LEN does not count trailing spaces. If you want to know the length including trailing spaces you need to use DATALENGTH. DATALENGTH returns the number of bytes including any trailing spaces. But since VARCHAR is one byte per character, it will return 14 if you have 11 characters in employeeid and add three spaces.
However, you don't want to just add three spaces, since if employeeid is 14 characters long and you add three spaces,, it's now 17 characters, Depending on how you are using the result, that may or may not be a problem. I would recommend using
LEFT(employeeid + SPACE(3), 14)
as that will add 3 spaces and then truncate the result to 14 characters if adding the 3 spaces made the result more than 14 characters.
Tom