Cross-laminated (Crosslam or CLT) timber - Introduction

A cross-laminated timber panel (aka 'Crosslam' or 'Xlam') is a method of construction that uses timber to form load-bearing solid timber wall, floor and roof panels. Structural openings, such as doors and windows, are incorporated within the panels. In many cases only insulation and cladding is added to the external face to achieve high standards of thermal performance.

The methodology of layering, stacking and fastening softwood boards to create panels is what differentiates the members of the SWP family. The more common cross-laminated panels are characterised by placing and gluing boards across each other in layers; Another, visually distinctive, technique is to assemble a solid panel through gluing or dowelling together a series of timber ‘posts’. 

Panels are commonly fabricated up to around 4m in width and 15m in height, according to technique and manufacturer. The panels can be assembled to create most types of building including housing, which at Murray Grove in London reaches a record nine storeys.

The traditional key advantages of prefabricated components are speed, efficiency and precise tolerances. SWPs tick-off these features and combine them with attractive environmental and energy-efficient attributes such as use of a renewable resource, carbon sequestration, low waste, relatively low embodied energy and an inherent high standard of airtightness.

 

Some Pros & Cons of crosslam construction

Pro Can replace structural concrete, masonry or steel
Pro Timber is renewable and sequesters carbon during growth
Pro Construction time is very fast - services can be installed and finishes applied whilst panel installation continues.
Pro Higher tolerances achievable through prefabrication
Pro Relatively light weight of panels allows reduction in the size of the foundations compared with traditional construction. Reduced concrete equates to reduced embodied energy
Pro Avoidance of noise and dusts associated with traditional construction
Pro Can provide thermal mass if exposed
Pro High level of decrement delay is possible to shield from summer heat
Pro Airtightness is easily achievable
Pro Thermal bridging is very much reduced or eliminated entirely
Pro Requires only limited site skills
Pro 'Dry' construction prevents moisture from being admitted into the building
Pro Exact dimensions can be provided for custom / non-standard window and door openings
Pro Loads such as wall cabinets can be located without the restrictions associated with other forms of construction
Pro Prefabrication reduces the quantity of waste associated with onsite fabrication
Con Relatively new form of construction in the UK
Con Inflexibilitly- all design issues need determining ahead of fabrication. Any variations on site are very difficult and expensive to resolve.
Con Not usually for the inexperienced designer - however manufacturers usually provide considerable support
Con Inflexibility - future transformation of structure is more difficult than traditional construction
Con Requires external cladding and, usually, added insulation.
Con Longterm stability / movement needs needs early consideration
Con Services need careful consideration ahead of fabrication if exposed surface finish is used / routing is required. Service are difficult to relocate once the panel is installed.
Con Current overseas fabrication requires road transport over distance, adding significant embodied energy
Con Site usually requires crane access which might be difficult on tighter sites
Con High environmental impact glues tend to be the norm - but more benign options are available
Con Material cost - CLT floor slab can be around 2x expensive than a pre-stressed concrete hollow floor slab