Deck Blocking and Bridging

A deck should provide a sturdy foundation for outside activities as an extension of the living room. A shaky or bouncy deck design is reason for concern and undermines faith in the builder's abilities. Deck joist blocking is a straightforward solution that promotes a more solid structure.


The building code requires blocking at the open end between joists to prevent rotation or at 8-foot maximums if the joists are larger than 2x12 in size. The majority of builders, however, know that blocking every 4 to 6 feet unifies and strengthens the frame.

In this article, we will explain what joist blocking is and why it is important, as well as the necessary requirements, procedures, and spacing. In addition, we will describe other methods for installing blocking for various goals. The article contains all the information necessary for blocking deck joists.


What is Joist Blocking in Deck Construction?

Deck joist blocking is a piece of wood cut from a joist and put between two joists to connect them or bridge the space between them. Most of the time, the blocks are all the same length. They are 14-1/2" for joists that are 16" apart, 10-1/2" for joists that are 12" apart, and 22-1/2" for joists that are 24" apart.


In 2018, Section 502.7 of the International Building Code (IRC) says that the ends of deck joists must be blocked with 2-by material that is the same depth as the joists. This is done to stop the joists from turning. You can also use a band or rim joist, or a header, instead of end blocking. In Section 502.7.1 of the IRC, it says that joists that are bigger than 212 must be blocked every 8 feet.


Read more: How to Build an Octagon Deck


There are many ways to connect joists so that they move less side to side. Strapping is when you put a 13 board or bigger across the bottom of the joists every 4 to 6 feet from one outside joist to the next. Each joist has a strap attached to the bottom of it. The straps hold the distance apart and stop the joists from turning or bending too much. They are easy to put in while building or after. But because they are flat, they tend to hold dirt, water, and nests, and they rot out quickly.


Blocking is made of short pieces of solid joist material that are cut into blocks and put between joists. Even though they aren't as fast or easy to install as strapping, they offer much more structural support. During construction, they are often put in an alternating or straight line between joists. When a deck is put on top of them, they are hidden. The thin vertical profile also makes it better at getting rid of water and makes it last longer.


Cross bracing deck joists is done by cutting each end of a 22 into a 45-degree angle and fastening it between the joists. Cross bracing joists is better than strapping or blocking for spreading the top load from one joist to the bottom of adjacent joists when the joists bend, but blocking is almost as good. Cutting and installing cross joist braces takes time and extra materials, and the ends often break when they are fastened, so they have to be replaced. Predrilling is helpful but takes longer.


Most deck builders cut up scrap or unusable joist boards into blocks that they put in the middle of the deck or every 8 feet between beams. Blocking is also often used to make a frame or racetrack to support deck board designs like picture frames, herringbone, zipper, parquet, and diamond. Also, blocking provides joist braces that hold up posts for railings, stairs, and other structures.


Pro Tip: If you use pressure-treated wood, remember to paint any cuts or drill holes that expose untreated wood. This will stop the wood from rotting. Also, you should know that chemicals used to preserve wood corrode metal that is not protected, so use fasteners that are made for treated wood.


Deck Joist Blocking Methods

Putting a joist brace between two parallel boards helps stiffen the frame and move weight from one member to another. When it comes to putting up blocks, builders often have a preference based on their experience, the cost of materials and labor, how well it looks, and whether or not it meets building codes. The most common ways to block joists are listed below.


Solid Blocking to the Full Depth

Using blocks made of the same material as the joists makes sure that the sizes are the same and that the joists are fully supported from the top to the bottom. It is also a good way to save money on joist scraps and twisted or bowed joist timbers that can't be used for anything else.


The Diagonal Cross Bracing

For diagonal bracing, you need to use 22 pieces with each end cut at an angle. Two pieces are used to make an X between all the joists to transfer loads and deflections from the top and bottom. Cross-bracing deck joists takes more time and materials to cut and put in place. Also, the ends often break when they are put in place, so you have to use a new piece. Predrilling solves the problem of splitting, but it costs more and takes more time to install.



Switching the blocks between joists is an easy way to make sure they are solid. Measure where the blocks need to go at both ends of the deck and snap a chalk line. If you put blocks on either side of the line from joist to joist, it's easier to direct fasten than if you came in from above or below. Many people who build decks will measure so that the line of spaced-out blocks falls under a deck board. This keeps the blocks dry and hides them from view.


Straight Line

Straight-line blocking also uses a chalk line for the layout, but all of the blocks are on the same side of the line. One end of the blocks can be attached directly to the layout, while the other end must be toe-nailed into place. From above, the straight line of joist bridging is easy to hide under a deck board, but it looks better from below.

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