Is it normal for deck posts to have deep cracks after less than a year?

Pressure-treated 4x4 or 6x6 posts are notorious for this beacuse they arrive at the job site absolutely saturated with chemicals and water. When you buy them, they often have a moisture content upwards of 80%, and as they sit in the sun for a year, that number drops down to about 20% or less. All that moisture leaving the wood causes it to shrink rapidly, which results in the **checking** you're seeing. It looks alarming, especially when you can fit a finger in the gap, but it's almost always a cosmetic issue rather than a structural failure.

Since a deck post is primarily under compression—meaning the weight of the deck is pushing straight down on it—a vertical split doesn't really compromise its ability to hold that load. Even if the crack goes deep, the wood fibers are still oriented vertically to support the weight. The twisting you mentioned happens for the same reason; as the internal grain dries at diferent rates, the timber physically pulls itself into a spiral. It's frustrating to see on a new build, but a slightly rotated post rarely affects the safety of the structure.

If you really hate the look, you can wait untill the wood is fully seasoned—ussually about a year—and then wrap the posts in **PVC trim** or cedar boards to hide the cracks. Some people try to fill the gaps with wood filler or caulk, but I wouldn't recommend it. The wood is going to continue to expand and contract with the seasons, and most fillers will just pop out or trap moisture inside the crack, which can actually lead to rot over time. Unless you see the post actually bowing significantly or the beam above it losing its bearing surface, I wouldn't push the contractor for a replacement. Most warranty claims for checking get denied by lumber yards anyway because it's considered a natural characteristic of the material. If you ever build another deck and want to avoid this, you'd need to spring for kiln-dried after treatment (KDAT) lumber or use somthing like architectural-grade cedar, which is much more stable but significantly more expensive.

If you're tired of looking at those cracks, just grab some TimberTech Post Sleeves. I used them on my last project beacuse my 6x6s looked exactly like yours after the first summer. They slide right over the existing wood and hide all that checking perfectly. It’s a much better long-term fix than trying to fill the gaps with gunk that'll just fall out. Plus, you won't have to deal with maintenace or staining every couple of years.

Oh wow, I just joined this group beacuse I'm planning my first DIY deck and this is exactly what I was worried about! Seeing that deep checking on a brand new build whould totally freak me out too, but it's such a relief to hear it's mostly cosmetic. Since everyone is talking about the posts drying out, does anyone know if staining the wood earlier in the process helps slow down the cracking, or does that just trap the moisture inside and make it worse? I'm trying to pick out my lumber next week!

Honestly, don't sweat it. I had a 6x6 twist so bad it looked like a candy cane after the first winter. I was convinced the deck was gonna collapse, but my neighbor's a structural engineer and he just laughed. He told me as long as the bolts are still tight and it's still sitting solid on the pier, it's fine. It's just the nature of the beast with that wet lumber. If the contractor isn't worried, you shouldn't be either. Just keep an eye on the hardware to make sure nothing's shearing off, but it's probly just ugly, not dangerous.

I hear everyone saying it's just cosmetic, but have you ruled out the possibility that the posts were poor quality heartwood to begin with? Sometimes if they're cut right from the center of the log, that 'pith' makes them much more prone to that spiraling you mentioned. If it's twisting enought to pull the hardware, that's more than just a surface check. Have you put a level on it lately to see if the rotation is acutally shifting the beam sitting on top? It’s probaly fine, but I’d want to be sure the bearing surface hasn't moved.