The why-to-for of spongy floor

A few things struck us as "we'll need to fix that eventually" when we first toured the cottage back in May. One item on the list was the sponginess of the kitchen floor. It was so bad that every time someone walked over it, the silverware in the drawer jingled. It wasn't until we pulled up most of the layers of the floor that we realized the cause. It's apparent in this photograph of the subfloor, after all layers of underlayment, linoleum, vinyl, foam, and veneer woodlike flooring had been removed:


The section on the left was original construction, the right side was an addition. It's easy to spot the demarcation point. In fact, it's easy to see where the original wall plate had been fastened to the subfloor deck. The original planking on the left had been laid properly, at about a 30 degree angle. I don't have a protractor handy, but I'd estimate the addition's planking was laid at about a 60 degree angle, which caused long runs across the floor joists. The planks visibly deflect when walked on; the situation wasn't much better when all the layers on top were present.

Al's ripping up the remaining odd-angle planking. It will be replaced with an engineered oriented strandboard.