They do have internal support inbuilt- you just can't see it...That is very impressive, but it has a fair bit of support. I was astonished at the 9m span without any supporting framework.
That's why the insulated roof panels are so 'thick' for the longer lengths compared to the shorter ones like mums 6m or my 7m ones- all their internal framework is hidden in the insulation...
The mob that made mums actually has an 'arch' inside them for their longer spans, with a bottom tie between the ends holding them together, before the entire thing is covered with the bottom 'interior roof sheet' and filled with expanding foam- (I'll see if she still has all the paperwork as it had some diagrams of how they were constructed internally)