Knott Laboratory provides forensic engineering and animation, Civil & Structural, and Fire & Explosion Investigation services to reconstruct accidents.

How to Repair Sagging Floors in Older Structures?

These issues often involve structures that have been standing for 50+ years.

Published July 22nd, 2019

By Peter W. Korff, B.Sc.


example of crushing joist
Example of crushing joist


One of the most common inspections we perform at Knott Laboratory involves sagging or deflecting floor systems. These types of inspections often involve structures that have been standing for 50+ years. These investigations normally begin with a call to investigate distresses and cracking in the drywall or other interior finishes of a structure, as this is often the first sign of deflecting floor systems. One of the first thing we observe during these inspections is the size, spacing, and span of the floor system joists. Often in older buildings, we find the floor system to be under designed in comparison to today’s codes and design standards. This means that the structural members intended to support the floor system are not considered to be strong enough by todays standards to support the loads they are intended to. While the structural members may have supported the loads for 50 or more years, they are now beginning to deflect. This deflection over time is referred to as “creep” in the engineering world. Along with creep, we see crushing of joist ends which can result in deflection of the floor systems.


elevation survey
Example of Elevation Survey


At Knott Laboratory, we have the ability to thoroughly investigate and design repairs for cases involving deflection of floor systems. These investigations often involve the completion of an elevation survey of the structures flooring system to determine where in the structure the flooring system is deflecting. Along with elevation surveys, Knott Laboratory uses third-party contractors to conduct destructive testing in order to observe the as-built condition of the building and obtain joist sized and spans. Following the gathering of the needed information, Knott Laboratory designs repair plans to correct or at the least stop the deflection from worsening. Through thorough investigation and experience in structural rehabilitation, Knott Laboratory’s engineers have gained the skills and experience to investigate and design repair plans for deflecting floor systems.


example of drywall distresses
Example of Drywall Distresses