not counted in LCAs for timber. Therefore only the electricity of the sawmill has to be taken into account: approx. 0.9 MJ/kg (Gopalakrishnan et al. 2012).
Issue 5, The issue of allocation
There are many byproducts (Fig. 6.1a): (1) byproducts of logging (wet wood waste that cannot be used for beams and planks) used for pulp and biomass (2) byproducts of sawing, such as sawdust, chips, and bark, that are applied in all sorts of wood products, like MDF and particle board.
In some literature on LCA, ‘system expansion‘ is recommended to deal with this specific case. A practical way to keep it simple is to apply the rule in ISO 14044, section 18.104.22.168 that “…outputs related to a combustible material can be transformed into energy…..by multiplying them by the relevant heat of combustion”, taking an MC of 50% (which is a fair average of practical rages between 30% and 70%), and a Lower Heating Value of 9 MJ/kg.
An alternative is to ‘cut-off” of the system at the stockpile of wood waste. In such an approach the wood waste is regarded as a final waste product of the production of timber, in line with EN15804. In such an approach the wood waste is free of eco-burden at the start of the production of byproducts like MDF and particle board: it does not make sense to carry over part of the eco-burden of timber to its byproducts. It is also in line with the way to deal with downcycling