Pre Nups have no legal standing in Ireland
HOWEVER...........
You say you are in your 40s. You are getting married. Does family law apply to you? Yes, it applies to married people whether there are kids or not.
Ask yourself this question - does your spouse-to-be have his/her own property? If not, what would his/her expectation be about this house? That it would be where s/he would continue to live if you separated?
Did you not have any conversation about house ownership when you bought? Other that it is in your name?
Since you don't appear to have had the conversation back then, would you consider the prospect of having the conversation now? You may find s/he will be horrified that you are thinking like that - human beings have the most extraordinary capacity not to deal with issues but to shuffle around them
If you can reach an agreement on how the house/sale proceeds would be split, then record it in writing and both sign it. And after that, you should both go and see a solicitor each and ask for a letter confirming to each other that you've each had legal advice and understand the consequences of what you've signed
A Court would at least consider that in the event of a marital break up- maybe not as a Pre Nup but as an acknowledgement that one party put in a great deal more money than the other
mf