Stop a Tall Deck From Swaying With Routed-In Diagonal Straps

The Problem

A small deck close to the ground can get away with little or no dedicated lateral bracing — the posts themselves add some stiffness in that direction. A big deck 12 feet in the air is a different structure. Without something resisting side-to-side movement, the whole outer edge wiggles when people walk on it. Plenty of older decks that were framed without lateral bracing do exactly that.

Knee braces at the posts are the common fix, but they only stiffen the frame near each post. Diagonal strapping tied back to the house braces the entire diaphragm.

The Technique

This deck's layout came from an engineer: several metal straps running diagonally across the tops of the joists from the outer frame back to the house, including two that cross in an X near the middle of the span.

1. Snap chalk lines across the joist tops marking the path of each strap.
2. Rout a shallow recess along each line — deep enough that the strap sits below the top plane of the joists.
3. Lay each strap in its recess and nail it off along its full length.
4. Install the decking over the top as usual.