Storytelling Carbon Performance vs. Targets/Benchmarks: Reuse Projects

Where you have a reuse project – a project refurbishing an existing building to renew the utility of a space – how do you present your WLCA results against the common industry benchmarks and targets?

For example:
We have various London targets/benchmarks available (LETI, London planning authorities, etc.). LETI in fact states that it assumes some degree of reuse in its benchmarks; GLA doesn’t state that explicitly, so presumably that means its benchmarks are for 100% new builds.
We do an LCA for a project which is reusing extensive amounts of substructure, facade, etc. Compared with the LETI and GLA benchmarks/targets, it will be very low.
One way we can look at it is to come up with finger-in-the-air %s, to describe how much retention there is in different categories of the assessment (e.g. approximate that 75% of the structure is retained); and we reduce the relevant benchmark sub-categories by that amount (e.g. if 75% of structure is retained, the revised structure carbon budget is 25% of the new-build budget).
HOWEVER, that finger in the air exercise is incredibly crude, and probably skewed by the fact that we better understand VOLUMES being retained, vs. CARBON being retained. So I don’t like it at all.

I am preferential to not adjusting benchmarks, and simply showing project WLCA performance against the unadjusted targets/benchmarks. The positive story in this case is that you are achieving a certain amount of useful/valuable/renewed space, without building new. The downside to this strategy is that the WLCA will look brilliant / like the project is performing really well, so there is little motivation to continue to pull together and reduce carbon further.

Thoughts?

I agree that benchmarks should not be adjusted for re-use. It should be that the benchmark continues to be lowered over time, and we as designers realize the only way to completely avoid carbon emissions is through re-use!

It would still be valuable to also benchmark against the project’s business-as-usual. Even with re-use, there will be introduction of some new materials, how can those materials be improved upon? I.e., setting benchmarks at material level through EPDs vs. at the project level through available benchmarks.

My understanding is that for the LETI target alignment with SCORS, that the only way of getting an “A” rating currently would be through re-use: https://www.leti.uk/_files/ugd/252d09_a45059c2d71043cdbcffc539f942e602.pdf