off-site

Both off-site and off site are correct in different circumstances.

E.g. "I am taking the car off site."

"Fred's not here because he's an off-site worker"

Both off-site and off site are correct in different circumstances.

E.g. "I am taking the car off site."

"Fred's not here because he's an off-site worker"

Kingspan Off-Site was created in 1947.

You are supposed to hyphenate compound adjectives. Off-site Data Center. Off-Site is an adjective that describes the Data Center. It can be an off-site data center or a data center that is located off site. The only exception is if the first adjective ends in "ly" like highly recommended. Which off-site data center does not. See the Wiki. Another way to remember it is you can't have an "off" data center or a "site" data center. You need the hyphen to connect off-site in order for it to describe the data center.