Under it was a shallow wooden tray built between the floor joists.
That's so the load-bearing wall can run right down the middle of the house and hold the floor joists for the second story.
In an unfinished basement, it's easy to use the space between the floor joists for storage.
That one time you were trying to take that floor joist.
Underneath, beside the floor joist, there is a long, narrow space.
No sooner had his head descended below the floor joists than the door was slammed down above him.
This is an old method, used at the time when floor joists were stronger.
Try to position the nails so that they enter the floor joists, but this is not essential.
In the attic, it's best to secure it to the floor joists.
The ceiling has a central spine beam and floor joists.