We are converting two rooms into one, which will involve raising the (concrete)  floor of one by three inches.

At the same time we will have to put in a RSJ - all of which has been agreed with Building Control.

As we are currently putting in Central Heating, it has occurred to me to run the pipes where the shallow floor joins the other, and then cover them with screed to the required depth.  A friend tells me that Building Control is likely to want these in conduit.

What  is the simplest form of conduit to use?  It would have to be fairly shallow because of the limited depth of the floor - how about 22 mm plastic pipe?  If so, what do I use on the t's to the radiators?  

Should there  ideally there be insulation on the pipes, if so how about waste pipe? Or do I really have to form a 3" trench?

Regards

John D

NB I would rather present Building Control with a reasonable fait accompli  than discuss it with them at this stage.......