Sectional garage doors are those which consist of several panels. They usually have around three or even more panels and these panels are hinged together and attached to the sides by separate brackets. In contrast to one piece doors, the panels of sectional doors can be replaced independently. That's the convenience of having sectional doors! Often the bottom horizontal panel is the first one to wear as it is found at the lower part of the door.
When one of the panels is hit by the car or ruined for any other reason, it must be replaced. The easy part is that the damaged panel is the only one removed and its perfect match is installed in its place. It is certainly a hard task since it involves removing the brackets, releasing spring tension, removing the hinges and finally the panel. The same steps must be repeated backwards to install the new panel. It's a rather complicated, delicate and at times dangerous procedure and it's best to be done by expert contractors.