DIY Doctor UK DIY Forums

I'm looking to build a retaining wall, probably in standard concrete blocks laid flat. It will be about 7m long and minimum of 1.3m high and will be filled behind with hardcore.

The ground I think is chalk, but my questions are:-

1. Will a 9" wall be ok without piers?

2. Am I better off making the wall wider by making it a cavity, or using hollow 'H' blocks?

3. What Depth and width should the footing be?

Hi justaddwater
Laying solid concrete blocks flat will be fine but use a strong mortar mix 4 or 5 to 1. Probably worth adding a pier at either end.
You will need 18” wide foundations but the depth will depend on ground conditions - you will have to dig deep enough to reach a very firm base ie a spade will not go in very far.
Regards S

Thanks Stoneyboy.

Nice straightforward answer. I am just a bit concerned about the amount of weight on the footing with just the height of blocks on top

Hi justaddwater
In terms of the depth of the foundation itself you will need to make them at least 200mm, you could add rebar if you do not get down to a solid base.
Regards S