What Is Floor Joist Bridging

Blocking when talking about floor joists is when short wood blocks are used to fill or reinforce floor joists under floors that have a space below them.

What is floor joist bridging.

Joist bridging is used in construction with long span lumber as a load sharing device. Even if your floor already has a row of bridging running down the center you can stiffen it substantially by adding two more rows. In general those values are in the sji bridging tables in the specification. The joists immediately under the load deflect substantially before the straps are tensioned and start spreading weight to other joists.

Bridging is only designed for the lateral stability forces in the joists. Normally these systems are independent of the joist system. While it does not offer as much support or prevent joist flexing as well as solid blocking does cross bracing does have some definite benefits. Properly installed wood x bridging tightens as the joists shrink to the degree that i ve seen the bottom of the joists get a slight crook in them from the bridging.

Bridging of roof decks is also needed for wind uplift conditions where stress reversal can occur putting bottom of joists into compression lateral stability concern. The catch of course is that the bouncy floor joists must be accessible from below. Bridging ties the joists together with lumber. Cross bracing sometimes referred to as bridging is the most common type of flooring reinforcement.

Additional support for the floor joists is achieved by nailing the ends of the joists into headers. The wood used when blocking is usually made up of short defective pieces of wood that can t be used in other pieces of construction. Yet it is not uncommon to find bridging not properly installed or missing all together. Bridging allows each joist to share weight with its neighbors and can cut deflection how much the joists flex by half.

Proper bridging distributes the load on the floor to other joists and over time prevents floors from sagging and squeaking do to floor joists twisting and warping. If bridging is intended to brace other components of the structure the size and connections must be indicated on the contract documents. The most common justification of bridging in floor systems is to load share between joists especially under point loading such as foot traffic. Section r502 10 of the international residential code states that header joists can be the same size as the floor joists when the header joist span isn t greater than 4 feet but if the header joist span is more than 4 feet you ll need to double the header joist and ensure that it s capable of.