Is it normal for a second-story deck to feel a bit shaky during a party?

That swaying is almost always caused by a lack of lateral bracing, which is common when you're dealing with tall posts. When you have people moving around on a second story, they're creating horizontal force that those vertical posts just aren't designed to resist on thier own. You basially have a giant table with long legs, and any shift in weight is going to make the whole thing rack.

You need to install **diagonal bracing** between your posts and the main beam. Ideally, you want 4x4 or 2x6 braces at a 45-degree angle that tie the post to the beam. If the posts are relly tall, you shold also look at X-bracing between the two posts themselves. This triangulates the structure and stops that side-to-side movement. Without it, you're putting a massive amount of stress on the bolts at the ledger board, which isn't a great long-term situation. For the bounce or vertical vibration, that usally comes down to the joist span or a lack of **mid-span blocking**. If your joists are running long distances without a row of solid blocking down the middle, they’re going to flex every time someone takes a step. Adding a row or two of blocking stiffens the whole floor system by forcing the joists to work togehter instead of individually. Check your stair stringers while you're at it. If they feel sketchy, they might be over-spanned or not tied into a solid landing at the bottom. Tying the stringers into a concrete pad or a buried landing helps alot with that springy feeling when people are carrying heavy trays. And it’s much easier to bolt these reinforcements in now than to wait for the connections to work themselves loose after a few more parties.

Spot on about the bracing. People realy underestimate how much those tall posts want to pivot under a crowd. One small thing to check alongside those diagonal braces is your lateral load connectors at the house. If you just have standard bolts in the ledger, adding some DTT2Z-style tension ties to the house floor joists makes a world of difference. It stops that subtle 'pulling away' sensation that contributes to the sway on elevated builds. Even with solid posts, if the house connection has any tiny bit of play, you'll feel that movement every time someone shifts thier weight.

Seen this dance before. Everyone’s talking braces, but did you notch those posts? If your beam is just bolted to the side of the posts, you're asking for trouble. Back when we built 'em to last, we’d always notch a 6x6 so the beam sits on a solid shoulder. Relying on bolt shear alone is why you’re feeling that wiggle; those bolts will eventually wallow out the wood holes. If you didn't notch, look into some heavy-duty post caps. It’s alot better than the old 'bolt and pray' method we saw back in the 80s.

Oh man, a two-story build sounds absolutely incredible! I'm just starting to plan my very first platform deck and I'm so hyped to get some wood delivered. That cornhole tournament idea is genius for a housewarming party! Since you mentioned the string lights, did you have to run a dedicated outdoor circuit for all that or just use an existing outlet? I'm worried about blowing a fuse if I go overboard with the vibes on my setup! Also, has anyone ever used those fancy black decorative metal plates for bracing instead of just wood? They look so sharp but I wasn't sure if they acutally help with the wiggle.

Quick update—I added some diagonal bracing between the posts and it defintely cut down on that side-to-side sway. It feels much more rigid now! I’m still getting a bit of a vertical bounce near the stairs though. I realized I didn’t notch my 6x6 posts like suggested. whould those DTT2Z tension ties help with that, or is the beam connection the real culprit?