Adam wrote in message . ..
Hi All,

Time to test your expertise again...

We're doing a lot of work in the (very small) garden in our colonies
property in Edinburgh. Polly wants to have a raised bed next to the
house wall (it's actually the wall of our downstairs neighbour,
despite this being our garden), but we can't actually stack soil up
against the wall as this will traverse the damp course. The plan is to
build a wall about 20cm away from the house wall to retain the raised
bed - probably about 50-60cm high - and have gravel in the gap.

We've dug a trench for the footing and about to lay the concrete and
some reinforcing rods (salvaged from an old iron fence). The trench is
about 40cm deep and 50cm wide by about 5.6m long (almost the width of
the garden) and is dug down directly next to the house wall. I was
planning to lay the concrete footing directly against the house wall,
because I assumed this would add stability. I'm not so sure this is a
good idea now, for a couple of reasons: the need to add an expansion
joint between the footings and the house wall and the need to put a
fall into the concrete's upper surface away from the wall.

Should I have some soil between the house wall and the footing?
Something else, perhaps, and if so, what? Any other advice?

I've seen this done with a series of four sided brick troughs, leaving an
inch or so clearance behind, and random distances between them. A single
structure may be vulnerable to frost expansion, especially if the soil is
heavy. I can't see that you'd need an expansion joint between the house wall
and the footings over a 50cm span, or a fall for that matter. There isn't
going to be surface water running towards the house.
I have a raised bed over a similar length, but only 3 bricks high, so it has
no footings other than a 4th brick underground. Works really well and saves
the old back a bit.