When making material and assembly comparisons that take into account service life, it seems like the 60 year period is kind of short to give an accurate representation, i.e. a product that lasts 30 years gets counted twice, while a product that lasts 50 years also gets counted twice. It seems like extending the LCA period to 100 years or more would help alleviate that. Although making replacement assumptions far into the future seems unrealistic, even for a hypothetical calculation. Does anyone have any thoughts on this?
If we are going to leave the LCA period at 60 years and a material’s expected service life is assumed to be, say, 50 years, does it make sense to round it up so it’s not penalized in a comparison against materials with a much shorter service life?
I understand the reasoning for making material comparisons with only Stage A/ upfront carbon, and it avoids the uncertainty about Module D and how long things will really last, but it seems wrong to ignore the benefit of choosing materials that last longer. Perhaps this only comes into effect for applications where there is a wide gap in life span, i.e. asphalt roofing vs metal roofing.
Hi Scott. You are correct that there’s some oddities to the accounting for replacement cycles. However, extending the life span may only increase the uncertainties. The replacements in module b are tracked as a replacement of the same material with the same impacts. It’s hard to believe that future materials will have the same impacts, or even be the same materials, as the ones we use today. The further out we push our predictions, the less likely it is that our assumptions on material replacement will be accurate.
As for the end of life assumption - if a building owner is replacing a 50 year roofing material, but assuming that the building will only have 10 more years of life, they may opt to replace the longer lived material with a shorter cycle material, or they may find that extending the life of the roof may extend the life of the building. Regardless of what material they choose, that material will incur an embodied carbon cost, so while it might not be entirely accurate, it’s not unfair to apply the full carbon emission impacts to the selected material.
That isn’t to say that we can’t find guidance from looking out into the future at replacement cycles. We can use these studies with a bit of outside judgement to weigh the outcomes. For instance, we may choose a higher impact material only needs to be replaced once vs a lower impact material that needs to be replaced several times because there are additional benefits. You’re reducing raw material needs, you’re reducing the burden of repair for the building owner, you’re pushing the new carbon emissions for replacement out into the future (future carbon emissions should be weighed less than current emissions). The LCA results are a guide to help test assumptions, but shouldn’t be absolute.
Hi Scott, just adding my thoughts here …
60 years is not an LCA standard. Its probably the most typical value I’ve seen but ASTM E2921-16a recommends 75 years and the Finnish reporting requirements recommend 50 years. So there is so variability.
We typically report upfront (A1-5) emissions too because there is significantly more certainty in these values and reducing emissions now is the most important task.
What I also try to do, but I don’t do it consistently, is to run the numbers for 50, 60 and 70 year building life and just compare the numbers and see if anything is jumping out. Consider it a sensitivity test