 mm/2 m with removed heart plank ≤ 4 mm/2m

For split‐heart cut
≤ 8 mm/2 m

Measured according to DIN 4074-1
Meets the requirements for grades S10 and S13 according to DIN 4074-1

Finishing of the ends

Trimmed perpendicular (by agreement)


Surface condition

Planed and chamfered

Levelled and chamfered