DIY Doctor UK DIY Forums

Hi all. I have a Victorian house with no dpc and essentially no foundations, just 5 or 6 courses of brick below floor level. The ground is heavy clay then a thin layer of sand then the floor is bricks, laid 'block paving' style with no mortar. The bricks are butted up tight to the walls. I understand that this brick floor is an important structural element which makes up something of a "foundation" by stopping any lateral movement of the walls. I recently had a sewer leak in a pipe that runs under the building and had to dig up the floor to replace a section of the sewer pipe. When I lifted the bricks many of them broke up/crumbled as they are 150yrs old and suffered damage from being wet. I now need to replace these bricks and I am thinking of lifting the whole floor to replace all the bricks. I also want to take this oppertunity to "tank" the floor and walls with membrane and install wet underfloor heating. My questions are; firstly, is it okay to lower this brick floor by 75mm to give me the space i need for ufh or will this adversely effect its function. Secondly, can i use block paving blocks for this, which are usually concrete or do i have to replace with baked clay bricks, if its okay to use blocks then can i use any concrete blocks or even just pour a concrete slab to replace the brick floor? Thanks in advance for any advice.