basic homes typically have bedroom or bathroom doors at 30

inches frame to frame, and that's also typical size for bath tubs. That's why the 1 piece unit is in before the door frame is built. Although the door opening is 30 inches, there are door stop pieces around three sides of the door frame that make the actual door opening about 1 inch smaller than 30 inches. In this case you can not replace the 30 inch wide tub with an idential 1 piece tub and surround, without taking out the door and removing the door stops.