One of the key features of earthship is their use of waste materials in construction such as tires, bottles, cans etc. In the Waiheke earthship we are going to use bottles as underfloor insulation. We haven’t heard of any other earthships doing this, however it fits into the whole earthship ethos so I’m surprised that its not part of Mike Reynolds approach. The bottles will be laid on their side in a bed of sand over the damp proof membrane. Another layer of sand will cover the bottles and the spaces between them, and then a concrete pad poured over the top. On top of this we are going to have an earth floor for a more giving and comfortable feeling underfoot than a hard concrete finish.
According to our architect Graeme North, preliminary calculated R values for 100mm thick concrete floors insulated underneath with bottles laid in dense sand is approx. 1.65 m2oC/W and with bottles laid in pumice sand is approx. 2.06 m2oC/W.
This ignores the R value of the earth underneath the slab which varies according to floor perimeter length and with any edge insulation.
These figures have not been fully checked, and are calculated first order assumptions only, with considerable margin for error. The actual insulation values can only be proved by testing.