Prenups can say (almost) whatever you want, so the short answer is to cover maintenance expenses in the same document that gives you a stake in the property in

Prenups can say (almost) whatever you want, so the short answer is to cover maintenance expenses in the same document that gives you a stake in the property in the first place even if that stake is just a residence one. Of course that's much more obvious in hindsight but there's also postnups which can amend the prenup. If I were pitching in to renovate a property I'd want equity in it. You can do that with or without the inheritance or the prenup: figure out the value of the property before and after the renovations and assign that percentage to the person that covered them. That's what I'd do in a non-romantic housemate situation but of course a marriage is way more complicated and there are lots of pieces that aren't purely legal or equity in nature. A prenup isn't going to absolve you of that.