I've had to remove a few T&G floorboards near some walls to replace
rotten joists in a cavity brick house. In order to get underneath the
boards I had to dig out about 6-8 inches of rubble (bricks, mortar and
clay soil) making a space of about 1'4" so I could crawl around. Having
replaced the rotten joists (and fixed the drainage problems that caused
them) I don't know whether to return the rubble, replace with a cleaner
& easier draining (and less smelly!) fill like crushed rock or leave it
cleared. The ground level underneath the house is now about 5" lower
than that outside the house.

Any suggestions would be appreciated.