Retainer Wall Foundation depth

L

lemeister

Registered User
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I have to build a small retainer wall in my garden for a split level lawn and the wall will at very most be 16 inches high. How deep/wide would the foundations for this wall need to be? I’m planning to use 4’ solids on the flat to build the wall.
 
Standard domestic walls have foundations which are 3 times the width of the wall and the depth is equivalent to the width of the wall - i.e. for a standard wall 900mmx300mm.

However the issue for retaining wall is different - in particular what your concern is is with lateral forces being placed on the wall. The depth of the foundation isn't the only concern.

I am not certain of the width of the foundation required - but I would not rely necessarily on the above advice by Ozzy, without further information which would back it up.
 
The wall is only 4 blocks high. I will probably get shot down here but i dont think any major technical designs are needed. If the wall is laid on some leanmix ( say 600mm wide and 300mm deep) and block reinforcement laid on the horizontal joints it should be fairly secure. Unless there is some heavy traffic on the higher level there sould be any any great lateral force. Depending on the lenght of the wall you may need to incorporate a few piers for strenght
 
At only 16 ins (400mm) I would suggest a 20N mix conc. foundation of 600mm wide x 250 mm deep (24" x 10"). At the wall height stated there will be very little lateral pressure bearing on the wall and it is not carrying any superimposed loading so you should be fine.

I would suggest using a fairly strong mortar for bedding the blocks
 
As an ex-bricklayer I don't think anything like a 10" depth of concrete is needed for a 16" high wall, especially if it is built with 4" blocks laid flat. At most I would put 4" of lean mix under it at 18" wide.
 
BillK said:
As an ex-bricklayer
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Is that why you are an ex brickie because you always used 4" concrete for a foundation

Just joking mate.

To be honest if anyone intended to use 4" concrete as a foundation they may as well lay a course of 10N concrete blocks flat on the ground
 
As long as the blocks are laid at right angls to the wall then fine.

I'm an ex bricklayer by the way as I, eventually, found a better job as Human Resources Director of a company employing 5000 people.
 
Big shift there in employment styles.

I suppose we could say that you are now throwing the thick bricks out instead of throwing them up
 
Big shift that took me 29 years and a lot of hard work to achieve, but which eventually meant I was able to retire at 55.
 
BillK said:
Big shift that took me 29 years and a lot of hard work to achieve, but which eventually meant I was able to retire at 55.
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And yet you still have a great sense of humour after all that work!

nutty, that does seem like a lot of foundation for such a small wall, what calculation do you use to work that out?

B.
 
bankrupt said:
nutty, that does seem like a lot of foundation for such a small wall, what calculation do you use to work that out?

B.
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Wall will be 215 wide so 215 x 3 = 675. If using a digger - 600mm wide bucket then 600mm trench.

Depth = wall width = 215mm

now that may seem slightly excessive and I would normally say a 450 x 150 foundation would suffice. However having seen quite a few people build these walls up higher at a later date (for garages, sheds, screen walls etc) then I would always reccommend the wider found. Very little extra cost at the time
 
BillK said:
As an ex-bricklayer I don't think anything like a 10" depth of concrete is needed for a 16" high wall, especially if it is built with 4" blocks laid flat. At most I would put 4" of lean mix under it at 18" wide.
Click to expand...
I'd second that, the wall is only the hight of a chair
 
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