We have a three story condo that was built in 1985. Although the second and third floors are not overly bouncy, there is a noticeable deflection in the engineered beech flooring and it squeeks and just feels like cheap laminate flooring, although it's a high quality German product.
Digging in to the problem, I have come up with the following observations:
1) the joists are 2X10, on 16" (maybe some are at 24") centers. Span of 12'.
2) the subfloor is a particleboard (not OSB) product.
3) the planks are running parallel to the joists
4) the engineered flooring is floating and laid on felt type underlayment.
5)The deflection I am noticing is not in every area, but just a few areas. However the noise eminates from most all of the walking area.
The apartment next door (same construction) has solid oak 3" planks and the floor is rock solid, and no sound of creaking when walked on. I am 99% sure that there was nothing done to strengthen the joists, like sistering.
What are my options to obtain a solid floor with minimal noise? Yes, I would like to re-use the existing planks, but not possible then I'm OK to replace with something more appropriate.