Hi Xavi,
Getting exact numbers for CLT and all mass timber is difficult given our current data. I would be lying to say that I have a perfect understanding of the entire issue, but maybe I can start to help and someone else can jump in to fill in the gaps. CLT has a wide range because the carbon accounting for wood can be quite complex - to illustrate this point, the CLF has a seven part series discussing carbon in wood, linked here:
There’s a lot of questions about biogenic carbon, forestry practices, the health of forests after logging, the regrowth of forests after harvesting, and the amount of carbon that remains in the soil. I see that you removed biogenic carbon from the numbers. This helps clear up some of carbon questions, but it means that the wood isn’t receiving any credit for sequestered carbon, so you’re left with the carbon intensive process of harvesting, milling, and producing the CLT panels.
You’re not alone in noticing that CLT can perform as poorly as concrete. I’ve seen reports from Miller Hull and MKA both looking at the range of carbon in mass timber, and they’ve also identified that CLT can range from being much better than concrete to being equal. My understanding of these studies is that the general belief is that CLT will perform better than concrete, but sourcing the wood from well managed forests is key. Maybe @iancho or @ddavies can weigh in on their studies.