I was asked to evaluate a subfloor in a 1968 house. The home inspector for the buyer flagged the subfloor as inadequate due to the 4-foot joist spacing. I admit it was a WTF moment when I saw the photos in his report. Once I arrived today I got a closer look. The floor joists were double 2x10s with 1/2" plywood in the middle. The joists were spaced 4-foot apart with a 1 1/4" Sturd-I-Floor tongue & grove plywood subfloor. I had never seen this before in my 30 years of inspection.
Using the current engineering guidelines for the condition assessment of existing buildings I have to evaluate the subfloor based on building codes in effect at the time (1964 Uniform Building Code) along with material properties commonly used at that time. Turns out it passed, however over time all floor joists will have additional deflection called creep that’s usually 1.5 to 2 times the initial deflection. The house was vacant and just walking on the floor there was very little noticeable deflection.
