Cross Bracing Floor Joists

By Mark J. Donovan

Floor joists commonly twist and flex under heavy load. In order to reduce the amount of floor joist twisting and flexing cross bracing is commonly employed between floor joists. Normally cross bracing is installed every 8 feet, or center span between floor joists.

Cross bracing can be comprised out of wood or metal. For wood, typically 1x4 lumber is used. It is nailed at the top and bottom edges of adjacent floor joists. It is important not to split the ends of the cross braces as this will weaken their strength. Metal cross braces are also commonly used.

Cross braces should be installed prior to installing the subfloor. By installing the floor joist cross braces before the subfloor you can ensure that the floor joists are properly spaced. This will aid in the subfloor installation effort.

If the floor joists are constructed out of treated lumber, make sure to use stainless steel nails or fasteners. Likewise if you use metal cross braces make sure they are coated in an ACQ corrosive resistant coating. Regular steel or galvanized nails and metal cross braces will corrode if placed in contact with treated lumber.