You live in Ireland dear boy. Which is about the same temperature as most of the rest of the southern British isles. Come back when you actually live somewhere where the ice forms on the inside of your windows, even with the heating on, and it's -30 during the day.
Do you have a TV? If so does it still work? If yes then there is no issue with condensation. Computer parts will survive easily at 0 degrees, and if you are planning to water cool the comp then if that freezes up you'll have bigger issues, such as all the pipes in the house, which will probably burst at the same time.

Do you have a TV? If so does it still work? If yes then there is no issue with condensation. Computer parts will survive easily at 0 degrees, and if you are planning to water cool the comp then if that freezes up you'll have bigger issues, such as all the pipes in the house, which will probably burst at the same time.