Requirements of KVH® structural timber

split-heart cutting
heart-free cutting

The specification of quality criteria which exceed those required by building regulations first came in 1995 with an agreement on KVH® structural timber, and these 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 to be met by KVH®

Remarks

Exposed areas
(KVH®-Si)

Non-exposed areas (KVH®-NSi)

Grading class compliant
with DIN 4074-1

Min. S10TS;
C24 in accordance with DIN 1052

The decisive strength and stiffness properties are given in DIN 1052.

Moisture content

15% ± 3%

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 cutting

Split-heart,
free-of-heart on request

Split-heart

Split-heart:
Given that the pith does not always automatically run through the middle of the log, split-heart is defined as follows: For a log with an ideal growth form, the pith would be cut through in two-strand cutting.

Free-of-heart: Heart plank with d ≥ 40 mm is removed

Wane

Not permitted

Measured at an angle
≤ 10% of the smaller
cross-section side

 

Dimensional stability
of the cross-section

DIN EN 336 Dimensional stability class 2:
                w ≤ 100 mm:             ± 1 mm
                w > 100 mm:             ± 1,5 mm

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

Knot condition

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

DIN 4074-1
Grading class S10

Replacement with natural wood dowels is permitted.
Maximum of 2 adjacent to each other permitted for Si.

Knot diameter ratio

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

Knot diameter ratio A is determined in accordance with DIN 4074-1.
The following applies for mechanical grading:
• Knot sizes are not taken into consideration for KVH®-NSi
• A ≤ 2/5 applies for KVH® -Si

Ingrown bark

Not permitted

DIN 4074-1

 

Cracks, radial cracks caused by shrinking (shrinkage shakes)

Width of the crack w must be ≤ 3% dof the respective cross-section width

DIN 4074-1

For Si the requirements are higher than those applicable to grading class S10
in accordance with DIN 4074-1.

Pitch pockets

Width ≤ 5 mm

-

Additional criterion

Discoloration

Not permitted

DIN 4074-1

For Si the requirements are higher than those applicable to grading class S10 in accordance with DIN 4074-1

Insect attack

Not permitted

DIN 4074-1

For Si the requirements are higher than those applicable to grading class S10 in accordance with DIN 4074-1

Twisting

-

-

The permissible extent of twisting is not specified in further detail because no unacceptable twisting is to be expected if all the other criteria are complied with.

Longitudinal warping

for split-heart cutting ≤ 8 mm/2 m
for heart-free cutting
≤ 4 mm/2 m

for split-heart cutting ≤ 8 mm/2 m

In comparison:
In accordance with DIN 4074-1 S10 und S13:
≤ 8 mm/2 m

Finishing of the ends

Trimmed perpendicular

 

Surface quality

Planed and chamfered

Leveled and chamfered

 

Finger-jointing

DIN EN 385