We're digging the footings for my daughter's single storey, timber framed extension (3.5m x 7m) and the architect/structural engineer has specified a concrete raft foundation with steel reinforcement and a ring beam around the edge (presumably because strip foundations would need to be over 2 metres deep to get past clay to solid ground). Depth of concrete is specced at 175mm with 225mm hardcore beneath with a greater (unspecified) depth and width at the edges.
This 225mm seems to be a hell of a lot of hardcore and means a load of digging which we could do without (we can't get a mini-digger onto the site so it's all manual hard labour).
Questions:
1) Is the 225mm reasonable and/or necessary ? Can I safely reduce this maybe depending upon ground conditions after consultation with the BCO ?
2) Typically, what is the additional depth/width needed for the edge footings to accommodate the ring beam ?
Thanks
Ron
This 225mm seems to be a hell of a lot of hardcore and means a load of digging which we could do without (we can't get a mini-digger onto the site so it's all manual hard labour).
Questions:
1) Is the 225mm reasonable and/or necessary ? Can I safely reduce this maybe depending upon ground conditions after consultation with the BCO ?
2) Typically, what is the additional depth/width needed for the edge footings to accommodate the ring beam ?
Thanks
Ron