Recent visits, to a number of sawmills across Wales, as part of the Home-Grown Homes Project, have brought to light the issue of large diameter ‘oversized’ softwood saw logs being chipped to provide biofuel. Some of the Welsh sawmills we visited report being unable to obtain these ‘oversized’ logs which often form part of larger lots being sold. These logs often end up with the larger sawmills who are unable or unwilling to process them into structural or joinery grade timber or with companies producing biofuel.
Woodknowledge Wales believes that in a declared climate emergency where possible logs should first be converted into products that store the biogenic carbon in the wood cell wall in the environment for as long as possible. This means converting logs to products such as structural grade timber, window, doors, stairs, skirting and floorboards, panel products and wood fibre insulation. Firewood and bio-fuel products are valuable co-products of the timber processing industry. However, we believe that suitable logs should first be converted into products that will store that carbon in the build environment rather than it being immediately released.
Wales has lost much of the culture and expertise of converting large diameter sawlogs into high-value products. Large mills are very good at producing structural grade timber, for use in house manufacture, at high volumes and low margins. This makes it very difficult for smaller sawmills to enter this market. However, there are niche markets for structural timber where small sawmills do very well and increasingly there are opportunities to enter the joinery sector. Saw – Dry – Rip (SDR) is a sawmilling technique, used widely in other countries which allows oversized and other logs deemed ‘unsuitable’ to be converted into valuable products for the house building market.
Saw – Dry – Rip (SDR)
SDR is a common sawmilling protocol used in America and Asia for drying difficult timbers. The related European method of drying ‘en boule’ could be used here in Wales to produce stable high-grade softwood joinery grade timber from, ‘difficult to handle, oversized logs’ which are all too often finding their way into (subsidised) biomass boilers.
The technique is essentially very simple, logs are sawn into planks cut parallel to the trunk – known as ‘through and through’ sawing. The planks are then dried – often by being re-configured into the trunk shape with spacers between each plank to allow air flow. The planks are then left to dry – often outside or undercover for extended periods of time, depending on the species and end use requirements. After air drying the planks may be kiln dried to final moisture content before being rip sawn to final dimensions.
Across Europe, particularly in France and Germany saw-dry-rip is commonly used for converting hardwoods. While in Japan it is a method used to process both hardwoods and softwoods into highly valued products including traditional table-tops which are sold by specialist merchants for over £3000 per piece depending on their appearance. Defects such as disease and wormholes just add to the desirability. The Japanese use this technique to convert plantation timber such as red grandis and Spanish chestnut into valuable products -species considered to be unsalable here in the UK.
Here in Wales SDR or the related European method of drying ‘en boule’ can produce stable, high grade softwoods. Many of the sawmills visited during the Home-Grown Homes Project were using horizontal head rigs which are particularly suited to cutting through and through. These mills could convert currently under utilised and under valued oversized softwood logs into valuable joinery sawnwood. This is a simple step for SMEs, needing little investment and capable of producing homegrown softwoods for high-value applications.
If you are a sawmill in Wales and are currently using this technique, we would love to hear about your experiences. To find out more or register your interest in attending a workshop on the topic, please contact Ceri.Loxton@woodknowledgewales.co.uk
Click here to read a short technical article by Dainis Dauksta on Saw-Dry-Rip