Is it safe to put a hot tub on a deck with 5-inch screws instead of notched posts?

That deck is absolutely not ready for a hot tub, and honestly, it’s barely framed correctly for standard foot traffic. The biggest red flag is using screws in withdrawal to hold up those 2x12 headers. Screws are great for lateral movement, but they have very little **shear strength** when you're asking them to hold up thousands of pounds of water, wood, and people. Without notching those 4x6 posts or using thru-bolts with meaty washers, you're relying entirely on the metal threads of those TimberTech screws to not snap or pull out of the grain. Adding a hot tub adds about 5,000 pounds to a relatively small footprint. If he doesn't want to notch the posts now, he needs to at least install **post caps** or bolt some jack studs (short 4x4s) directly under the headers to transfer that load down to the footings. Right now, all that weight is just hanging on a few thin pieces of metal. It's a textbook recipe for a catastrophic shear failure where the whole deck just drops six inches in a split second. The 12-foot spans between posts are also way too wide for 2x8 joists, expecially if they're sitting on top of the headers without being blocked. When he says they are "shaking hands," he means they are lapped over the beam rather than being butt-jointed. While lapping is common, it doesn't fix the fact that 2x8s will bounce like a trampoline over a 12-foot span. If he puts a tub on that, the joists will likely deflect past thier breaking point or cause the decking to warp and pop screws. He needs to double up the joists under the tub area and add mid-span blocking to keep everthing from twisting. And those joist hangers he mentioned aren't optional; they're the only thing that's going to keep the frame from racking. I'd strongly suggest talking him out of the tub til he beefs up the substructure. A "fixer-upper" shouldn't include a structural collapse.

Wow, I'm totally new to this but 5,000 pounds sounds terrifying for just some screws to hold up. I don't know much about framing, but what exactly is 'shear strength'? Is that different from how much weight a screw can hold if you're just pulling on it? I'm curious if adding those jack studs you mentioned is something a beginner could do easily, or does he have to take the whole thing apart now? Also, if the 12-foot span is too wide, could he just dig and add an extra post in the middle to help, or is it too late for that?

If your dad is refusing to notch the posts, you need to convince him to swap those screws out for Simpson Strong-Tie SDWS Structural Wood screws. They have way higher shear strength than standard deck screws and are actualy designed for structural loads like headers. I’ve seen basic fasteners snap under pressure beacuse they aren't meant to carry that kind of weight. While he's at it, he shold grab some Simpson Strong-Tie DTT2Z Tension Ties to help with the racking. It’s alot cheaper than a broken hot tub, and it'll actually give you some peace of mind when you're sitting in the water.

I tried a similar shortcut on a porch build years ago and the bounce was unbearable. Tell your dad to get some 2x10s and sister them up against those 2x8 joists in the tub area. It's the only way I got my deck to stop feeling like a diving board. Also, those 12-foot spans are asking for trouble; I ended up having to dig two extra footings and throw in mid-span posts becasue the sag was visible after just one season. It’s way easier to overbuild it now while the boards are off than to try and jack up a sinking tub later.

While the previous commenters have quite rightly addressed the egregious lack of mechanical bearing for the headers, I find the mention of buried 4x6 posts particularly distressing from a long-term structural integrity standpoint. If those posts are truly 'buried deep' rather than being secured to elevated pier blocks with proper standoff bases, you are looking at an inevitable subterranean rot scenario that will compromise the entire assembly's axial load capacity long before the hot tub even reaches its maximum hydrostatic pressure. Furthermore, 'shaking hands' implies a lapped joint that lacks a proper tension tie, wich, when combined with a twelve-foot span on 2x8 lumber, fails to meet even the most liberal interpretation of the American Wood Council's span tables for residential deck loads.