Many users who are recommending the use of large PV systems or cross-laminated-timber in place of concrete are finding that the increase in ADP or ODP is above the Green Star allowance of 10% which is causing the project to lose their whole Greenstar LCA credit. We have previously suggested some measures specifically for large PV systems to help reduce the % of increase in ADP/ODP for those only marginally over the allowance. However for some larger systems and CLT recommentations, these measures are not enough. In light of this growing concern, we thought it would be important to address the underlying issue regarding ODP & ADP increases for what we believe are the best choices for the planet and hope to shed light on these questions.
Firstly, it is important to not miss the wood for the trees on this issue. The relative percentage increase of an indicator is not a good representation of the net environmental gain or loss. For example, 10% improvement in one indicator and 10% performance loss in another would rarely “cancel each other out” due to the following factors:
- The “business as usual” or “reference case” design may have far more significant levels of one indicator verse the other. For example, it may be that the design has very minor levels of indicator A but much higher levels of indicator B in which case a small percentage drop in indicator B would be more significant than the same change in indicator A. In LCA this problem is addressed with normalisation (expressing each impact as a % of a typical person’s impacts giving a relative magnitude compared to “normal” levels). From ISO 14044: “The aim of the normalization is to understand better the relative magnitude for each indicator result of the product system under study.” It is not possible (or at least very difficult) to understand the relative magnitude of indicators without normalisation.
- The actual relative damage of each environmental impact may be quite difference, for example small amounts of one indicator may be far more damaging than larger amounts of another indicator. This is normally addressed with weighting. From ISO 14044: “Weighting is the process of converting indicator results of different impact categories by using numerical factors based on value-choices. It may include aggregation of the weighted indicator results.”
The GBCA calculation technique for assigning credits to the LCA outputs ignores normalisation and weighting and hence should not be used for making design decisions. The GBCA method aggregates results before any normalisation or weighting is conducted which is almost certain to result in adverse design decisions if used to assess the relative merits of design options particularly where there are trade-offs. For example avoiding larger PV systems or choosing concrete instead of CLT.
eTool have expressed this concern and have provided real life examples of flaws in its application in previous public submissions to the GBCA. You can read about our submission in the link below which summarises our feedback to the GBCA during the public consultation for the V1.2 credit. If you also believe that it is unfair to penalise projects for having large PV panels and using CLT, we highly encourage the eToolLCD community to lobby the GBCA to tackle this issue. When situations like this arise, a Credit Interpretation Request (CIR) needs to be raised with GBCA to discuss about a potential alternative pathway. Please get in touch with us for assistance normalising and weighting your results which may support a CIR for the GBCA (this has been a successful avenue for some other users historically).