Finger-jointed solid timber (KVH)
KVH, finger-jointed structural timber: production, C24 strength, 15 ± 3% moisture, common cross-sections and lengths, standard and uses.
German: Konstruktionsvollholz
Dried structural timber, graded by strength and appearance. Defective sections are cut out and the pieces are joined with finger joints – toothed, glued joints – producing elements of any length and uniform quality.
How is it made?
The log is split at the pith, and the timber is kiln-dried to 15 ± 3% moisture. Defective sections – for example large knots – are cut out, the pieces are joined with finger joints, and finally the surface is planed and the edges chamfered.
It is available in two qualities: visible (Si) and non-visible (NSi). Visible quality has stricter limits on crack width and a planed surface; dimensional accuracy for both is class 2 of EN 336.
Kiln drying – why does it matter?
KVH is kiln-dried to 15 ± 3% moisture. After installation it no longer dries significantly, so there are far fewer cracks, bending and twisting – the beam keeps its size and shape.
Drying takes place at temperatures above 55 °C for at least 48 hours. The risk of insect damage is therefore negligible: indoors, in dry conditions, no chemical timber protection is needed – according to the German timber protection standard, it is not even permitted without good reason.
Prefabrication: the timber frame is made by CNC
Dimensionally stable, dried timber makes machine joinery possible. The structure is designed in 3D, and the data goes directly to a CNC-controlled joinery machine, which cuts, mills and drills each element individually: angled cuts, traditional carpentry joints such as dovetails, and slots for metal connector plates.
Beams, rafters and studs arrive on site accurate to the millimetre and in sequence, where they only need to be assembled. Wall, floor and roof elements can even be completed entirely in the factory, protected from the weather – which means shorter and more precise assembly on site.
Technical data
- Build-up
- timber split at the pith, dried to 15 ± 3% moisture, defects cut out, finger-jointed
- Raw material
- usually spruce and fir; on request pine, larch or Douglas fir
- Strength
- C24 (bending strength 24 N/mm²)
- Density
- depends on the species – spruce 440–470 kg/m³
- Adhesive
- PUR or MUF, only in the finger joints (approx. 0.5 kg/m³)
- Common sizes
- width 60–140 mm, depth 100–240 mm; stock lengths up to 13 m, longer on request
- Standard
- EN 15497 (finger-jointed), EN 14081-1
- What is it for?
- wall, floor and roof structures, frames
| Width \ depth (mm) | 100 | 120 | 140 | 160 | 180 | 200 | 220 | 240 |
|---|---|---|---|---|---|---|---|---|
| 60 | ● | ● | ● | ● | ● | ● | ● | ● |
| 80 | ● | ● | ● | ● | ● | ● | ||
| 100 | ● | ● | ● | ● | ||||
| 120 | ● | ● | ● | ● | ||||
| 140 | ● |
● available from stock. Stock lengths up to 13 m; other species, visible quality and other strength classes on request.
Applications
- studs of timber frame walls, floor joists, rafters
- visible structures – the requirements cover dimensional and shape stability, cracks and the surface
- additional elements in CLT buildings, for example lintels and timber frame wall sections
What to watch out for
- According to the German timber protection standard (DIN 68800), finger-jointed KVH must not be used where it is exposed to the weather.
- KVH is not produced wider than 140 mm, because thick timber cannot be dried evenly – wider cross-sections need duo/trio beams or glulam.
- For visible structures, order visible (Si) quality.