A floor that bows in the middle, flexes noticeably, or dips down in one or more areas could indicate a serious structural problem with the foundation and/or framing.
An unstable floor can have several causes. First of all, old-time carpenters may have used undersized floor joists because they were building before engineered span tables and building codes were available. A joist that spans a long distance without being supported in the middle is likely to sag or flex.
Floors can also sag or flex because a beam installed to provide mid-span support for joists has shifted out of position or rotted. 
An experienced foundation repair contractor can diagnose bouncy floor problems and perform foundation repairs that make the floor framing stiffer and more secure. The SmartJack system, available from Foundation Support Works dealers, is an excellent solution to many bouncy or sagging floor problems. As shown in the photo and drawing, the SmartJack system has two main components: a precast concrete footing and a steel jack equipped with a threaded rod and a steel top plate that fits under a beam or girder.
Unlike an old-fashioned wood post-and-beam framework, the SmartJack system is adjustable, enabling the contractor to fine-tune the height of the support beam and thus, the floor itself. With a series of SmartJacks installed beneath a sound mid-span support beam, an unstable old floor can be made stronger, stiffer and straighter.
Contact Alpha Foundation Specialists today for a Valdosta, Tallahassee, or Gainesville foundation repair company!