Building a retaining wall next to house wall.

[Adam]

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?

Thanks in advance - Adam...

[stuart noble]

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.

[Adam]

"stuart noble" inch or so clearance behind, and random distances between them. A single

Thanks for the response, Stuart. It sounds like I've totally over-engineered it from the description of your retaining wall; ours probably isn't going to be much higher.

In the end (as your response hadn't appeared by the time I started work) I shuttered the first ~120mm of the trench nearest the house wall, laid rubble, then gravel, then sand in the bottom (to a depth of about 150mm), then laid a 150mm deep concrete footing with the rods from the iron fence supporting it and exposed by about 200mm out of the top. I plan to fill the 120mm shuttered gap with gravel when the shuttering comes out. Hopefully that will be plenty strong enough and will drain well...

Cheers - Adam.

[stuart noble]

I think so. As it isn't very high, and isn't going to take any weight, the only thing you have to think about is the soil. Ours is pretty sandy, but a clay soil can exert a lot of pressure when it freezes. I left a gap here and there in the mortar on the bottom course for drainage. I wish I'd left a few more to grow trailing plants from. Lavender's pretty good for hiding the brickwork.