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^®		Notes
Grading criterion	Exposed areas (KVH^®-Si)	Non-exposed areas (KVH^®-NSi)	Notes
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	S10		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.
Wane	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
Knots	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
Cracks	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
Discoloration	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
Twisting	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

New KVH® series of transparencies entitled “Hochleistungsbaustoffe für den Holzbau” (“High-performance building materials for timber construction purposes”)