Glulam is well accepted as a versatile and technically advanced material for demanding wood construction. Its exceptional strength makes it especially suited for use in the load-bearing structures of buildings with long spans when architectural beauty and a strong sense of space are sought.
One exciting development in the evolution of glulam is the application of Thermowood technology to the material. Thermowood, known in application to other timber materials, involves treating timber at high temperatures in special kilns. This results in a more stable and durable timber, bringing hardwood performance to softwoods.
Improved insulation
Heat treatment alters the cellular structure of the wood, reduces the equilibrium moisture by up to 60% and renders the wood less susceptible to re-absorbing moisture from the air. This treatment has a number of benefits. Firstly, it removes most of the natural sugars and resins which can act as nutrients for decay-causing bacteria and the expulsion of water means that the wood is less prone to warping. The treatment also improves the insulation properties of the timber; and makes it 15% lighter – thereby much easier to handle on site.
Standard species which have proved suitable for this form of treatment include spruce and pine, which achieve durability Class 2 of 5 – and so warrant the definition ‘durable’. This compares favourably to Californian redwood, European oak and juniper. Heat treated timber is also resistant to attack from insects such as longhorn beetle, furniture beetle and powder-post beetle as outlined in European Norms (ENs) 46, 21 and 20 respectively.
Furthermore, the improved stability of Thermowood, with its lack of resins, increases the life expectancy of any applied surface coating systems by as much as five times; although for optimum performance translucent or opaque exterior stain finishes are recommended.
Chelsea Flower Show
The world’s first appearance of Thermowood glulam was at the RHS Chelsea Flower Show in May. Finnforest UK provided the materials and sponsorship of a bronze medal winning show garden on behalf of Shelter, the leading charity tackling homelessness.
In the ‘Shelter Garden’, designed by architect Jeff Dutt and Philippa O’Brien, a raised wooden A frame structure was built from Thermowood glulam. The A frame structure was intended to emphasise the link between the house and the garden, and provide a low-cost architectural structure with space for the whole family. The top floor formed a children’s play area, while the lower level was set aside as a space for entertaining.
The A frame consisted of engineered timber beams constructed from a minimum of four laminates, glued together horizontally and machined to the desired shape. The frame was built by Cowley Timber Engineering which was, in Mr Dutt’s words, “amazing”.
Increased rigidity
As an architect, Mr Dutt was drawn to Thermowood glulam for two main reasons, based on benefits delivered by Thermowood over and above those traditionally associated with glulam. Firstly, as mentioned, the treatment significantly reduces the weight of the structural elements – making site handling and erection much easier. Similarly, the Thermowood process increases the rigidity of the glulam beams. As a consequence, deflection is reduced – and so a slimmer beam section could be employed.
The commercial potential of Thermowood glulam has yet to be assessed, not least as it will need to be subjected to testing and accreditation for its structural suitability; but its appearance at Chelsea is cause enough for some eager anticipation as to when this occurs.
This is the first time Finnforest has sponsored a garden at Chelsea and, by working with Shelter and the garden designers, it was able to realise a beautiful garden concept that not only looked stunning and could deliver an affordable and accessible building design template; but also heralded the potential evolution of how glulam is handled and deployed.
