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Easy Blocking for Wood I-Joists

Adding plywood gussets to short lengths of I-joist makes for easy-to-install blocking in an engineered floor frame

January 16, 2019
wooden i-joist jobsite know how pro remodeler

Engineered I-joists can span long distances to make a flat and solid subfloor. Tying the joists together with blocking makes the floor even stronger and stiffer. So one of the last things that need to be done before sheathing the deck is to fill in with blocking.

Making “Professional” Blocks

To make the blocks, I cut sections of I-joist 1½ inches smaller than the space between the joists, then nail a scrap of ¾-inch subfloor material to each end of the block [1]. This creates two large nailing fins.

Calvin Cutts works from a ladder to install the blocks. After lining up each block with the tops of the floor joists, he nails it in place, top and bottom, on both sides [2].

The subfloor strips are about ½ inch shorter than the full height of the I-joist [3] so that the nailing fins will not stick above the tops of the joists and cause humps in the floor. 

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About the Author

About the Author

David Joyce owns Synergy Construction in Lancaster, Mass. This article is adapted from a video at Thanks to David and his crew for  allowing us to hang out at their jobsite.



Why not use "X" metal bridging, wouldn't it be less time consuming and you're not relying on extra I-Joists to do the task?

Well, I hope there is some!

I can't seem to find the live load of an EXISTING beam consisting of TWO 2X6's blocked 3.5" apart every 24", for a 14 foot span. A total of 7ea. 3.5" blocks.
Can you guestimate a live load, say 30% accuracy...ish

For a remodel and lacking access to I joists to cut for blocking, can I simply fasten 2x lumber to plywood/OSB and make these? It will be missing the center 'webbing'. Thanks!

Same issue here? What do you do to sister or block with ijoist instead
Of traditional dimensional lumber??

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