Green terraces in apartments: how do you build them without the roof collapsing?

It's not like the roof is going to collapse just because of a green terrace, but you do need to think carefully about weight and structure before diving in. The important thing is to know what your building can handle and work with that, not against it.

First, check with the building management or the building's architect, because they know how much weight the slab can support. If they give you the green light, you'll need a good drainage system (that's what protects it most from damage), a real waterproofing membrane, and distribute the weight intelligently. Don't pile everything in one corner; large planters and substrate spread out better if you scatter them across the whole terrace. Some people use modular systems that weigh less than regular soil.

On my apartment terrace I tried big plastic containers instead of super heavy clay pots, and the difference is crazy 😅 Plus lightweight substrates (a mix of perlite, coco, compost) take up way less space than regular soil. And then check if your terrace has a natural slope; if it doesn't, set up a simple drainage system with gravel on the bottom before you add the substrate. If water pools up, that's what actually damages the structure in the long run. With these details you're going to have a green terrace without any risks, seriously.

Have you already checked your apartment's structural plans or talked to management? What nobody mentions is that beyond the weight itself, drainage is what kills these projects: if you don't get the irrigation water out properly, it seeps between layers and ends up rotting the slab from the inside, invisible until it's too late. You need a decent waterproof barrier, a drainage system that actually works, and yeah, confirm with engineering what extra load your structure can handle before you put a single kilo of substrate on it.