Jadnashua
Retired Defense Industry Engineer xxx
Blocking, especially the type usually installed (diagonals or solid often with a gap and not tightly fitted) primarily help keep the joists from twisting, which helps them maintain their maximum strength, but does not signficantly aid in overall floor deflection ratings. If you put a dead load on a subfloor with and without blocking, and it will deflect nearly the same. WIth properly installed subflooring, you get sharing between adjacent joists. Deflection is still a concern in a general case. Testing has shown that blocking does not make a major contribution to deflection except prior to subfloor installation. As previously noted, failures can often take up to 10-years to exhibit themselves from failing to follow the rules. There are short-term effects, and long-term creep effects. An improperly spec'ed floor under a heavy continuous load will slowly bend, different from a short-term impact, and can eventually fail.
There's a lot more science in this than the average person is aware of. Most pros give a 1-year warranty, and may fix things after, but often not. A failure after that timeframe, people don't often associate it with the install.
The trend in specifications for a floor is leaning more towards design for the real dead load than specifications on live load deflection...this is more reliable in the long-term and only slightly correlates to the current deflection scheme.
If your joists are fir or southern yellow pine in good condition, you should be okay. If they are full of holes, splits, or cracks, and another species, they are not.
There's a lot more science in this than the average person is aware of. Most pros give a 1-year warranty, and may fix things after, but often not. A failure after that timeframe, people don't often associate it with the install.
The trend in specifications for a floor is leaning more towards design for the real dead load than specifications on live load deflection...this is more reliable in the long-term and only slightly correlates to the current deflection scheme.
If your joists are fir or southern yellow pine in good condition, you should be okay. If they are full of holes, splits, or cracks, and another species, they are not.