We looked into this with a completely open toolchain [0]. You could email either of the two first authors to get the code (not sure why it wasn't in the paper supporting information).
Building open carbon models isn't difficult, it's the input data that normally require licenses. I have built an open source life cycle assessment (LCA) software which has some traction [1], and there are alternatives for LCA [2] and integrated assessment models [3, 4]. However, data availability, especially on the level of completeness and detail you need to answer a specific question like carbon performance of a structure over a given period of time is a challenge. We are working on building a large open database to answer these kinds of questions[5], and Hacker News readers are welcome. Happy to chat via email if you want more info!
[0] https://pubs.acs.org/doi/abs/10.1021/acs.est.5b01735
[3] https://github.com/JGCRI/gcam-core