Need help creating a function for character string creation in R

It would be helpful if you could provide a sample of the actual data frame you're working with, including it's structure (you can use for example dput(my_data[1:5, ]) and paste the output into your question to provide a data sample, or use the reprex package to provide a full reproducible example of your data and code).

By any chance are the building codes actualiy stored as numeric values in your data frame?
For example, run the following at see the output in the console:

paste0("16.10", "_1")
paste0(16.10, "_1")