Hello. What an amazing website!
I'm planning to build a step from the back door of our house down around 300mm to the garden level. The design is very much like the graphic on this page: http://www.pavingexpert.com/featur01.htm#door - 2 levels with 3 flags on each.
Reading that page I'm a bit unsure about whether I should be filling in the space. The part about damp proof course suggests that a hollow step will negate any DPC concerns, but the part about secure fixing of treads, suggests that if you have an overhang you must fix the slab to the main structure and so must fill it in.
Using 600mm square flags and 220mm bricks I'm expecting an overhang of ~30mm.
Does that mean I should fill it in and use some sort of drainage barrier? I'm trying to keep material costs as low as possible so if there are worthwhile alternatives, I'd be interested to hear them.
Thanks