Bifold doors are made of several sections, which are folded open. They are usually wooden, but often incorporate glass as well. Bifold doors are commonly used for closets and between interior rooms, but they are occasionally used for exteriors as well. Fitting an external bifold door is similar to fitting an internal bifold door. If you are building a house or addition from scratch, you can actually create the door space based on the size of door you prefer. If you are replacing an existing door, the door set will have to match the space.
Check the height and width of the door space with the tape measure to make sure it matches the size of your bifold door. Bifold doors will actually be slightly smaller than the door size to accommodate the double fold. Check with your distributor or refer to the package to make sure you purchase a door that fits. If the space is small, you will only need one door kit.
Install the track and bottom pivot bracket that came with your bifold door kit. These will all be slightly different, but the track will need to be screwed in overhead and will have a pivot bracket for each door (whether you use one, two or more doors will depend on the size of your door opening). Use the straightedge level to make sure the track stays the same distance away from the edge of the wall along its entire distance. After installing the track, attach the plumb bob to the track to find where to install the bottom pivot bracket. The bottom pivot bracket should be in line with the pivot bracket on the track and will most likely be screwed into the floor and door frame.
Install the pivots into the doors. These will likely be a small metal bolt encased in plastic and set with a spring. Your doors may come with holes pre-drilled, but if not, check with the manufacturer's instructions to know where to drill the holes. After you've located or drilled the holes, tap the pivots in with a hammer. Pivots should be on the top and bottom of each door where it joins with the jamb and header. The outside of each door will also have guide pivots. Refer to the manual to identify these pivots so they all get put in the right place.
Fit the lower pivot into the pivot bracket. Depress the upper pivot to fit it into the pivot bracket on the track. Check to make sure the door is straight with the level. Adjust the distance between the door and door frame by moving the lower pivot into different slots on the pivot bracket. The top pivot can be adjusted by loosening the set screw on the top bracket, moving the pivot the desired location and re-tightening the screw.
For external use, install a small piece of trim on the outside of one of the doors. This will keep the doors shut and minimise heat loss. If the trim was not already installed with your door kit, match up the trim piece so it sticks out over the edge of the door and nail it in with small finish nails.
Make sure the door kit you purchase matches the space you have for your door. You will most likely not be able to adjust the size of the door after the fact.
Bifold doors do not retain interior heat as well as traditional doors. If you are using external bifold doors for a porch or in a consistently warm area, this may not be an issue.