The upgradeable Blair VIP (uBVIP) - SuSanA

The slab extension
Many types of superstructures can be build on or around the
slab. The spiral door-less version has the least maintenance
problems. But toilets with self closing doors can also be built
using rubber hinges. In both cases an extension to the slab on
one side can be made and the walls of the toilet built on the
slab and extension.
Slab extensions made for spiral structure
(grass and brick)