KVH is kiln-dried solid structural timber, optionally finger-jointed along its length. BSH (glulam) is made from timber laminations bonded together to build the beam's cross-section. Both can be used in appropriately designed structures. The choice depends on span, loads, dimensions, appearance and exposure to moisture.
Choosing timber for a pergola or canopy means understanding more than the beam dimensions. KVH and BSH describe timber products; C24 describes a strength class. Appearance quality and suitability for outdoor exposure are separate considerations.
What is KVH timber?
KVH stands for Konstruktionsvollholz: solid structural timber that is kiln-dried and strength-graded, with controlled product properties. It is usually made from softwoods such as spruce or pine. Binderholz: KVH.
It may be supplied as an unjointed piece or finger-jointed along its length. Factory finger joints are part of the manufacturing process. KVH product definition.
Its benefits include controlled moisture, dimensional accuracy and a basis for structural design. Drying and sawing requirements help reduce subsequent shrinkage, distortion and cracking compared with wet, freshly sawn timber. The specified delivery moisture content is 15% ± 3%. KVH requirements.
What is BSH timber?
BSH stands for Brettschichtholz, or glued laminated timber (glulam). Dried, graded timber lamellas are bonded together with their grain running lengthwise. Unlike lengthwise finger-jointing alone, this builds up the beam's cross-section.
Benefits include dimensional stability, large available sections and a variety of shapes. These make it useful when designing larger spans or special structures. Binderholz: glulam.
KVH versus BSH
| Feature | KVH | BSH |
|---|---|---|
| Construction | Solid timber, optionally finger-jointed lengthwise | Laminations bonded to build the section |
| Strength marking | Often C24 | For example GL24h, GL24c or GL28c |
| Project selection | Posts, rafters and beams when appropriately sized | Useful for larger sections or special shapes |
| Appearance | Natural grain, knots and possible finger joints | Visible lamination lines and natural timber features |
BSH is not automatically twice as strong as KVH. Compare actual grades, dimensions, span and loads. KVH properties; glulam technical data.
Visible and concealed quality: Si and NSi
KVH specifications may distinguish Si (visible use) and NSi (concealed use). Visible quality has higher aesthetic requirements; concealed quality permits more appearance variations. Agree the supplier's actual specification before ordering.
Both can have the same C24 strength class. A smoother surface does not itself increase load capacity, and visible quality does not mean completely knot-free or crack-free timber. KVH surface-quality guidance.
Glulam is also offered in visible and industrial appearance qualities. Glulam appearance grades.
Visible quality is not an outdoor exposure rating
A beam can remain visible inside a dry room or be exposed to rain in an open pergola. Check the particular product's suitability and protection requirements for the expected moisture conditions. Si, NSi and C24 do not themselves certify resistance to rain or decay. Timber service conditions; glulam service conditions.
What does C24 mean?
C24 is a strength class under EN 338, not an appearance grade. The number refers to characteristic bending strength of 24 N/mm², not a universal beam capacity in kilograms. Glulam uses grades such as GL24h and GL28c. KVH strength properties; glulam grades.
Are cracks normal?
Some drying cracks are permissible without making the timber unsuitable. Timber responds to moisture changes. Permissible cracks are accounted for in grading and design, but C24 does not make every crack harmless. Type, depth and position matter; surface width alone is insufficient. KVH guidance on drying cracks.
Ask the supplier or a structural engineer to assess deep, growing or connection-area cracks and suspected glulam delamination. A photograph may not reveal depth.
Choosing timber for your pergola
Start with the intended use, dimensions, column spacing, location and roof covering. Agree appearance quality for exposed beams and check actual timber dimensions against your metal connectors.
Planning a pergola or canopy? Send LuxShade your dimensions, location and roof idea to discuss the configuration and connectors. Contact us on WhatsApp.
Frequently asked questions
Is KVH the same as C24?
No. KVH describes a timber product; C24 is a strength class. Ask for both the product specification and the declared strength grade.
Is BSH always stronger than KVH?
No universal comparison is possible. Compare the actual grades and beam dimensions for the same span and loading.
Can visible and concealed timber both be C24?
Yes. Appearance requirements and strength grading are separate. Visible quality is not an outdoor durability rating.
Does a crack mean the beam is defective?
Not necessarily. Some drying cracks are permissible, but deep or growing cracks, damage near connections and suspected delamination need assessment.
Related pergola guides
Building a wooden pergola with metal connectors · Concrete foundations for a pergola