Mysest56 
November 19, 2022
No one likes the feel of a supposedly good floor bouncing or sagging underfoot. A springy or spongy feeling could indicate a minor problem, a significant issue or no problem at all. As soon as you identify the issue, you may have the ability to repair it yourself. Some corrections, however, require the help of construction and engineering professionals.
Loose Subfloor
A spongy feel underfoot might demonstrate that the subfloor isn’t securely attached to the floor joists. This condition permits the floor to give slightly when you measure. If the issue is beneath carpeting, you can roll back the rug and pad, insert 2-inch decking screws 8 inches apart from the subfloor over each joist and then reinstall the carpeting. If the issue is under a linoleum floor, you can’t run screws to the flooring surface or you will hurt the linoleum. If you can get the joists in the crawl area, fill the gap between the top of the joists and the underside of the subfloor completely with subfloor glue and then put heavy weight on the floor above for at least 48 hours. If this doesn’t repair the issue, the next step is to screw the subfloor down from over and put in new flooring.
Overextended Joist Span
Floor joists which span a space greater than they need to can also cause a springy feeling when you walk across the room. Because the floor joists are a part of this house’s structural weight-bearing system, consult an engineer prior to making alterations. Among the simplest ways to repair the joist length is by “sistering” the floor joists from beneath. This entails cutting fresh joists and attaching them to the present joists to boost their stiffness factor. Another method is to set up ticking between the present joists. This entails cutting dimensional lumber to fit perpendicularly between the present joists. The “bridges” run from one end of the joists into another, usually in the center of the joist span. When you walk to the floor above, the bridging moves your weight to the next joists and somewhat stabilizes the rebound. A final resort, but maybe the best alternative, is to put in a perpendicular load-bearing beam in the crawl space. The place, beam dimensions and way of supporting the beam must be determined by a structural engineer.
Floor Trusses
Floor trusses rebound; there’s just no way around it. Floor truss makers call it “deflection,” and they maintain it’s normal. Unlike floor joists, which are strong, trusses are engineered with smaller associates in a triangulated design which permits the relatively lightweight trusses to keep up as much or more load as conventional floor joists. Any alterations you make to a floor truss system can void the manufacturer’s guarantee and will conflict with the program’s pre-engineered load distribution. Because the floor is not going anywhere, the best solution is to get used to the rebound. The only alternative is to request the truss manufacturer for an engineered service solution, but typically you are unlikely to receive you.
Delamination
Subflooring typically is made up of plywood or oriented strand board (OSB) sheets. Both of these products make sound subfloors, but should they become saturated, through leaky pipes or flooding, the glue that holds them together discharges. Called “delamination,” this causes the sheet to swell and become spongy underfoot. The only solution for delamination is entire replacement of the damaged subfloor sheets. After delaminated, plywood and OSB lose their structural integrity and therefore are no more safe or effective.