What Is Floor Joist Bridging

Bridging ties the joists together with lumber.

What is floor joist bridging.

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. The most common justification of bridging in floor systems is to load share between joists especially under point loading such as foot traffic. Yet it is not uncommon to find bridging not properly installed or missing all together. Additional support for the floor joists is achieved by nailing the ends of the joists into headers.

Bridging is only designed for the lateral stability forces in the joists. Even if your floor already has a row of bridging running down the center you can stiffen it substantially by adding two more rows. Normally these systems are independent of the joist system. 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.

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. 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. Bridging allows each joist to share weight with its neighbors and can cut deflection how much the joists flex by half. Floor joist bridging is critical to the structural strength of a floor as shown in figure 1.

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. 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. Joist bridging is used in construction with long span lumber as a load sharing device. 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.

Cross bracing sometimes referred to as bridging is the most common type of flooring reinforcement. The joists immediately under the load deflect substantially before the straps are tensioned and start spreading weight to other joists. The catch of course is that the bouncy floor joists must be accessible from below. I joists are joists built with structural integrity however they still benefit from bridging which also helps reduce vibrations in the flooring.