Customised CLT Dimensionally stable, strong and easy to install
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.
Large elements and efficient joints enable rapid assembly, which is good for the overall economics of a project. The material can be worked on using traditional hand tools and makes the fitting of utilities easy. Electricians on site, for example, can drill a hole exactly where they want it.
The low weight makes it simple to achieve efficient assembly with a relatively small crane. Wood is around five times lighter than concrete and therefore places much less of a load on the underlying structure, which is good news where ground conditions don’t permit heavy weights and when adding new floors onto existing buildings.
With its cross-laminated structure, the panel keeps its shape and doesn’t move the way solid timber does due to moisture fluctuations. The structural capacity of CLT is close to that of concrete in terms of material strength, with dimensionally stable and robust elements.
The structure of CLT makes it a dimensionally stable material that offers flexible solutions, with few load-bearing walls and design freedom when it comes to the layout. Spans of 7.4 m can be managed with a completely solid sheet and up to 16 m by reinforcing the cross-section with glulam beams.
The sheets are manufactured as elements of up to 3 x 16 m. CNC machining can be used to form large cutouts or holes in the factory, making work on the construction site considerably easier.
Since CLT requires no drying time, the material can be provided with its final finish immediately after assembly, giving a much better work flow on site and allowing other parts of the construction process to get started sooner.
CLT is made in a quality-assured factory environment, using CNC machining to ensure cutting with incredible precision. This precision saves time and keeps every project on track, without the delays caused by on-site adjustments.
CLT can be ordered in surface finishes from industrial to visible, offering huge scope to create attractive environments as required. The visible grade can also be sanded to achieve great aesthetic solutions. And thanks to its moisture buffering properties, CLT contributes to a good indoor climate at the same time.
The solid CLT panel has extremely good properties when it comes to fire. A 5-layer sheet will usually meet class R60 (residential load) without the use of plaster or other materials.
CLT is produced from renewable raw material and manufactured in an energy-efficient process with minimal environmental impact. The material is a natural part of the ecocycle, as it binds carbon dioxide for its entire lifetime.
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.