If I have a 14-day extension for handing in coursework does that include when the university is closed?

No, any days when the uni is closed don't get included in a revised coursework submission date if you have a successful 14-calendar-day extenuating circumstances (EC) claim. 'Calendar days' are every day of the week including Saturdays and Sundays but exclude when the university is closed such as public holidays and Christmas. See full term dates and university closures days online.