One big difference between what we are proposing to do and a rooftop garden is that we’re going to try making our rooftop space into an integrated system, with resource exchanges between the different organisms. Yes, organisms, you read that right.

Soil and plants are heavy, as are large containers with water.  Keep in mind that weight is a prime consideration on a rooftop ecology if you don’t want it migrating to the floor below.  But if you have animals they will need room to walk about and walking space isn’t heavy at all.

We’re looking to integrate fish and small animals into our rooftop area.  But while it will be an integrated system it won’t be a closed system, or self sustaining in the absence of human intervention. If we take the people out this thing dies, for the simple reason that we’re using this system as a machine to clean up cities. We don’t want to separate people from it, we want to connect them to it. It’s a machine but it’s also an experience.

On the other hand we want to make it automatic by design to a certain extent so that the people using it can do other things and come back to it every couple of days, mostly to collect produce with a little time left over to clean up as they go. We have to find out about city ordnances in Tokyo to find out what precisely we can and cannot put up there, but what we’re looking to do (using DIY and scavenged materials) is this..

A DIY passive dew condenser collects water from the air.  Gravity then takes it to a DIY solar desalinator and a DIY biological filter. I think we need to double up on water processing because the thing will be running when the sun is not shining.

The water then flows down and into a DIY fish tank.  The fish tank has the Azolla water plant growing on the water surface so that the tank is constantly producing a little of its own fish food. It won’t add up to much but a separate pre-tank, or green portion of the tank, might allow more growing space for water plants. Azolla fixes its own nitrogen in water and can double its weight in 3 days. It’s packed full of minerals and protein.  Phosphorus is the limiting factor in growth but Korean natural farming processes detail how to produce water soluble Calcium Phospate and Phosphoric Acid from waste products.

Incidentally, a rain barrel will also be required to hold rainwater, something that needs to be on the strongest part of the roof.  The Tokyo public water supply is flouridated, so we have good reason to want to reduce its use to a minimum.

That explains how the water gets on the roof.  It doesn’t explain where the biological resources will be coming from to drive this machine. Sunshine will power it, but it will still require fuel.

The fuel will come from organic waste, kitchen scraps, waste food, fish guts, old fruit etc. Thus we’re looking for a location with a large organic waste flow.  That flow will be directed towards whichever chain of use (think chain of custody but it makes you smile) that will benefit the most processing organisms.  However if source separation is laborious it would all get thrown into one large bin with earthworms and black soldier flys.

Black soldier flies are beneficial insects despite being called flies.  They eat pretty much anything and reduce its volume by 95% in the space of hours, converting it into protein and fat. This is a good thing since the worms won’t eat most fresh food waste.

I am informed that the flies would outcompete worms for food if they were not segregated in the bin. It seems that segregation, with worms and flies succeeding each other in different parts of the bin is something which no-one has yet tried. The activity of the flies feeding heats up their compartment and keeps the worms away. Of course new food can be added to another compartment to migrate the fly larvae to another part of the bin, whereupon their previous compartment will cool down. The flies are surface feeders and the worms are not, which means you can have them in a bin which is compartmentalized on the surface but one big bin underneath the soil.  The worms do like having a go at what the flies excrete and turn it into the world’s best compost; vermicompost.

Both fly maggots and worms are food for fish and chickens.

Interestingly when the black soldier larvae has had enough to eat and wants to find somewhere to pupate it moves away from the food. Ramps in the bin take the larvae up and out of the bin, where it either gets introduced to a hungry chicken or a hungry fish. The fly/worm bed leaches organic fertilizer, which drops into the water processing system and feeds the Azolla, which feeds the chickens and fish, and other plants besides.

So that’s waste converted into insect and worms, protein and fat, which is then turned into fishmeat (and more fish), chicken (and more chickens),  eggs and Azolla. Also believe it or not there is a market for insect chitin. But that would only be the beginning of course. A lot of waste means a lot of nutrients to filter out.

Having done one corner, we need to consider the rest of the roofspace. Of course we’ll need space for the chickens (or guinea fowl) to walk around. They will require vegetables, Azolla certainly, but also other roof plants. They will also require protein and fat (which the larvae and worms provide).

Now some of this will be heavy so we have to get inventive with the growing space. Thankfully there are DIY systems which allow plants to be grown on walls (I kid you not). There are also  Self Irrigated Planters  (SIPs), basically a plant pot with a water reservoir (attaches to plumbing) and an air space at the bottom.  The plant always has access to water, and some minerals (thanks to the worm/fly bin) and so grows like crazy.

What we don’t want to do is to put down a moisture barrier on the roof surface. That costs an absolute fortune. No, we want everything on the roof to be within its own moisture barrier. We want it all connected with plastic pipe. We want it cheap and efficient, hugely beneficial from the get go, whether in terms of return on investment, biodiversity created, problems solved or whatever.

What else can you have on a roof besides a fish tank, a worm bin, a bsf bin, a dew collector, SIPs and wall planters? Well you can have a trellis and a net down one side of the building for a vine. You can have a beehive too. Throw in some permaculture, perennial vegetables and herbs, some fungi and some algae and you have something pretty neat I think. It won’t look like a ornamental garden, more like a science experiment, and it won’t get out of hand weight wise because it’s going to get grazed hard.

It will solve multiple problems whilst simultaneously creating multiple benefits; for people, for biodiversity, for preventing climate change, for food security, for self sufficiency. Geoff Lawson, the Permaculturist, says that you can solve all the world’s problems in a garden. We propose to have our gardens in the middle of the city on every rooftop we can get access to.


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