Is it normal for thick decking to have a bit of flex with 2000mm beam spacing?

The springiness you're feeling comes down to the span of your 48x148mm joists. At a 2-meter gap between beams, those joists are pushing their structural limit for stiffness, even if they aren't anywhere near breaking. While a 148mm joist can technically handle that distance, the 'bounce' is a classic symptom of choosing a shallower timber profile over a longer span. Those heavy 33x170mm boards add a lot of dead weight too, which actualy increases the deflection you feel underfoot. Since the decking is alredy down, you have a couple of options that don't involve ripping the whole thing apart. The easiest fix is to install **noggings** or blocking between the joists. If you can get underneath, screw in short lengths of the 48x148mm timber in a staggered line down the center of that 2-meter span. This ties the joists together so when you step on one, the load is shared across three or four others. It won't stop the wood from flexing entirely, but it significantly kills the vibration.

If you have access to the underside and blocking doesn't do the trick, you could also 'sister' the joists by bolting another 48x148 alongside the ones in the bouncier sections. But honestly, even just adding a single row of solid blocking ussually firms up a 50 sqm area enough that you won't notice the movement anymore.

Next time, it's usually better to go with 48x198mm for anything over 1.5 meters if you want it to feel like a concrete floor. For now, just focus on stiffening that mid-point of the span. It’s a common trade-off when trying to keep the deck profile low to the ground, but it's definitely fixable without spending another 4000 euros.

This sounds like an absolute massive project, 50 sqm is huge! I'm just starting to plan my first small landing and I'm getting so pumped seeing everyone's builds. The idea of anchoring to bedrock sounds hardcore. Since you mentioned the dimple board and drainage, did you have to deal with any weird slope issues? I'm curious because my yard is basically a hill and I'm worried about the posts looking uneven.

Spot on about the 148s being a bit thin for a 2-meter span. One thing I'd add is when you go in to install those noggings, make sure you're using proper structural screws or even 90mm nails rather than just standard deck screws. Those heavy 33x170 boards put a ton of shear stress on the frame. If the blocks aren't super tight and fastened with somethig beefy, they’ll eventually start rubbing and you'll trade that springiness for a loud squeak every time you walk across it. Checking the rim joist connections while you’re under there wouldn’t hurt either.

Quick update—I added some noggings with structural screws like you guys suggested, and it definitly stiffened things up a bit. However, that slight bounce in the center of the 2-meter span is still there. Since the boards are allready down, do you think adding a mid-beam underneath without removing the decking is doable, or am I stuck with the spring?