Unless you want your brand-new deck sliding off of its foundation you’re going to want to use J bolts to keep things locked in place. But how do you know which size boards best for your deck?
The right J bolt anchor size is going to be influenced by the kind of material you’re building your deck from, the size of your deck, and a handful of other factors. As a general rule of thumb, though, J bolt anchors for decks, and six, eight, and twelve inch lengths.
In the rest of this detailed guide we run through (almost) everything you need to know about J bolt anchors, finding the right size for your project, and making sure that anchors are set correctly.
Let’s jump right in!
What is the Best Size J Bolt for Deck Post?
As highlighted a moment ago, finding the right size J bolt for your deck project is a little more involved than most people think – but it’s not the hardest puzzle to crack.
The idea here is to choose bolts that are long enough to really sink into the concrete (while it’s still wet), providing a rock solid base for you to attach your framing sills to. You want to be able to have at least 2 ¼ or more inches of bolt sticking out of the concrete, giving you plenty of room to slide on a sill plate and then bolt it down.
At the same, you need to consider the depth of your concrete footings and foundation that you are working with.
After all, it doesn’t make all lot of sense to choose a J bolt that is 12 inches long when you only have 10 inches – or even 8 inches – of concrete foundations/footing to work with. The bottom of your bolt would be almost sticking out of the bottom of your foundation and footing.
You’d lose all the strength and integrity that you are after.
Because the overwhelming majority of foundations and footings for decks and porches are going to get pretty deep, though, you can generally get away with anything from a 6 inch to a 12 inch bolt.
6 inch, 8 inch, and 12 inch bolts (threaded at the top for at least 2 inches) are far and away the most common pieces of hardware you’re going to find on the market today. These bolts are generally half-inch to 5/8 inch in diameter, too.
That’s more than enough “bite” for you to set your framing solidly on your foundation or footing.
How to Choose Anchor Bolts
Choosing your anchor bolts is a big piece of the puzzle.
For one thing, you need to consider the depth of the foundation and footing that you’re working with (like we highlighted a moment ago).
You’re going to want to have a little more than 2 inches of bolt sticking out of the top of your concrete work – and you’re going to want at least 4 inches (or more) of the J bolt sticking down into the concrete itself.
Secondly, you need to think about the kind of sill material that you are working with.
If you are using standard 2 x 4, 2 x 6, or 2 x 8 sill material (usually 2 x 6), that means you’re really going to have a board that is an inch and three quarters in thickness – and that’s why you want to have at least 2 inches of bolt exposed.
This will leave you plenty of room to work with when you put the washer and the nut on the bolt, tightening it down and securing the sill in place.
When in doubt, 8 inch J bolt anchors are generally going to get the job done. 6 inch J bolt anchors can be used on smaller decks that might not have as much weight bearing down on the sill plate. 12 inch J bolt anchors – or larger – should only be used in projects that are particularly “heavy duty”.
How to Set J Bolt Anchors
There are a couple of things you need to keep in mind when you are setting J bolts.
Concrete Curing
First, it’s important to remember that these bolts are going to be sunk into the concrete while it is still at least a little wet.
You need to make sure that the concrete has cured just enough to support these J bolts from sinking right down to the bottom of the footer or the foundation, but not so much that the bolts aren’t going to be able to be pushed into place and “lock-in” when the concrete fully hardens.
This can be a bit of a headache when you’re dealing with the heavier galvanized or stainless steel J bolts on the market today. You might even need to get your hands on a plastic sleeve that sort of sits on top of the concrete, holding the J bolt in place and preventing it from sinking until the concrete hardens enough.
J Bolt Location
Secondly, you definitely need to think about J bolt location throughout your foundation and your footer.
These bolts need to be implemented strategically throughout the perimeter of your foundation/footer, and they need to be done according to code. Usually this is 9 inches minimum from the end of each plate and 12 inches maximum from the same, with bolts spaced apart every 6 feet or so (depending on local code).
Finally, you want to be sure that these J bolts are as straight and plumb as possible.
Conclusion
These are huge pieces of the puzzle when building a deck – they anchor the deck structure down to the foundation itself – and you can’t afford to have anything “out of whack”. Really take the time to set these correctly and use those plastic sleeves we mentioned a moment ago to keep your J bolts from floating out of position during the cure.
At the end of the day, so long as you cover all of those bases – and pick the right size J bolt to begin with – you won’t have anything to worry about.
We hope this blog post helped you figure out all the right things about the right J bolt size. Take a look at our other most recent blog posts below:
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