That is brilliant, the second image is worth a thousand words, I had spent hours searching but never found an image of the product that had been (poorly) described to me let alone a sectional view like that.
My 8 veluxes were a doddle by comparison, the same principle and I knew there had to be a product available to avoid casting my own poutrelles in place.
Are you wiring this house? The reason I ask is that sometimes its possible to pass cables in the hourdis (blocks between the poutrelles)as normally they are hollow.The base of the hourdis is around 1.5cms thick ,so to check if its hollow all the way across drill a hole at each end and push a rigid tube through.It can save you a load of time to cross from side to side.Don't cut the poutrelles.
Not sure if its hollow but will check later next month when we are back there. Its getting à partial rewire it has 2 pin plugs and no earth. I made small holes in the floor to run wires into the basement and its cavity walls on the first floor. I did find plastic semi ridged pipes buried in the concrete floor that had the socket wires but they were very narrow and not sure I could have used them to feed earth cables through. They were as narrow as flexy fuel pipes in an old digger Not much wider than straws.
In general hourdis made of concrete are hollow,but this will depend on the use.There are hourdis which are solid but only 8cms in height usually around balconies so that extra weight(in concrete)can be added to work as a cantilever.
Unlikely and unless the sous sol has the same construction then highly unlikely.
The ground floor is grey blocks as is the outer wall on the first floor then as flobber pointed out on the last post. It has 5mil red brick as a cavity flobber called it by its proper name. All the internal walls are the red brick, I know now most new builds are just plasterboard and metal rails.