The approximate opening should be 49 by 82 for a 48 by 80 inch door. Generally, the rough opening of the folding door should be 2 inches wider and 2 inches taller than the door itself, regardless of the size of the folding door. If the folding door is to be installed in an opening wrapped in sheets, the approximate width of the opening must be adjusted to the actual width of the folding doors (48 in the case of this example). The finished opening of this size for a folding door will allow you to install a jamb kit or use selected ¾ thick wood to create the finished door jamb.
Keep in mind that these guidelines for finishing the opening of a folding door are typical frame standards used in the homebuilding business. Normally this isn't much, but if the rough opening is airtight or the exact size of the door and jamb, the door may not work properly without having room to adjust. If the vertical plane of the wall is mostly plumbed and the door fits in the hole, you may still be able to use the brackets. Again, the folding closet door opening must first be trimmed and therefore taken into account when sizing a rough folding door opening.
If the rough opening isn't the right size, the folding door won't fit if it's too small, or it'll have wide gaps if it's too big. Therefore, the finished opening of the folding door should be 1.5 inches narrower than the rough opening of the folding door, due to the installation of the finished moldings. This will allow the carpet to be hidden under the jambs and usually leaves enough free space so that the door doesn't rub against the carpet. The final opening for folding doors involves attaching 1 inch x N molding boards to the 2 × 4 frame bolts of the rugged opening folding door.
Always check the manufacturer's or product specifications to confirm the approximate opening requirements for your particular folding doors. Most standard interior and exterior doors have the same approximate opening width, but some manufacturers differ in height between the two. Keep in mind that most folding door sets don't come with a door frame kit, so it's quite common to use ¾ thick selected wood to create the finished door frame. The sets of mechanical supports for folding doors are actually bolted to this finished door jamb, so it is important that the jamb is installed plumb and level.