Raised beds

Hi TG, the foundation depth will depend on your soil conditions, you want to go down at least one block depth (250mm) - basically you want to get past the organic soil level so the foundations sit on top of the subsoil. If your soil type is clay or sand you may need to go a little deeper. I assume you will use 100mm wide blocks, these will be OK up to 4 rows high as a single skin, you could bang in some rebar into the inside of the corners to provide more stability. There is a limit on length of run of a single skin wall before you need to use pillars, I can't remember offhand what that is, I'm sure for a small run like a raised bed - say 10ft long you won't need pillars.

It will pay to line the inner side with plastic to prevent moisture being drawn out of the blocks, also it stops the block wall from getting damp and will help stop the frost getting behind the render and blowing it off. Make sure that the render stops 3 or 4 inches above the soil level (you need exterior grade 'stop beading' along the bottom, which allows the water to drip off the render without getting into the wall). It would be best to have a weatherproof wall topping (coping stones) to throw off water, but most people don't bother with this and may look a little odd on raised beds.

Good luck - and let us know how it goes. :thumb:

 

It sounds sensible to add seepage holes. I'm not sure what else you can do about the stop beading, its not essential as it is really intended for house walls that have a damp proof course. Garden walls of this size rarely have a damp proof added. The danger of taking the render down to the ground level is that it will draw moisture up all the time (but so will the concrete blocks anyway) so its not a great risk rendering as close to the ground level as possible.

7m is quite a long run and in my opinion would be unstable, 2 or 3 piers would help along with the reinforced corners.