Foundation depth

[CharlesBR]

When the depth of a building's foundation is measured to ensure a first floor extension can be built on is the brick that sits on the footing included or the concrete footing just measured? I always assumed it was just the concrete footing?

The type of soil we have is reasonably thick clay and I am planning on having a first floor timber frame extension added on top of brick structure so just wondering how deep my foundations need to be.

 

[^woody^]

Anything below ground level is the "foundation". Foundation depth is measured from the lowest ground level.

 

[CharlesBR]

Anything below ground level is the "foundation". Foundation depth is measured from the lowest ground level.

Thanks @^woody^ - clarity as always