Extension foundation level

[firapara]

Hi Guys,

Building an extension.

Is it normal to have a new extension foundation 20 cm higher than the original house foundation? See attached drawing.

Or should it be level with the existing house foundation?

Structural engineer specified a minimum 40cm from the foundation to the ground level for the extension, but the existing house foundation is 60cm below the ground level.

Thanks

 

[^woody^]

At least the same as existing, often deeper.

 

[johnny2007]

As long as it doesn't bridge the original dpc.
I take that this is all below ground level, so it'll be ok.

 

[firapara]

Extension foundation is deeper, because if a new tree nearby.

 

[firapara]

As long as it doesn't bridge the original dpc.
I take that this is all below ground level, so it'll be ok.

It will not bridge the original DPC, yes it is all below the ground level

 

[firapara]

At least the same as existing, often deeper.

Extension foundation is deeper, because if a new tree nearby.

 

[noseall]

Is it normal to have a new extension foundation 20 cm higher than the original house foundation?

No. There is no normal.

What folk are telling you is that the trench bottom is important, then the thickness of the (mass filled) concrete will be determined by how many courses of brick you intend building up to DPC - then set your trench pegs at this height. There is no normal. For clarity, our extension foundations, almost always finish a wee bit higher than the existing.