Why Timber?

It is well known that timber is the only renewable construction material, whose resources can be expanded and replenished through sustainable forestry management. In fact, in managed forests across Europe, there are 5 trees planted for every one which is harvested (Wood for Good). Trees are also sometimes referred to as the lungs of our planet, whose growth is the very mechanism by which the increasing amount of CO₂ is taken out of the atmosphere and is replaced by oxygen. What you may not be aware of is just how powerful the CO₂ sequestration of trees is: in a metre cube of timber building material, approximately a tonne of carbon is stored within the building fabric.

Why Mass Timber?

With this in mind, how can we increase the amount of timber used in buildings to store more carbon in the built environment fabric? The answer lies with engineered mass timber products, which instead of the typical timber frame system utilise multiple layers of timber, laminated (joined) using glues or mechanical fasteners to form solid timber panels or beams. There are several types of mass timber products:

Which System?

• Glue Laminated Timber: Glulam is comprised of a number of layers of dimensioned timber that are bonded together with structural adhesive to increase structural performance. Generally, the grain runs parallel to the main axis of the member. By laminating a number of smaller timber elements, a single larger strong structural member is manufactured.
• Cross Laminated Timber: CLT is manufactured from lower grade timber off-cuts which are reduced to strips that are finger-jointed and glued in perpendicular layers under high pressure. In the factory, the solid CLT panels can be cut to the required shape and size.
• Laminated Veneer Lumber: LVL is manufactured from thin, peeled veneers of wood, usually 3mm thick and glued with structural adhesive. Panels of LVL are cut into structural members, which have high strength and stiffness.
• Dowel Laminated Timber: Dowel-Lam (or Brettstapel) is fabricated from softwood timber lamellae stacked in one plane and connected with hardwood timber dowels. This relatively simple manufacturing method has the potential to utilise lower grade timber (that would otherwise be unsuitable for use in construction) to form load-bearing solid timber wall, floor and roof panels.
• Nail Laminated Timber: NLT is similar to Dowel-Lam, however nails are used to connect the timber planks into a solid wood panel.

Massive timber products can be utilised in many different building types, however given their inhernet strength they are most advantageous in building larger building structures – either as the main superstructure material or in combination with other building systems to form hybrid construction methods. To find out more about solid laminate timber systems, you  can read the new book ‘Mass Timber – An Introduction to Solid Timber Laminate Systems’ by Dr Robert Hairstans

Additional resources 

Wood for Good

This blog post was written by Mila Duncheva and Dr Robert Hairstans, from the Centre of Offsite Construction and Innovation Structures at Edinburgh Napier University.