Compound adjectives. Hyphenate most compound adjectives that precede a noun, but not those that follow a noun.
a well-liked boss | My boss is well liked. |
a six-foot plank | The plank is six feet long. |
In general, the reason for hyphenating compound adjectives is to make meaning clear.
Without the hyphen, living may seem to modify room dividers.
Never hyphenate an -ly adverb and an adjective.