How much X-bracing is needed in floor joists

Q: I took your advice to inspect my crawl space. I noticed two small boards between each floor joist that are just hanging by a nail, crossed. Should I nail them?

A: Not all floor joists require the X-bracing you described, but you should nail the loose bracing to the joists to take some of the bounce out of your floors. When weight is added to the floors above, the joists tend to deflect or bend slightly. Secure the boards to the bottom sides of the joists using one or two 8-penny nails on each board.

When the X boards are secured, the weight applied to the floor is deflected from the side of one joist to the side of the next joist and so on and so on.

What I think has happened to your house is that the carpenter set the X-bracing before the subflooring was installed and had every intention of completing the bracing once the home was under roof. Sometimes minor things that are out of sight are out of mind and are left incomplete.

You could make it a rainy day project and at the same time check your crawl space for potential leaks.