You can indeed fit bi fold doors - the trouble is they can't really be made secure, which could be a problem as they are generally meant for wardrobes etc. They fit in exactly the same way as ordinary wooden doors i.e with usual hinges but they do occupy a fair amount of space, even when folded. A way out of this could be to remove the door completely or fit a sliding door if you have the space?
John, April 2008
