JK wrote:

Toby wrote:

It is, but sadly any soil in the area is topped with a thick layer
of concrete right up to the edge of the house.

Cut back concrete along the wall, dig trench, fill to brim with coarse
gravel.


This doesn't sound like a diy job. Not if you mean the application of one
of those terrifying massive grinders that pavement operatives use in busy
shopping centres to cut curbstones!


These are hirable and rather fun.

How wide does such a trench need to be
anyway?


depends on what teh surface is, if clay, quie big - maybe half a meter wide.