A 'shed on stilts', our faeces are dropped from a great height straight into huge portable plastic IBC tanks which can be shifted around underneath the superstructure and then transported by fork lift trucks, tractors etc. and used for growing specific fruit/vegetables.
Since building this structure, I have learned that most systems either use a very undersized tank for collection which needs emptying too often or no tank at all where the waste seeps into the ground and is accessible to all kinds of vermin and household pets. I myself believe that it is important to give proper attention to waste that we produce and process it in the best way possible.
Actually, this building is very much more than just a dog proof composting toilet as it also has a solar shower system, a garden tool store, dedicated rain water and grey water stores and even a communal kitchen area. The total floor area is 5.5m x 2.4m and the toilet itself is just a mere1.2m x 1.5m. For stability, the floor plan needs to be at least 2.4m x 2.4m or else it will be very susceptible to the wind and would look just plain stupid!
As far as design challenges go, the first question was: 'Would the hole in the IBC top be big enough for the waste?' I really wanted the waste properly contained in a plastic tank and really wanted to be able to screw the lid back on and maybe even collect the methane gas produced. The second question was 'How to brace the front of the stilts whilst allowing the IBCs to be able to be removed?' The structure would surely be a bit wobbly without such bracing. Third question: 'Would I need a pallet truck to move the IBCs on the concrete pad?' or 'Could I find a cheap second hand pallet truck?'. IBCs can easily be moved with pallet trucks, providing that the concrete is not too rough. Basically, an IBC is a 1,000 litre plastic tank in a steel cage on a pallet.
Part 1 of the project can be found here: https://www.instructables.com/id/The-Easy-Empty-Composting-Toilet-Project-Part-1-Gr/
No calculations were made when designing this structure and all timber sizes are based on previous experience building similar structures.
Disclaimer: Check your local building codes and/or employ an architect/engineer to calculate loads and timber sizes.
The structure is 3.8m high, 2.4m wide and 5.6m long. It has 6 main upright posts of 100 x 100 mm which are anchored to the ground by welded steel post sockets set in concrete.
The critical factors in the design and construction are: