Extension spring systems use springs that stretch and retract to close and open your garage door. As the garage door closes, the extension springs which run along the horizontal track on each side of the door expand and are under great tension. Operating cables attached to the bottom of the door on either said offer counter balance strength. Safety cables help contain the springs in the event they break. As the door goes back up, the springs retract using that strength to pull the door to the open position.
Extension spring systems come with their own pros and cons. One advantage of this system is that each side of a spring system works independently to compensate for uneven ground. On the other hand, they require more parts, such as the pulleys and operating cables, and usually need more maintenance.
Older homes typically use extension systems because they have limited headroom in the garage, which is needed for a torsion system. Headroom is the available overhead space over the door height, and varies for each garage. However, any home, regardless of age, requires a minimum amount of headroom to transition to a torsion spring system.