Just a heads up guys, here is a supplier of insulated slabs similar to Creagh's Spantherm
http://www.nu-span.com/index.html
I've no affiliation, just came across them through work.
It's something similar to the link below. I have an oil boiler located in my detached garage. This prevents me from heating my back yard
http://www.treco.co.uk/products/boiler/Uponor-Pre-Insulated-Underground-Pipe