As you say, there is no definition of what is included in the Fee apart from it's not Defined Cost.
At a high level, it is:
For options A & B:
- profit,
- head office overheads and
- under NEC3, an allowance for the cost of preparing quotations
For options C, D & E:
- profit,
- head office overheads,
- cost of taking out insurances,
- an allowance for Disallowed Costs.
Under F:
- all costs not subcontracted except for items identified for lump sum payments in Contract Data part 2.
At a high level, it is:
For options A & B:
- profit,
- head office overheads and
- under NEC3, an allowance for the cost of preparing quotations
For options C, D & E:
- profit,
- head office overheads,
- cost of taking out insurances,
- an allowance for Disallowed Costs.
Under F:
- all costs not subcontracted except for items identified for lump sum payments in Contract Data part 2.
