I could/should have made this code more robust. But it was not necessary for the test input, so I guess it is sufficient for what the Kata author intended.

Wrong! Everything with value below 'Z', that is 90 will be precedeed by a space. Than includes numbers, special characters as well as spaces.

I disagree, it's only false the first time, but it needs to be checked for each letter. Not needed, since we can add the "-" for each loop, and just remove the last char from the StringBuilder. Check my solution.