Trench foundation width

[DannyG]

Hi all

 

Our proposed build has 400mm wide masonry walls (200mm cavity) but I've just received the plans back from our structural engineer and he's specified just 450mm wide foundations in some places. This seems like a very tight tolerance to me and would need to be dug very accurately, is this normal? I was expecting 700mm all round.

 

We're on clay down as far as we checked (15m).

 

Thanks

Dan

[George]

There is a minimum of 50mm on each side (so wall thickness + 2 x 50mm = 500mm)

 

The SE's width will be based on loading and [assumed if no GI available] ground conditions. Going wider is no problem. 

[joe90]

My founds were 700mm on clay, specified by the BCO, digger driver used 600mm bucket but scraped it wider . 450 is just the minimum!

[DannyG]

Thanks all, I'll query this with our SE.

[Conor]

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Edited July 8, 2022 by Conor
Wrong thread

[DannyG]

Not a retaining wall, just the external walls of our house. The 450mm section is single story with the 2-story section having 600mm wide and all are 1500mm deep.

[Canski]

I would just go for the 600 mm trench. 400 wall on a 450mm footing is like you say a bit too tight.

 

[Chanmenie]

My walls are 380mm, I went with 600mm and that’s still a bit tight, so I would go with at least 600mm, 450 with 400 walls would be a nightmare.

I was lucky in that I only needed to go 700mm deep as on sand and gravel.