In the last few weeks, our inspectors have noticed a few situations – mostly with do-it-yourself homeowners – where people have used screws rather than nails for structural work - that is, securing joists, roof rafters and the like.
There’s a huge difference between the two, and in most cases, it’s important to use nails for structural building (that is, assembling load-bearing walls), not screws.
Screws are amazing at securing one chunk of wood to another when the forces are in line with the screw. So they're pretty darn good at holding sheathing down onto a floor system, or roof truss. But they're not so good at holding things together when shear forces (those perpendicular to the line of the screw) are involved.
Nails, however, are best at securing one chunk of wood to another when the forces are perpendicular to the line of the nail.
In most cases, screws should not be used for any kind of structural construction.