Floor Joist Blocking

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Floor Joist blocking, installation methods and purpose

Are you considering installing a wood frame floor system for your new home? Wondering whether it’ll be necessary to block the floor joists?

Floor joist blocking is an integral part of floor framing. It provides lateral strength for a more stable floor structure through weight distribution amongst all the floor joists. This helps to fix/ prevent bouncy squeaky floors in your home.

In this article, we discuss why. We also delve into various methods for blocking joists and compare it with bridging as an alternative floor reinforcement method that you can use instead of floor joist blocking.

What is the purpose of blocking between joists?

Blocking entails the installation of short, wooden blocks for reinforcement of floor joists. The woodblocks work to prevent the floor from bouncing by ensuring even weight distribution amongst the joists.

purpose of floor joist blocking

This means that even when someone stands on a single spot in the house, their weight will be distributed evenly in the joists underneath them- thus relieving pressure off the joist that’s directly below them. All in all- blocking provides increased lateral strength for a more stable floor structure.

Is blocking required for floor joists?

Wood blocking between joists serve to minimize joist twisting and joist movement, consequently helping prevent deck board-gapping. Therefore- despite being a labor-intensive process, you might not want to skip this part during floor framing.

And that’ not all! Depending on the state in which you reside, floor joist blocking may be a requirement under the building code. This is especially a common construction requirement if your joists are more than two inches wide and 12-inches deep.

floor joist blocking , installation and purpose

How do you install a block between floor joists?

As earlier mentioned, floor joist blocking is a labor-intensive process that calls for the use of multiple types of equipment. Some of the tools you’ll need for this project include a ladder, a tape measure, a saw, a pencil, solid wood, some nails, and a hammer. Also, don’t forget to wear the proper safety gear for construction projects, including a safety helmet, protective goggles, and hand gloves.

After assembling all the above equipment, follow the procedure detailed below to install wooden blocks between floor joists:

  1. Measure the distance between two parallel floor joists– and cut out a solid wood piece of the same length. The depth of the cut-out piece for blocking should also match that of the joists.
  2. Install the wooden block by hammering down a couple of nails on both sides to attach it to the two parallel joists.
  3. Next, repeat steps one and two above for the next two joists (and so on, until the process is complete). You’ll want to place each blocking a bit off-center from the previous one to give you ample room for hammering in your nails.

Remember, a good alternative to using nails is screws, as they provide a more secure hold. Also, you’ll want to install your floor joist blocks prior to undertaking sub-floor installation.

Joist blocking methods

Joist blocking methods or patterns are the specific ways in which blocking can be installed- with a focus on aesthetic appeal. Popular blocking patterns include:

1. Alternating

Alternating is a blocking method that gives off a symmetrical appearance, since the boards are usually kept closer together. This method eases the blocking installation process, as you can drive screws or nails through the joists to the wooden blocks, instead of using toe nailing.

2. Straight Line Blocking

This method takes lots of expertise to correctly pull off. However, the rewards usually match the effort; as it gives off the best aesthetic appearance- especially if the substructure is visible over the lower deck. Straight line blocking entails straight fastening of each wooden block to the joists only at one end, while using toe-nail fastening on the other end.

Floor joist blocking vs bridging

Some homeowners prefer bridging- also known as cross-bracing- to wooden blocking for floor reinforcement. Visually, bridging differs from wooden blocking in that dual support pieces are installed diagonally across parallel joists. For comparison, in wooden blocking, a single wooden block is usually installed perpendicular to two parallel joists.

The use of double braces in cross bracing allows for a more stable floor frame. What’s more, the X-shape formed by the diagonal placement of the support braces usually leaves more room for electrical wiring and plumbing to pass through. Remember, you need such spacing for ease of access when looking to replace your wiring systems in future. This- however- doesn’t mean that bridging is a superior floor reinforcement method to floor joist blocking; as the latter method also has its upsides.

For instance, blocking is best at ensuring the floor doesn’t become saggy, as it provides more strength and rigidity. As a results, wooden floors where the floor joists are supported using wooden blocks barely ever squeak, as there’s minimal-to-no bouncing. The table below highlights these major differences between these two floor frame reinforcement methods.  

Floor joist blocking vs bridging; differences & similarities.

Floor joist blockingBridging
A single wood block is installed perpendicular to two parallel joistsTwo support pieces are installed diagonally across two parallel joists, forming an X-shape
Better at preventing bouncy/squeaky floorsLeaves more space for electrical wiring and plumbing
Uses less lumber- hence less costlyCostlier compared to floor joist blocking

Despite these differences, there exist a few similarities between bridging and blocking. For starters, both methods are used for reinforcing floor joists, ensuring your floor structure stays stable and movement-free. What’s more, both processes are labor-intensive and take lots of attention to detail to execute correctly. For instance, while you need to ensure that the cut-out pieces of lumber are the same width and depth as the floor joists you’re looking to support; you equally need to avoid splitting the ends of your cross braces when fastening them into the floor joists.


  1. Cdn.ymaws: Wood-frame floor systems and concrete slab-on-grade floors.
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Joe McGuinty
I’ve been working with floors for over 12 years. I started as a flooring contractor, primarily in materials selection. Then, I switched careers into accounting, so my wife and I began buying, renovating, and re-selling homes on the side. You’d be surprised how much value you can add to a home simply by adding new floors.

1 thought on “Floor Joist Blocking”

  1. On a 22 ‘ span one block in center is enough and both ends are blocked with beam?
    Other joists are 21’, 18’, 14’ and 12’, do they need one blocking in center too?


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