Validation has been suggested, but I would like some advice on exactly how to respond to her.
Unfortunately, there is no magic formula~~no exacts because everyone is different and each situation may call for different responses. BPD is complex and there will be times when your wife may respond differently although you are doing the same thing.
This may not sound all that encouraging, but there is hope! Take time to read the lessons on validation and I'd highly recommend watching the video (link below) I found it extremely helpful in understanding the concept of validation.
www.youtube.com/watch?v=EDSIYTQX_dk&feature=youtu.beAs for the issue with your house... . you'll find that many folks here speak of similar issues. BPD's have a hole that they want to fill and they look for and expect an outside source to fill it. Validating what is
valid is key (I understand that you feel this house is a dump) but not validating the invalid (the house is the source of her discontent).
I hope this helps somewhat. Validation takes time and it's a learned skill. Keep practicing!