How to Build a Hot Compost Bin.

Latest Update 17th July 2017.

This is my homemade hot compost bin.  Its purpose is to make relatively small batches of compost using high temperature microbial breakdown.

The unit's external dimensions are 950 x 950 x 1070mm (lid and floor included) and it's assembled from 4 identical wall panels plus 2 identical top and bottom panels.
Recycled timber is used to make a simple exterior frame for each wall panel, and 2 layers of 60mm rigid polystyrene foam are glued together to make a single 120mm thick panel which is then bonded into position within the frame.  Each wall panel is 830mm x 830mm x 120mm (thick).

Once the glue is set, both sides of the wall are covered with heavy duty shadecloth stapled to the timber frame to protect the foam from damage.
Each sub-assembly is made by joined 2 panels together overlapping them at their corners.  They are joined top and bottom using galvanised angle brackets on the inside and galvanised flat joining plates on the outside.
Two saddle clamps are screwed into position as shown.  They help to handle the sub-assemblies when they are being separated so the compost heap can be aerated.
When the two halves are brought together, they are secured using small cabin hooks as shown above.
The lid and floor are made from 60mm polystyrene foam and 75% shadecloth. Two layers of the foam are laminated together using "no more nails" glue and covered with the shadecloth to improve impact resistance and add a bit of UV protection. 

Two pieces of shadecloth are cut and glued to the outside of the foam block, overlapping at the sides, so they are double the thickness of the top and bottom.

The top piece hangs down past the bottom of the lid on 2 sides so it can be hooked onto the base using 35mm gal bullet head nails as hooking point. 

Both of these components are 950mm x 950mm x 120mm.  Their different colours are not important (they were determined by the availability of scrap shadecloth from my shed).
There are 4 of these hooking points holding the lid in position so it wont blow away in windy conditions.  Removing and fitting the lid is very easy, and its light enough for even an old man like me to handle.  The floor is held in position by the weight of the other components.

This picture shows the bin just finishing a 300litre batch of hot compost which took 12 days to make in mid winter.  It ran a little too hot at 70C for the first 4 days, but after adding a little straw mulch it dropped to 65C and stayed there for 8 days until it dropped overnight to 40C on the 12th day.