EPS raft foundations with one trench containing a steel post first?

[low_and_there]

Following some of the reading on this site, we're interested in using the insulated raft foundation approach for our extension. Our SE denies all knowledge of insulation and wants nothing to do with it so I am looking at getting one of the providers to do the design work.

 

Trouble is this is for an extension and in order to knock out the wall in question, to then do the dig and lay the raft, we first need to support the floor above, which means we first need to put one steel post in the ground - this will have to therefore be done using a trench foundation rather than sitting on the raft itself.

 

To do this then, how do we best insulate that steel post so it doesn't create a big thermal bridge? Is it simply a case of lining it with EPS from the base? Or using something like an Armatherm thermal break at the base... Any suggestions?

 

thanks

[Temp]

I think I would want that post resting on the existing foundations if possible in case there is any movement of the new relative to the old. But perhaps I worry unnecessarily