hyphenation - Non-residential vs non–residential (short or long hyphen)

Should there be a short or long hyphen separating the two words?

Non-residential vs non–residential

Answer

tl;dr: Use the hyphen.

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I'm not sure EL&U typically addresses typesetting questions, which tend to be a matter of convention, stylistic choice, and or publisher mandate (i.e. house style), but this one seems fairly clear-cut.

According to the reference @Eilia supplied to the official Translation Bureau of the Canadian Government, there are three punctuation marks to consider:

• The hyphen: -


• The en-dash or "short dash": –


• The em-dash or "long dash": —

The hyphen is the character found on the underscore key (_) on the standard American keyboard¹. In the days of typewriters the em-dash was sometimes rendered as two hyphens (--), because the character is twice as long as the en-dash (i.e. the width of a M rather than an N), and every once in a while you'll see that convention used on the internet. But by-and-large today, both the en- and em-dashes are supplied by specialized desktop publishing software.

Let's dispose of the em-dash first. The em-dash is used exclusively for emphasis: a pair of em-dashes surrounding a clause are sort of like "negative parenthesis" — they draw attention to the clause, rather than downplaying it.

By contrast, both the hyphen and the en-dash are used to form compound modifiers, which is what you're asking about here. But the en-dash is only used to form compound modifiers when one of the components itself is compound, as in "post–World War I treaty", "sodium chloride–free solution", or "New York–based writer".

It is the hyphen which is used to form standard two-word compound modifiers such as "non-residential"².

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¹ _{aka ANSI-INCITS 154-1988 (R1999)}

² _{Note that you only use the hyphen to form the compound modifier if that modifier precedes the word it modifies, not if it follows. In other words: "on-site facilities" but "facilities on site" (no hyphen nor dash).}