Holmen offers a completely customised CLT range. Our custom solutions may be based entirely on CLT or combined with glulam or other construction components, for example.
CLT is a solid wood panel made from planed timber that is glued together, with every other layer rotated 90 degrees for increased dimensional stability. The result is a structural element with high strength and transverse stiffness in relation to its low weight. This creates opportunities for large spans and efficient methods of rapid assembly. The properties of CLT pave the way for a wealth of uses.
Efficient joints and large elements ensure speedy assembly and the material can be worked on using traditional hand tools. With its moisture buffering capabilities, CLT also contributes to a good indoor climate, while the mass timber structure provides good fire resistance.
CLT floor systems can be supplied with large spans, giving plenty of layout options and the choice of large, open spaces. CLT is designed to allow for efficient assembly and can be put to good use in mezzanine or residential floor systems.
CLT walls are usually chosen for their considerable load-bearing and stabilising capacity. CLT also has other good physical properties that benefit any building, such as sound insulation and fire resistance. In addition, the panel’s moisture buffering properties contribute towards a better, more consistent indoor climate.
CLT roof sheathing can be supplied as prefabricated elements that cover a large area and are finished with sheet metal or roof tiles. In this roof structure, the roof is used as a stabilising element, which means that no further stabilising panelling is needed.
CLT is a core part of Martinsons’ offer in halls, apartment blocks and offices.
CLT panels can, in principle, be used for the structural frame in buildings with the same spans and dimensions as concrete. However, the density of CLT is only a fifth of that of concrete and its elastic modulus is more than 10 times lower. This means that sound insulation is around 15 dB less effective for normal thicknesses within the range 100–250 mm.
In offices, for example, where the thresholds are low, it will often be sufficient to cover the CLT with some form of cladding (plasterboard, for example). In apartment blocks, where the acoustic standards are higher, supplementary cladding of some kind is usually required. This might, for example, mean having double walls separating apartments, and a flooring or ceiling layer that complements the CLT floor system. More information can be found in The CLT Handbook from Swedish Wood and in Martinsons’ Brochure for apartment block structural systems.
CLT is regularly used as a framing material even where fire safety requirements are particularly tough, such as for residential buildings over four storeys high. In the event of a fire, the wood material could certainly begin to burn, but the dimensioning takes into account the penetration that occurs and the penetration rate takes into account the charred layer of thermal insulation that forms.
The fire safety class for load-bearing and separating building components, whatever their material, is broken down according to the functions: load-bearing capacity (R), integrity (E, seal against fire gases and flames), and insulating capacity (I, insulation relating to temperature rises on the side not exposed to fire). A time element such as 15, 30, 45, 60 or 90 minutes is then added to fully describe the requirements that a building component must meet. The numbers state the time in minutes that the building component will resist the effects of a standard fire without losing its load-bearing or fire separation function.
A surface material is defined as the visible outer part of a building’s structure that may be exposed in a fire’s early phase, with the surface material class indicating the capacity to prevent or delay flashover and development of smoke.
An untreated CLT panel meets surface material class D-s2,d0.
Where a higher class is required, there are various options, including finishing the CLT with a fireproofing paint or encasing it in a material of a higher surface material classification. Surface material class B-s1,d0 is a relatively common requirement, which is achieved via surface treatment or encasing with another material. Requirements concerning non-combustible finishes can be met using plaster or fireproofing paint.
Apartment blocks of 5–8 storeys are usually classed as Br1 buildings and tend to fall into fire safety class EI60, as well as R90 for a vertical supporting structure and R60 for floor systems. CLT panels in themselves are well able to perform a load-bearing and separating function, but to meet the requirements above and the requirements for surface materials in apartment blocks they are often clad in plasterboard.
Integrity E is met if two glue lines remain intact after a fire. Insulation I is achieved with just a few cm of CLT, which means that all of Holmen’s CLT panels fulfil the requirement.
Swedish Wood has more information on CLT and its fire safety performance.
The examples above are just some of the wide range of permutations that can be used. If you choose to add multiple layers of plasterboard, then slimmer CLT panels can be used. If you wish to use CLT for other fire safety classes or a different kind of sheet cladding, this can be worked out by Martinsons’ structural engineers.