Building a deck is a great way to extend the outdoor living space of a home or business. Making sure it is solid and structurally sound from the ground up though, is often a matter of 4×4 vs 6×6 deck post. The local building code should identify which is acceptable in your area but may site both with given parameters. So, which is better?
The load capacity of a 3-foot #2 grade 4×4 is 17,426 pounds, and a similar 6×6 is 20,834 pounds or 16% better. However, an 8-foot 4×4 supports 6468-pounds and 2339-pounds at 14-feet, while a 6×6 is 18032 and 10550-pounds respectively – or 64% and 78% more load capacity. So, for posts 3-feet and shorter, it’s a matter of preference, above 3-feet use 6×6.
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In this article, we’ll explain 4×4 and 6×6 posts, when and where to use them, how to secure them to a beam, and the spacing between post supports. We’ll also look at posts for deck stairs and deck railings. By the end of your read, you’ll be able to identify which post is better for your deck construction to ensure it is structurally sound and code compliant.
4×4 Deck Post6×6 Deck Post
Decks that are more than 30-inches above grade must have railings extending at least 36-inches above the deck surface. The railing or guard posts must be nominally a minimum of 4×4 and fastened perpendicular to the rim joist with (2) 1/2″ through-bolts and washers. The 4×4 should not be notched to the deck.
A 6×6 will work as a railing post too but is over-kill unless there are other aesthetic or structural reasons for the heavier posts. The 6×6 is larger and checks and cracks will be more visible, however, it may not twist or bend like a 4×4. It can be notched by up to 2-inches to sit on the deck and fasten to the rim board.
The style of railing or desired look may require a different post, but for most deck railings 4×4 posts work well. Once they are tied in with the top and bottom rails and the railing cap board attached, they’ll resist twisting and bending.
The choice of 4×4 vs 6×6 deck post depends on the local codes, deck dimensions, and aesthetics. While a 4×4 under 5-feet will do the same job essentially as a 6×6, the more solid timber resists bending and twisting much better. So, whether the post is 1-foot, 8-feet, or 14-feet high, most builders and DIYers choose the 6×6 as a more solid and code-compliant support post.
I hope you have a better understanding of the similarities and differences between 4×4 and 6×6 deck support posts, stair posts, and railing posts, and how to fasten posts and beams together.
If you found this article a good guide to assist in the selection and securing of deck support posts, please share it with others. As always, your comments and suggestions are appreciated.