I don't think 'layman' is an offensive term by any account. If you go by [OALD][1], it says...

> a person who does not have ***expert knowledge*** of a particular subject

So, the term 'layperson' separates a common person from an expert. And, being a 'common man' here does not offend you or me at all. 

The example down there puts light on it

> a book written for ***professionals and laymen*** alike 

But I *do* think that replacing it with 'ordinary' ***may*** get a few (including me) some note of offensiveness. I'd use *common* over *ordinary*. 




  [1]: http://www.oxfordlearnersdictionaries.com/definition/english/layman