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Blocking (12)

Blocking is placed in-between longer lengths of floor joists to keep them from being able to twist and roll onto their sides. The 3-D diagram above shows what we call "solid" blocking. These short lengths of board are cut from the same stock that the floor joists are made from. When you build your deck, throw the floor joist boards that have gone "wild" (badly twisted or cupped) into a separate pile. Later, cutting this crooked lumber into short blocking makes good use of boards that would otherwise have to returned or scrapped.

Another method used to keep the joists from rolling onto their sides is "X-bracing". This consists of two 1x4 boards cut to fit in an "X" pattern between the joists. You've probably seen it used on someone's home. We do not recommend using "X-bracing" since the nails used to hold the bracing almost always end up splitting the 1x4's. This fact coupled with the shrinking and swelling from outdoor use renders "X-bracing" useless.

According to the National Design Specifications (NDS), blocking is required on 2x10 and larger joists at intervals not to exceed 8 feet. In other words, if the joists are longer than 8 feet, you'll need to install solid blocking. On BestDeckSite, we recommend installing blocking on 2x8 joists too.

Here's a word of caution. As you get on a roll calling out numbers for the guy at the saw while hammering in the preceding block, make sure not to throw off the joist spacing. It's easy to do since the affects of each block that's off a little in length is cumulative. If you're going to be installing decking perpendicular to the joists, you don't want to get the joists so far out that the ends of the deck boards don't land on the center of the joists.

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