Bi-fold doors – which fold in two when opened and are therefore extremely useful when space is too limited for a fully opening door – generally speaking will support themselves on their hinges. You need, of course, to install a jamb over the top of the opening frame. A door jamb will ensure the doors close nicely and don’t strain the hinges, and also allow you to line up the floor bolts easily. It’s important to take care when installing the door furniture to avoid any clashes and subsequent damage to the doors themselves when folded back.