It's already been about two years, but I have not finished with the rooftop garden yet. It has taken a long time because I have done a lot of research and made many reinforcements. After the last time we applied four waterproof paint layers and let it dry thoroughly, I have had several heavy rain showers, but there seems to be no water leakage.
So I put some pebbles and sand on top of the container, which is designed to hold about 150 kg per square metre, maybe more. Inside the container is a 15 cm wide steel frame supported by a 20 cm wide steel frame. The top of the container is reinforced with a 5mm thick steel plate. Four coats of paint were applied on top of that. The final result is a pile of pebbles, sand and soil about 35 cm high, and even if it rains heavily and the weight increases, it will still be about 150 kg per square metre, I guess.
My two son and I cleaned the drainage area, where leaves had made it difficult to drain the water when filming this video. It was a pool, but now the pebbles and sand have become a filter, so the drain is no longer blocked by leaves. So there will be no more pools like this ;-).
In hindsight, we should have used the PVC sheeting that creates the biogas, but we first put a felt material called geomembrane between the pebbles and the sand, on top of the waterproof paint. This is to prevent the waterproof paint from being scratched by the pebbles.
At first, we wanted to use pumice stones to create a drainage system at the bottom, but the pumice stones were more fragile than I thought. I thought it would be better to use a more solid material for the rooftop garden's long-term sustainability, so I bought a small pick-up truckload of pebbles that could be mixed with concrete, typically. It took two kids and me almost two hours to get this truckload of pebbles up to the top of the container. I used to work on construction sites, but it's been a long time since I've done so much quiet muscle work. I knew that there was a limit to how much money I could make from muscle work, and I thought about going to university. I was thinking about that in a daze of exhaustion. Even my children said that they didn't want to do this kind of work anymore. I think that was the day when I had the most faith in my words, "Then you'll have to study hard".
I think the pebbles piled up about five centimetres high. The geomembrane is spread over them. We had to put it underneath the pebbles too, so we were very close. You can't get this kind of material in a hurry, so I have to use it carefully. I do calculations, but I'm a bit of a spur-of-the-moment guy, so sometimes things like this happen. Still, I'm glad that I managed to cover all space with the materials.
I spread a thin layer of sand and called it a day. I thought that the pebbles would be lighter because of the gaps, but the sand was definitely lighter. Stones are heavy. I thought I knew this, but I was ignorant. I was quite exhausted. The next day we spread sand and then pumice stones on edge to make it drain a bit better. To be honest, I should have lined the edges with pumice before laying down the sand, but for now, it should provide drainage from the top layer of soil. In heavy rain, the water will drain from the pebbles to the sand layer, which will then drain through the geomembrane to the pebble layer at the bottom.
It will take about two more days to plant the soil and the grass. We'll take our time.